ZOONOMIA;

OR,

THE LAWS

OF

ORGANIC LIFE.

VOL. I.

By ERASMUS DARWIN, M.D. F.R.S.

AUTHOR OF THE BOTANIC GARDEN.

THE SECOND EDITION, CORRECTED.

LONDON:
PRINTED FOR. J. JOHNSON, IN ST. PAUL’S CHURCH-YARD.
1796.

Entered at Stationers’ Hall.

DEDICATION.

To the candid and ingenious Members of the College of Physicians, of
the Royal Philosophical Society, of the Two Universities, and to all
those, who study the Operations of the Mind as a Science, or who practice
Medicine as a Profession, the subsequent Work is, with great respect,
inscribed by the Author,

DERBY, May 1, 1794.

CONTENTS.

TO

ERASMUS DARWIN,

ON HIS WORK INTITLED

ZOONOMIA,

By DEWHURST BILSBORROW.

TRIN. COL. CAMBRIDGE, Jan. 1, 1794.

REFERENCES TO THE WORK.

PREFACE.

The purport of the following pages is an endeavour to reduce the facts
belonging to ANIMAL LIFE
into classes, orders, genera, and species; and, by comparing them with
each other, to unravel the theory of diseases. It happened, perhaps
unfortunately for the inquirers into the knowledge of diseases, that
other sciences had received improvement previous to their own; whence,
instead of comparing the properties belonging to animated nature with
each other, they, idly ingenious, busied themselves in attempting to
explain the laws of life by those of mechanism and chemistry; they
considered the body as an hydraulic machine, and the fluids as passing
through a series of chemical changes, forgetting that animation was its
essential characteristic.

The great CREATOR of all things has infinitely
diversified the works of his hands, but has at the same time stamped a
certain similitude on the features of nature, that demonstrates to us,
that the whole is one family of one parent. On this similitude is
founded all rational analogy; which, so long as it is concerned in
comparing the essential properties of bodies, leads us to many and
important discoveries; but when with licentious activity it links
together objects, otherwise discordant, by some fanciful similitude; it
may indeed collect ornaments for wit and poetry, but philosophy and truth
recoil from its combinations.

The want of a theory, deduced from such strict analogy, to conduct the
practice of medicine is lamented by its professors; for, as a great
number of unconnected facts are difficult to be acquired, and to be
reasoned from, the art of medicine is in many instances less efficacious
under the direction of its wisest practitioners; and by that busy crowd,
who either boldly wade in darkness, or are led into endless error by the
glare of false theory, it is daily practised to the destruction of
thousands; add to this the unceasing injury which accrues to the public
by the perpetual advertisements of pretended nostrums; the minds of the
indolent become superstitiously fearful of diseases, which they do not
labour under; and thus become the daily prey of some crafty empyric.

A theory founded upon nature, that should bind together the scattered
facts of medical knowledge, and converge into one point of view the laws
of organic life, would thus on many accounts contribute to the interest
of society. It would capacitate men of moderate abilities to practise the
art of healing with real advantage to the public; it would enable every
one of literary acquirements to distinguish the genuine disciples of
medicine from those of boastful effrontery, or of wily address; and would
teach mankind in some important situations the knowledge of
themselves.

There are some modern practitioners, who declaim against medical
theory in general, not considering that to think is to theorize; and that
no one can direct a method of cure to a person labouring under disease
without thinking, that is, without theorizing; and happy therefore is the
patient, whose physician possesses the best theory.

The words idea, perception, sensation, recollection, suggestion, and
association, are each of them used in this treatise in a more limited
sense than in the writers of metaphysic. The author was in doubt, whether
he should rather have substituted new words instead of them; but was at
length of opinion, that new definitions of words already in use would be
less burthensome to the memory of the reader.

A great part of this work has lain by the writer above twenty years,
as some of his friends can testify: he had hoped by frequent revision to
have made it more worthy the acceptance of the public; this however his
other perpetual occupations have in part prevented, and may continue to
prevent, as long as he may be capable of revising it; he therefore begs
of the candid reader to accept of it in its present state, and to excuse
any inaccuracies of expression, or of conclusion, into which the
intricacy of his subject, the general imperfection of language, or the
frailty he has in common with other men, may have betrayed him; and from
which he has not the vanity to believe this treatise to be exempt.

ZOONOMIA.

SECT. I.

OF MOTION.

The whole of nature may be supposed to consist of two essences or
substances; one of which may be termed spirit, and the other matter. The
former of these possesses the power to commence or produce motion, and
the latter to receive and communicate it. So that motion, considered as a
cause, immediately precedes every effect; and, considered as an effect,
it immediately succeeds every cause.

The MOTIONS OF MATTER may be divided into two
kinds, primary and secondary. The secondary motions are those, which are
given to or received from other matter in motion. Their laws have been
successfully investigated by philosophers in their treatises on mechanic
powers. These motions are distinguished by this circumstance, that the
velocity multiplied into the quantity of matter of the body acted upon is
equal to the velocity multiplied into the quantity of matter of the
acting body.

The primary motions of matter may be divided into three classes, those
belonging to gravitation, to chemistry, and to life; and each class has
its peculiar laws. Though these three classes include the motions of
solid, liquid, and aerial bodies; there is nevertheless a fourth division
of motions; I mean those of the supposed ethereal fluids of magnetism,
electricity, heat, and light; whose properties are not so well
investigated as to be classed with sufficient accuracy.

1st. The gravitating motions include the annual and diurnal
rotation of the earth and planets, the flux and reflux of the ocean, the
descent of heavy bodies, and other phænomena of gravitation. The
unparalleled sagacity of the great NEWTON has
deduced the laws of this class of motions from the simple principle of
the general attraction of matter. These motions are distinguished by
their tendency to or from the centers of the sun or planets.

2d. The chemical class of motions includes all the various
appearances of chemistry. Many of the facts, which belong to these
branches of science, are nicely ascertained, and elegantly classed; but
their laws have not yet been developed from such simple principles as
those above-mentioned; though it is probable, that they depend on the
specific attractions belonging to the particles of bodies, or to the
difference of the quantity of attraction belonging to the sides and
angles of those particles. The chemical motions are distinguished by
their being generally attended with an evident decomposition or new
combination of the active materials.

3d. The third class includes all the motions of the animal and
vegetable world; as well those of the vessels, which circulate their
juices, and of the muscles, which perform their locomotion, as those of
the organs of sense, which constitute their ideas.

This last class of motion is the subject of the following pages;
which, though conscious of their many imperfections, I hope may give some
pleasure to the patient reader, and contribute something to the knowledge
and to the cure of diseases.

SECT. II.

EXPLANATIONS AND DEFINITIONS.

I. Outline of the animal
economy.—II. 1. Of the sensorium. 2. Of the brain and nervous medulla. 3. A nerve. 4.
A muscular fibre. 5. The immediate
organs of sense. 6. The external organs
of sense. 7. An idea or sensual
motion. 8. Perception. 9. Sensation. 10. Recollection and suggestion. 11. Habit, causation, association,
catenation. 12. Reflex ideas. 13. Stimulus defined.

As some explanations and definitions will be necessary in the
prosecution of the work, the reader is troubled with them in this place,
and is intreated to keep them in his mind as he proceeds, and to take
them for granted, till an apt opportunity occurs to evince their truth;
to which I shall premise a very short outline of the animal economy.

I.—1. The
nervous system has its origin from the brain, and is distributed to every
part of the body. Those nerves, which serve the senses, principally arise
from that part of the brain, which is lodged in the head; and those,
which serve the purposes of muscular motion, principally arise from that
part of the brain, which is lodged in the neck and back, and which is
erroneously called the spinal marrow. The ultimate fibrils of these
nerves terminate in the immediate organs of sense and muscular fibres,
and if a ligature be put on any part of their passage from the head or
spine, all motion and perception cease in the parts beneath the
ligature.

2. The longitudinal muscular fibres compose
the locomotive muscles, whose contractions move the bones of the limbs
and trunk, to which their extremities are attached. The annular or spiral
muscular fibres compose the vascular muscles, which constitute the
intestinal canal, the arteries, veins, glands, and absorbent vessels.

3. The immediate organs of sense, as the
retina of the eye, probably consist of moving fibrils, with a power of
contraction similar to that of the larger muscles above described.

4. The cellular membrane consists of cells,
which resemble those of a sponge, communicating with each other, and
connecting together all the other parts of the body.

5. The arterial system consists of the
aortal and the pulmonary artery, which are attended through their whole
course with their correspondent veins. The pulmonary artery receives the
blood from the right chamber of the heart, and carries it to the minute
extensive ramifications of the lungs, where it is exposed to the action
of the air on a surface equal to that of the whole external skin, through
the thin moist coats of those vessels, which are spread on the air-cells,
which constitute the minute terminal ramifications of the wind-pipe. Here
the blood changes its colour from a dark red to a bright scarlet. It is
then collected by the branches of the pulmonary vein, and conveyed to the
left chamber of the heart.

6. The aorta is another large artery, which
receives the blood from the left chamber of the heart, after it has been
thus aerated in the lungs, and conveys it by ascending and descending
branches to every other part of the system; the extremities of this
artery terminate either in glands, as the salivary glands, lacrymal
glands, &c. or in capillary vessels, which are probably less
involuted glands; in these some fluid, as saliva, tears, perspiration,
are separated from the blood; and the remainder of the blood is absorbed
or drank up by branches of veins correspondent to the branches of the
artery; which are furnished with valves to prevent its return; and is
thus carried back, after having again changed its colour to a dark red,
to the right chamber of the heart. The circulation of the blood in the
liver differs from this general system; for the veins which drink up the
refluent blood from those arteries, which are spread on the bowels and
mesentery, unite into a trunk in the liver, and form a kind of artery,
which is branched into the whole substance of the liver, and is called
the vena portarum; and from which the bile is separated by the numerous
hepatic glands, which constitute that viscus.

7. The glands may be divided into three
systems, the convoluted glands, such as those above described, which
separate bile, tears, saliva, &c. Secondly, the glands without
convolution, as the capillary vessels, which unite the terminations of
the arteries and veins; and separate both the mucus, which lubricates the
cellular membrane, and the perspirable matter, which preserves the skin
moist and flexible. And thirdly, the whole absorbent system, consisting
of the lacteals, which open their mouths into the stomach and intestines,
and of the lymphatics, which open their mouths on the external surface of
the body, and on the internal linings of all the cells of the cellular
membrane, and other cavities of the body.

These lacteal and lymphatic vessels are furnished with numerous valves
to prevent the return of the fluids, which they absorb, and terminate in
glands, called lymphatic glands, and may hence be considered as long
necks or mouths belonging to these glands. To these they convey the chyle
and mucus, with a part of the perspirable matter, and atmospheric
moisture; all which, after having passed through these glands, and having
suffered some change in them, are carried forward into the blood, and
supply perpetual nourishment to the system, or replace its hourly
waste.

8. The stomach and intestinal canal have a
constant vermicular motion, which carries forwards their contents, after
the lacteals have drank up the chyle from them; and which is excited into
action by the stimulus of the aliment we swallow, but which becomes
occasionally inverted or retrograde, as in vomiting, and in the iliac
passion.

II. 1. The word
sensorium in the following pages is designed to express not only
the medullary part of the brain, spinal marrow, nerves, organs of sense,
and of the muscles; but also at the same time that living principle, or
spirit of animation, which resides throughout the body, without being
cognizable to our senses, except by its effects. The changes which
occasionally take place in the sensorium, as during the exertions of
volition, or the sensations of pleasure or pain, are termed sensorial
motions.

2. The similarity of the texture of the
brain to that of the pancreas, and some other glands of the body, has
induced the inquirers into this subject to believe, that a fluid, perhaps
much more subtile than the electric aura, is separated from the blood by
that organ for the purposes of motion and sensation. When we recollect,
that the electric fluid itself is actually accumulated and given out
voluntarily by the torpedo and the gymnotus electricus, that an electric
shock will frequently stimulate into motion a paralytic limb, and lastly
that it needs no perceptible tubes to convey it, this opinion seems not
without probability; and the singular figure of the brain and nervous
system seems well adapted to distribute it over every part of the
body.

For the medullary substance of the brain not only occupies the
cavities of the head and spine, but passes along the innumerable
ramifications of the nerves to the various muscles and organs of sense.
In these it lays aside its coverings, and is intermixed with the slender
fibres, which constitute those muscles and organs of sense. Thus all
these distant ramifications of the sensorium are united at one of their
extremities, that is, in the head and spine; and thus these central parts
of the sensorium constitute a communication between all the organs of
sense and muscles.

3. A nerve is a continuation of the
medullary substance of the brain from the head or spine towards the other
parts of the body, wrapped in its proper membrane.

4. The muscular fibres are moving
organs intermixed with that medullary substance, which is continued along
the nerves, as mentioned above. They are indued with the power of
contraction, and are again elongated either by antagonist muscles, by
circulating fluids, or by elastic ligaments. So the muscles on one side
of the forearm bend the fingers by means of their tendons, and those on
the other side of the fore-arm extend them again. The arteries are
distended by the circulating blood; and in the necks of quadrupeds there
is a strong elastic ligament, which assists the muscles, which elevate
the head, to keep it in its horizontal position, and to raise it after it
has been depressed.

5. The immediate organs of sense
consist in like manner of moving fibres enveloped in the medullary
substance above mentioned; and are erroneously supposed to be simply an
expansion of the nervous medulla, as the retina of the eye, and the rete
mucosum of the skin, which are the immediate organs of vision, and of
touch. Hence when we speak of the contractions of the fibrous parts of
the body, we shall mean both the contractions of the muscles, and those
of the immediate organs of sense. These fibrous motions are thus
distinguished from the sensorial motions above mentioned.

6. The external organs of sense are
the coverings of the immediate organs of sense, and are mechanically
adapted for the reception or transmission of peculiar bodies, or of their
qualities, as the cornea and humours of the eye, the tympanum of the ear,
the cuticle of the fingers and tongue.

7. The word idea has various meanings
in the writers of metaphysic: it is here used simply for those notions of
external things, which our organs of sense bring us acquainted with
originally; and is defined a contraction, or motion, or configuration, of
the fibres, which constitute the immediate organ of sense; which will be
explained at large in another part of the work. Synonymous with the word
idea, we shall sometimes use the words sensual motion in
contradistinction to muscular motion.

8. The word perception includes both
the action of the organ of sense in consequence of the impact of external
objects, and our attention to that action; that is, it expresses both the
motion of the organ of sense, or idea, and the pain or pleasure that
succeeds or accompanies it.

9. The pleasure or pain which necessarily
accompanies all those perceptions or ideas which we attend to, either
gradually subsides, or is succeeded by other fibrous motions. In the
latter case it is termed sensation, as explained in Sect. V. 2, and VI. 2.—The
reader is intreated to keep this in his mind, that through all this
treatise the word sensation is used to express pleasure or pain only in
its active state, by whatever means it is introduced into the system,
without any reference to the stimulation of external objects.

10. The vulgar use of the word
memory is too unlimited for our purpose: those ideas which we
voluntarily recall are here termed ideas of recollection, as when
we will to repeat the alphabet backwards. And those ideas which are
suggested to us by preceding ideas are here termed ideas of
suggestion, as whilst we repeat the alphabet in the usual order;
when by habits previously acquired B is suggested by A, and C by B,
without any effort of deliberation.

11. The word association properly
signifies a society or convention of things in some respects similar to
each other. We never say in common language, that the effect is
associated with the cause, though they necessarily accompany or succeed
each other. Thus the contractions of our muscles and organs of sense may
be said to be associated together, but cannot with propriety be said to
be associated with irritations, or with volition, or with sensation;
because they are caused by them, as mentioned in Sect. IV. When fibrous contractions succeed other fibrous
contractions, the connection is termed association; when fibrous
contractions succeed sensorial motions, the connection is termed
causation; when fibrous and sensorial motions reciprocally
introduce each other in progressive trains or tribes, it is termed
catenation of animal motions. All these connections are said to be
produced by habit; that is, by frequent repetition.

12. It may be proper to observe, that by
the unavoidable idiom of our language the ideas of perception, of
recollection, or of imagination, in the plural number signify the ideas
belonging to perception, to recollection, or to imagination; whilst the
idea of perception, of recollection, or of imagination, in the singular
number is used for what is termed “a reflex idea of any of those
operations of the sensorium.”

13. By the word stimulus is not only
meant the application of external bodies to our organs of sense and
muscular fibres, which excites into action the sensorial power termed
irritation; but also pleasure or pain, when they excite into action the
sensorial power termed sensation; and desire or aversion, when they
excite into action the power of volition; and lastly, the fibrous
contractions which precede association; as is further explained in Sect.
XII. 2. 1.

SECT. III.

THE MOTIONS OF THE RETINA DEMONSTRATED BY EXPERIMENTS.

I. Of animal motions and of ideas. II. The fibrous structure of the retina. III. The activity of the retina in vision.
1. Rays of light have no momentum. 2. Objects long viewed become fainter. 3. Spectra of black objects become
luminous. 4. Varying spectra from
gyration. 5. From long inspection of
various colours. IV. Motions of the
organs of sense constitute ideas. 1.
Light from pressing the eye-ball, and sound from the pulsation of the
carotid artery. 2. Ideas in sleep
mistaken for perceptions. 3. Ideas of
imagination produce pain and sickness like sensations. 4. When the organ of sense is destroyed, the
ideas belonging to that sense perish. V.
Analogy between muscular motions and sensual motions, or ideas. 1. They are both originally excited by
irritations. 2. And associated
together in the same manner. 3. Both
act in nearly the same times. 4. Are
alike strengthened or fatigued by exercise. 5. Are alike painful from inflammation.
6. Are alike benumbed by compression.
7. Are alike liable to paralysis. 8. To convulsion. 9. To the influence of old age.—VI. Objections answered. 1. Why we cannot invent new ideas. 2. If ideas resemble external objects. 3. Of the imagined sensation in an amputated
limb. 4. Abstract ideas.—VII. What are ideas, if they are not animal
motions?

Before the great variety of animal motions can be duly arranged into
natural classes and orders, it is necessary to smooth the way to this yet
unconquered field of science, by removing some obstacles which thwart our
passage. I. To demonstrate that the retina and
other immediate organs of sense possess a power of motion, and that these
motions constitute our ideas, according to the fifth and seventh of the
preceding assertions, claims our first attention.

Animal motions are distinguished from the communicated motions,
mentioned in the first section, as they have no mechanical proportion to
their cause; for the goad of a spur on the skin of a horse shall induce
him to move a load of hay. They differ from the gravitating motions there
mentioned as they are exerted with equal facility in all directions, and
they differ from the chemical class of motions, because no apparent
decompositions or new combinations are produced in the moving
materials.

Hence, when we say animal motion is excited by irritation, we do not
mean that the motion bears any proportion to the mechanical impulse of
the stimulus; nor that it is affected by the general gravitation of the
two bodies; nor by their chemical properties, but solely that certain
animal fibres are excited into action by something external to the moving
organ.

In this sense the stimulus of the blood produces the contractions of
the heart; and the substances we take into our stomach and bowels
stimulate them to perform their necessary functions. The rays of light
excite the retina into animal motion by their stimulus; at the same time
that those rays of light themselves are physically converged to a focus
by the inactive humours of the eye. The vibrations of the air stimulate
the auditory nerve into animal action; while it is probable that the
tympanum of the ear at the same time undergoes a mechanical
vibration.

To render this circumstance more easy to be comprehended, motion
may be defined to be a variation of figure; for the whole universe
may be considered as one thing possessing a certain figure; the motions
of any of its parts are a variation of this figure of the whole: this
definition of motion will be further explained in Section XIV. 2. 2. on the production of ideas.

Now the motions of an organ of sense are a succession of
configurations of that organ; these configurations succeed each other
quicker or slower; and whatever configuration of this organ of sense,
that is, whatever portion of the motion of it is, or has usually been,
attended to, constitutes an idea. Hence the configuration is not to be
considered as an effect of the motion of the organ, but rather as a part
or temporary termination of it; and that, whether a pause succeeds it, or
a new configuration immediately takes place. Thus when a succession of
moving objects are presented to our view, the ideas of trumpets, horns,
lords and ladies, trains and canopies, are configurations, that is, parts
or links of the successive motions of the organ of vision.

Plate I.

These motions or configurations of the organs of sense differ from the
sensorial motions to be described hereafter, as they appear to be simply
contractions of the fibrous extremities of those organs, and in that
respect exactly resemble the motions or contractions of the larger
muscles, as appears from the following experiment. Place a circular piece
of red silk about an inch in diameter on a sheet of white paper in a
strong light, as in Plate I.—look for a minute on this area, or
till the eye becomes somewhat fatigued, and then, gently closing your
eyes, and shading them with your hand, a circular green area of the same
apparent diameter becomes visible in the closed eye. This green area is
the colour reverse to the red area, which had been previously inspected,
as explained in the experiments on ocular spectra at the end of the work,
and in Botanical Garden, P. 1. additional note, No. 1. Hence it appears,
that a part of the retina, which had been fatigued by contraction in one
direction, relieves itself by exerting the antagonist fibres, and
producing a contraction in an opposite direction, as is common in the
exertions of our muscles. Thus when we are tired with long action of our
arms in one direction, as in holding a bridle on a journey, we
occasionally throw them into an opposite position to relieve the fatigued
muscles.

Mr. Locke has defined an idea to be “whatever is present to the mind;”
but this would include the exertions of volition, and the sensations of
pleasure and pain, as well as those operations of our system, which
acquaint us with external objects; and is therefore too unlimited for our
purpose. Mr. Lock seems to have fallen into a further error, by
conceiving, that the mind could form a general or abstract idea by its
own operation, which was the copy of no particular perception; as of a
triangle in general, that was neither acute, obtuse, nor right angled.
The ingenious Dr. Berkley and Mr. Hume have demonstrated, that such
general ideas have no existence in nature, not even in the mind of their
celebrated inventor. We shall therefore take for granted at present, that
our recollection or imagination of external objects consists of a partial
repetition of the perceptions, which were excited by those external
objects, at the time we became acquainted with them; and that our reflex
ideas of the operations of our minds are partial repetitions of those
operations.

II. The following article evinces that the
organ of vision consists of a fibrous part as well as of the nervous
medulla, like other white muscles; and hence, as it resembles the
muscular parts of the body in its structure, we may conclude, that it
must resemble them in possessing a power of being excited into animal
motion.—The subsequent experiments on the optic nerve, and on the
colours remaining in the eye, are copied from a paper on ocular spectra
published in the seventy-sixth volume of the Philos. Trans. by Dr. R.
Darwin of Shrewsbury; which, as I shall have frequent occasion to refer
to, is reprinted in this work, Sect. XL. The
retina of an ox’s eye was suspended in a glass of warm water, and
forcibly torn in a few places; the edges of these parts appeared jagged
and hairy, and did not contract and become smooth like simple mucus, when
it is distended till it breaks; which evinced that it consisted of
fibres. This fibrous construction became still more distinct to the light
by adding some caustic alcali to the water; as the adhering mucus was
first eroded, and the hair-like fibres remained floating in the vessel.
Nor does the degree of transparency of the retina invalidate this
evidence of its fibrous structure, since Leeuwenhoek has shewn, that the
crystalline humour itself consists of fibres. Arc. Nat. V. I. 70.

Hence it appears, that as the muscles consist of larger fibres
intermixed with a smaller quantity of nervous medulla, the organ of
vision consists of a greater quantity of nervous medulla intermixed with
smaller fibres. It is probable that the locomotive muscles of microscopic
animals may have greater tenuity than these of the retina; and there is
reason to conclude from analogy, that the other immediate organs of
sense, as the portio mollis of the auditory nerve, and the rete mucosum
of the skin, possess a similarity of structure with the retina, and a
similar power of being excited into animal motion.

III. The subsequent articles shew, that
neither mechanical impressions, nor chemical combinations of light, but
that the animal activity of the retina constitutes vision.

1. Much has been conjectured by
philosophers about the momentum of the rays of light; to subject this to
experiment a very light horizontal balance was constructed by Mr. Michel,
with about an inch square of thin leaf-copper suspended at each end of
it, as described in Dr. Priestley’s History of Light and Colours. The
focus of a very large convex mirror was thrown by Dr. Powel, in his
lectures on experimental philosophy, in my presence, on one wing of this
delicate balance, and it receded from the light; thrown on the other
wing, it approached towards the light, and this repeatedly; so that no
sensible impulse could be observed, but what might well be ascribed to
the ascent of heated air.

Whence it is reasonable to conclude, that the light of the day must be
much too weak in its dilute state to make any mechanical impression on so
tenacious a substance as the retina of the eye.—Add to this, that
as the retina is nearly transparent, it could therefore make less
resistance to the mechanical impulse of light; which, according, to the
observations related by Mr. Melvil in the Edinburgh Literary Essays, only
communicates heat, and should therefore only communicate momentum, where
it is obstructed, reflected, or refracted.—From whence also may be
collected the final cause of this degree of transparency of the retina,
viz. left by the focus of stronger lights, heat and pain should have been
produced in the retina, instead of that stimulus which excites it into
animal motion.

2. On looking long on an area of scarlet
silk of about an inch in diameter laid on white paper, as in Plate I. the
scarlet colour becomes fainter, till at length it entirely vanishes,
though the eye is kept uniformly and steadily upon it. Now if the change
or motion of the retina was a mechanical impression, or a chemical tinge
of coloured light, the perception would every minute become stronger and
stronger,—whereas in this experiment it becomes every instant
weaker and weaker. The same circumstance obtains in the continued
application of sound, or of sapid bodies, or of odorous ones, or of
tangible ones, to their adapted organs of sense.

Plate II.

Thus when a circular coin, as a shilling, is pressed on the palm of
the hand, the sense of touch is mechanically compressed; but it is the
stimulus of this pressure that excites the organ of touch into animal
action, which constitutes the perception of hardness and of figure; for
in some minutes the perception ceases, though the mechanical pressure of
the object remains.

3. Make with ink on white paper a very
black spot about half an inch in diameter, with a tail about an inch in
length, so as to resemble a tadpole, as in Plate II.; look steadfastly
for a minute on the center of this spot, and, on moving the eye a little,
the figure of the tadpole will be seen on the white part of the paper;
which figure of the tadpole will appear more luminous than the other part
of the white paper; which can only be explained by supposing that a part
of the retina, on which the tadpole was delineated, to have become more
sensible to light than the other parts of it, which were exposed to the
white paper; and not from any idea of mechanical impression or chemical
combination of light with the retina.

4. When any one turns round rapidly, till
he becomes dizzy, and falls upon the ground, the spectra of the ambient
objects continue to present themselves in rotation, and he seems to
behold the objects still in motion. Now if these spectra were impressions
on a passive organ, they either must continue as they were received last,
or not continue at all.

5. Place a piece of red silk about an inch
in diameter on a sheet of white paper in a strong light, as in Plate I;
look steadily upon it from the distance of about half a yard for a
minute; then closing your eye-lids, cover them with your hands and
handkerchief, and a green spectrum will be seen in your eyes resembling
in form the piece of red silk. After some seconds of time the spectrum
will disappear, and in a few more seconds will reappear; and thus
alternately three or four times, if the experiment be well made, till at
length it vanishes entirely.

Plate III.

6. Place a circular piece of white paper,
about four inches in diameter, in the sunshine, cover the center of this
with a circular piece of black silk, about three inches in diameter; and
the center of the black silk with a circle of pink silk, about two inches
in diameter; and the center of the pink silk with a circle of yellow
silk, about one inch in diameter; and the center of this with a circle of
blue silk, about half an inch in diameter; make a small spot with ink in
the center of the blue silk, as in Plate III.; look steadily for a minute
on this central spot, and then closing your eyes, and applying your hand
at about an inch distance before them, so as to prevent too much or too
little light from passing through the eye-lids, and you will see the most
beautiful circles of colours that imagination can conceive; which are
most resembled by the colours occasioned by pouring a drop or two of oil
on a still lake in a bright day. But these circular irises of colours are
not only different from the colours of the silks above mentioned, but are
at the same time perpetually changing as long as they exist.

From all these experiments it appears, that these spectra in the eye
are not owing to the mechanical impulse of light impressed on the retina;
nor to its chemical combination with that organ; nor to the absorption
and emission of light, as is supposed, perhaps erroneously, to take place
in calcined shells and other phosphorescent bodies, after having been
exposed to the light: for in all these cases the spectra in the eye
should either remain of the same colour, or gradually decay, when the
object is withdrawn; and neither their evanescence during the presence of
their object, as in the second experiment, nor their change from dark to
luminous, as in the third experiment, nor their rotation, as in the
fourth experiment, nor the alternate presence and evanescence of them, as
in the fifth experiment, nor the perpetual change of colours of them, as
in the last experiment, could exist.

IV. The subsequent articles shew, that these
animal motions or configurations of our organs of sense constitute our
ideas.

1. If any one in the dark presses the ball
of his eye, by applying his finger to the external corner of it, a
luminous appearance is observed; and by a smart stroke on the eye great
slashes of fire are perceived. (Newton’s Optics.) So that when the
arteries, that are near the auditory nerve, make stronger pulsations than
usual, as in some fevers, an undulating sound is excited in the ears.
Hence it is not the presence of the light and sound, but the motions of
the organ, that are immediately necessary to constitute the perception or
idea of light and sound.

2. During the time of sleep, or in
delirium, the ideas of imagination are mistaken for the perceptions of
external objects; whence it appears, that these ideas of imagination, are
no other than a reiteration of those motions of the organs of sense,
which were originally excited by the stimulus of external objects: and in
our waking hours the simple ideas, that we call up by recollection or by
imagination, as the colour of red, or the smell of a rose, are exact
resemblances of the same simple ideas from perception; and in consequence
must be a repetition of those very motions.

3. The disagreeable sensation called the
tooth-edge is originally excited by the painful jarring of the teeth in
biting the edge of the glass, or porcelain cup, in which our food was
given us in our infancy, as is further explained in the Section XVI. 10, on Instinct.—This disagreeable
sensation is afterwards excitable not only by a repetition of the sound,
that was then produced, but by imagination alone, as I have myself
frequently experienced; in this case the idea of biting a china cup, when
I imagine it very distinctly, or when I see another person bite a cup or
glass, excites an actual pain in the nerves of my teeth. So that this
idea and pain seem to be nothing more than the reiterated motions of
those nerves, that were formerly so disagreeably affected.

Other ideas that are excited by imagination or recollection in many
instances produce similar effects on the constitution, as our perceptions
had formerly produced, and are therefore undoubtedly a repetition of the
same motions. A story which the celebrated Baron Van Swieton relates of
himself is to this purpose. He was present when the putrid carcase of a
dead dog exploded with prodigious stench; and some years afterwards,
accidentally riding along the same road, he was thrown into the same
sickness and vomiting by the idea of the stench, as he had before
experienced from the perception of it.

4. Where the organ of sense is totally
destroyed, the ideas which were received by that organ seem to perish
along with it, as well as the power of perception. Of this a satisfactory
instance has fallen under my observation. A gentleman about sixty years
of age had been totally deaf for near thirty years: he appeared to be a
man of good understanding, and amused himself with reading, and by
conversing either by the use of the pen, or by signs made with his
fingers, to represent letters. I observed that he had so far forgot the
pronunciation of the language, that when he attempted to speak, none of
his words had distinct articulation, though his relations could sometimes
understand his meaning. But, which is much to the point, he assured me,
that in his dreams he always imagined that people conversed with him by
signs or writing, and never that he heard any one speak to him. From
hence it appears, that with the perceptions of sounds he has also lost
the ideas of them; though the organs of speech still retain somewhat of
their usual habits of articulation.

This observation may throw some light on the medical treatment of deaf
people; as it may be learnt from their dreams whether the auditory nerve
be paralytic, or their deafness be owing to some defect of the external
organ.

It rarely happens that the immediate organ of vision is perfectly
destroyed. The most frequent causes of blindness are occasioned by
defects of the external organ, as in cataracts and obfuscations of the
cornea. But I have had the opportunity of conversing with two men, who
had been some years blind; one of them had a complete gutta serena, and
the other had lost the whole substance of his eyes. They both told me
that they did not remember to have ever dreamt of visible objects, since
the total loss of their sight.

V. Another method of discovering that our
ideas are animal motions of the organs of sense, is from considering the
great analogy they bear to the motions of the larger muscles of the body.
In the following articles it will appear that they are originally excited
into action by the irritation of external objects like our muscles; are
associated together like our muscular motions; act in similar time with
them; are fatigued by continued exertion like them; and that the organs
of sense are subject to inflammation, numbness, palsy, convulsion, and
the defects of old age, in the same manner as the muscular fibres.

1. All our perceptions or ideas of external
objects are universally allowed to have been originally excited by the
stimulus of those external objects; and it will be shewn in a succeeding
section, that it is probable that all our muscular motions, as well those
that are become voluntary as those of the heart and glandular system,
were originally in like manner excited by the stimulus of something
external to the organ of motion.

2. Our ideas are also associated together
after their production precisely in the same manner as our muscular
motions; which will likewise be fully explained in the succeeding
section.

3. The time taken up in performing an idea
is likewise much the same as that taken up in performing a muscular
motion. A musician can press the keys of an harpsichord with his fingers
in the order of a tune he has been accustomed to play, in as little time
as he can run over those notes in his mind. So we many times in an hour
cover our eye-balls with our eye-lids without perceiving that we are in
the dark; hence the perception or idea of light is not changed for that
of darkness in so small a time as the twinkling of an eye; so that in
this case the muscular motion of the eye-lid is performed quicker than
the perception of light can be changed for that of darkness.—So if
a fire-stick be whirled round in the dark, a luminous circle appears to
the observer; if it be whirled somewhat slower, this circle becomes
interrupted in one part; and then the time taken up in such a revolution
of the stick is the same that the observer uses in changing his ideas:
thus the δολικοσκοτον
εγκος of Homer, the long shadow of
the flying javelin, is elegantly designed to give us an idea of its
velocity, and not of its length.

4. The fatigue that follows a continued
attention of the mind to one object is relieved by changing the subject
of our thoughts; as the continued movement of one limb is relieved by
moving another in its stead. Whereas a due exercise of the faculties of
the mind strengthens and improves those faculties, whether of imagination
or recollection; as the exercise of our limbs in dancing or fencing
increases the strength and agility of the muscles thus employed.

5. If the muscles of any limb are inflamed,
they do not move without pain; so when the retina is inflamed, its
motions also are painful. Hence light is as intolerable in this kind of
ophthalmia, as pressure is to the finger in the paronychia. In this
disease the patients frequently dream of having their eyes painfully
dazzled; hence the idea of strong light is painful as well as the
reality. The first of these facts evinces that our perceptions are
motions of the organs of sense; and the latter, that our imaginations are
also motions of the same organs.

6. The organs of sense, like the moving
muscles, are liable to become benumbed, or less sensible, from
compression. Thus, if any person on a light day looks on a white wall, he
may perceive the ramifications of the optic artery, at every pulsation of
it, represented by darker branches on the white wall; which is evidently
owing to its compressing the retina during the diastole of the artery.
Savage Nosolog.

7. The organs of sense and the moving
muscles are alike liable to be affected with palsy, as in the gutta
serena, and in some cases of deafness; and one side of the face has
sometimes lost its power of sensation, but retained its power of motion;
other parts of the body have lost their motions but retained their
sensation, as in the common hemiplagia; and in other instances both these
powers have perished together.

8. In some convulsive diseases a delirium
or insanity supervenes, and the convulsions cease; and conversely the
convulsions shall supervene, and the delirium cease. Of this I have been
a witness many times in a day in the paroxysms of violent epilepsies;
which evinces that one kind of delirium is a convulsion of the organs of
sense, and that our ideas are the motions of these organs: the subsequent
cases will illustrate this observation.

Miss G——, a fair young lady, with light eyes and hair, was
seized with most violent convulsions of her limbs, with outrageous
hiccough, and most vehement efforts to vomit: after near an hour was
elapsed this tragedy ceased, and a calm talkative delirium supervened for
about another hour; and these relieved each other at intervals during the
greatest part of three or four days. After having carefully considered
this disease, I thought the convulsions of her ideas less dangerous than
those of her muscles; and having in vain attempted to make any opiate
continue in her stomach, an ounce of laudanum was rubbed along the spine
of her back, and a dram of it was used as an enema; by this medicine a
kind of drunken delirium was continued many hours; and when it ceased the
convulsions did not return; and the lady continued well many years,
except some lighter relapses, which were relieved in the same manner.

Miss H——, an accomplished young lady, with light eyes and
hair, was seized with convulsions of her limbs, with hiccough, and
efforts to vomit, more violent than words can express; these continued
near an hour, and were succeeded with a cataleptic spasm of one arm, with
the hand applied to her head; and after about twenty minutes these spasms
ceased, and a talkative reverie supervened for near an other hour, from
which no violence, which it was proper to use, could awaken her. These
periods of convulsions, first of the muscles, and then of the ideas,
returned twice a day for several weeks; and were at length removed by
great doses of opium, after a great variety of other medicines and
applications had been in vain experienced. This lady was subject to
frequent relapses, once or twice a year for many years, and was as
frequently relieved by the same method.

Miss W——, an elegant young lady, with black eyes and hair,
had sometimes a violent pain of her side, at other times a most painful
strangury, which were every day succeeded by delirium; which gave a
temporary relief to the painful spasms. After the vain exhibition of
variety of medicines and applications by different physicians, for more
than a twelvemonth, she was directed to take some doses of opium, which
were gradually increased, by which a drunken delirium was kept up for a
day or two, and the pains prevented from returning. A flesh diet, with a
little wine or beer, instead of the low regimen she had previously used,
in a few weeks completely established her health; which, except a few
relapses, has continued for many years.

9. Lastly, as we advance in life all the
parts of the body become more rigid, and are rendered less susceptible of
new habits of motion, though they retain those that were before
established. This is sensibly observed by those who apply themselves late
in life to music, fencing, or any of the mechanic arts. In the same
manner many elderly people retain the ideas they had learned early in
life, but find great difficulty in acquiring new trains of memory;
insomuch that in extreme old age we frequently see a forgetfulness of the
business of yesterday, and at the same time a circumstantial remembrance
of the amusements of their youth; till at length the ideas of
recollection and activity of the body gradually cease
together,—such is the condition of humanity!—and nothing
remains but the vital motions and sensations.

VI. 1. In
opposition to this doctrine of the production of our ideas, it may be
asked, if some of our ideas, like other animal motions, are voluntary,
why can we not invent new ones, that have not been received by
perception? The answer will be better understood after having perused the
succeeding section, where it will be explained, that the muscular motions
likewise are originally excited by the stimulus of bodies external to the
moving organ; and that the will has only the power of repeating the
motions thus excited.

2. Another objector may ask, Can the motion
of an organ of sense resemble an odour or a colour? To which I can only
answer, that it has not been demonstrated that any of our ideas resemble
the objects that excite them; it has generally been believed that they do
not; but this shall be discussed at large in Sect. XIV.

3. There is another objection that at first
view would seem less easy to surmount. After the amputation, of a foot or
a finger, it has frequently happened, that an injury being offered to the
stump of the amputated limb, whether from cold air, too great pressure,
or other accidents, the patient has complained, of a sensation of pain in
the foot or finger, that was cut off. Does not this evince that all our
ideas are excited in the brain, and not in the organs of sense? This
objection is answered, by observing that our ideas of the shape, place,
and solidity of our limbs, are acquired by our organs of touch and of
sight, which are situated in our fingers and eyes, and not by any
sensations in the limb itself.

In this case the pain or sensation, which formerly has arisen in the
foot or toes, and been propagated along the nerves to the central part of
the sensorium, was at the same time accompanied with a visible idea of
the shape and place, and with a tangible idea of the solidity of the
affected limb: now when these nerves are afterwards affected by any
injury done to the remaining stump with a similar degree or kind of pain,
the ideas of the shape, place, or solidity of the lost limb, return by
association; as these ideas belong to the organs of sight and touch, on
which they were first excited.

4. If you wonder what organs of sense can
be excited into motion, when you call up the ideas of wisdom or
benevolence, which Mr. Locke has termed abstracted ideas; I ask you by
what organs of sense you first became acquainted with these ideas? And
the answer will be reciprocal; for it is certain that all our ideas were
originally acquired by our organs of sense; for whatever excites our
perception must be external to the organ that perceives it, and we have
no other inlets to knowledge but by our perceptions: as will be further
explained in Section XIV. and XV. on the Productions and Classes of Ideas.

VII. If our recollection or imagination be
not a repetition of animal movements, I ask, in my turn, What is it? You
tell me it consists of images or pictures of things. Where is this
extensive canvas hung up? or where are the numerous receptacles in which
those are deposited? or to what else in the animal system have they any
similitude?

That pleasing picture of objects, represented in miniature on the
retina of the eye, seems to have given rise to this illusive oratory! It
was forgot that this representation belongs rather to the laws of light,
than to those of life; and may with equal elegance be seen in the camera
obscura as in the eye; and that the picture vanishes for ever, when the
object is withdrawn.

SECT. IV.

LAWS OF ANIMAL CAUSATION.

I. The fibres, which constitute the muscles
and organs of sense, possess a power of contraction. The circumstances
attending the exertion of this power of CONTRACTION constitute the laws of animal motion, as
the circumstances attending the exertion of the power of ATTRACTION constitute the laws of motion of inanimate
matter.

II. The spirit of animation is the immediate
cause of the contraction of animal fibres, it resides in the brain and
nerves, and is liable to general or partial diminution or
accumulation.

III. The stimulus of bodies external to the
moving organ is the remote cause of the original contractions of animal
fibres.

IV. A certain quantity of stimulus produces
irritation, which is an exertion of the spirit of animation exciting the
fibres into contraction.

V. A certain quantity of contraction of animal
fibres, if it be perceived at all, produces pleasure; a greater or less
quantity of contraction, if it be perceived at all, produces pain; these
constitute sensation.

VI. A certain quantity of sensation produces
desire or aversion; these constitute volition.

VII. All animal motions which have occurred at
the same time, or in immediate succession, become so connected, that when
one of them is reproduced, the other has a tendency to accompany or
succeed it. When fibrous contractions succeed or accompany other fibrous
contractions, the connection is termed association; when fibrous
contractions succeed sensorial motions, the connexion is termed
causation; when fibrous and sensorial motions reciprocally introduce each
other, it is termed catenation of animal motions. All these connections
are said to be produced by habit, that is, by frequent repetition. These
laws of animal causation will be evinced by numerous facts, which occur
in our daily exertions; and will afterwards be employed to explain the
more recondite phænomena of the production, growth, diseases, and decay
of the animal system.

SECT. V.

OF THE FOUR FACULTIES OR MOTIONS OF THE SENSORIUM.

1. Four sensorial powers. 2. Irritation, sensation, volition, association
defined. 3. Sensorial motions
distinguished from fibrous motions.

1. The spirit of animation has four different
modes of action, or in other words the animal sensorium possesses four
different faculties, which are occasionally exerted, and cause all the
contractions of the fibrous parts of the body. These are the faculty of
causing fibrous contractions in consequence of the irritations excited by
external bodies, in consequence of the sensations of pleasure or pain, in
consequence of volition, and in consequence of the associations of
fibrous contractions with other fibrous contractions, which precede or
accompany them.

These four faculties of the sensorium during their inactive state are
termed irritability, sensibility, voluntarity, and associability; in
their active state they are termed as above, irritation, sensation,
volition, association.

2. IRRITATION is an
exertion or change of some extreme part of the sensorium residing in the
muscles or organs of sense, in consequence of the appulses of external
bodies.

SENSATION is an exertion or change of the
central parts of the sensorium, or of the whole of it, beginning
at some of those extreme parts of it, which reside in the muscles or
organs of sense.

VOLITION is an exertion or change of the
central parts of the sensorium, or of the whole of it, terminating
in some of those extreme parts of it, which reside in the muscles or
organs of sense.

ASSOCIATION is an exertion or change of some
extreme part of the sensorium residing in the muscles or organs of sense,
in consequence of some antecedent or attendant fibrous contractions.

3. These four faculties of the animal sensorium
may at the time of their exertions be termed motions without impropriety
of language; for we cannot pass from a state of insensibility or inaction
to a state of sensibility or of exertion without some change of the
sensorium, and every change includes motion. We shall therefore sometimes
term the above described faculties sensorial motions to
distinguish them from fibrous motions; which latter expression
includes the motions of the muscles and organs of sense.

The active motions of the fibres, whether those of the muscles or
organs of sense, are probably simple contractions; the fibres being again
elongated by antagonist muscles, by circulating fluids, or sometimes by
elastic ligaments, as in the necks of quadrupeds. The sensorial motions,
which constitute the sensations of pleasure or pain, and which constitute
volition, and which cause the fibrous contractions in consequence of
irritation or of association, are not here supposed to be fluctuations or
refluctuations of the spirit of animation; nor are they supposed to be
vibrations or revibrations, nor condensations or equilibrations of it;
but to be changes or motions of it peculiar to life.

SECT. VI.

OF THE FOUR CLASSES OF FIBROUS MOTIONS.

I. Origin of fibrous contractions. II. Distribution of them into four classes,
irritative motions, sensitive motions, voluntary motions, and associate
motions, defined.

I. All the fibrous contractions of animal
bodies originate from the sensorium, and resolve themselves into four
classes, correspondent with the four powers or motions of the sensorium
above described, and from which they have their causation.

1. These fibrous contractions were
originally caused by the irritations excited by objects, which are
external to the moving organ. As the pulsations of the heart are owing to
the irritations excited by the stimulus of the blood; and the ideas of
perception are owing to the irritations excited by external bodies.

2. But as painful or pleasurable sensations
frequently accompanied those irritations, by habit these fibrous
contractions became causeable by the sensations, and the irritations
ceased to be necessary to their production. As the secretion of tears in
grief is caused by the sensation of pain; and the ideas of imagination,
as in dreams or delirium, are excited by the pleasure or pain, with which
they were formerly accompanied.

3. But as the efforts of the will frequently
accompanied these painful or pleasureable sensations, by habit the
fibrous contractions became causable by volition; and both the
irritations and sensations ceased to be necessary to their production. As
the deliberate locomotions of the body, and the ideas of recollection, as
when we will to repeat the alphabet backwards.

4. But as many of these fibrous contractions
frequently accompanied other fibrous contractions, by habit they became
causable by their associations with them; and the irritations,
sensations, and volition, ceased to be necessary to their production. As
the actions of the muscles of the lower limbs in fencing are associated
with those of the arms; and the ideas of suggestion are associated with
other ideas, which precede or accompany them; as in repeating carelessly
the alphabet in its usual order after having began it.

II. We shall give the following names to these
four classes of fibrous motions, and subjoin their definitions.

1. Irritative motions. That exertion or
change of the sensorium, which is caused by the appulses of external
bodies, either simply subsides, or is succeeded by sensation, or it
produces fibrous motions; it is termed irritation, and irritative motions
are those contractions of the muscular fibres, or of the organs of sense,
that are immediately consequent to this exertion or change of the
sensorium.

2. Sensitive motions. That exertion or
change of the sensorium, which constitutes pleasure or pain, either
simply subsides, or is succeeded by volition, or it produces fibrous
motions; it is termed sensation, and the sensitive motions are those
contractions of the muscular fibres, or of the organs of sense, that are
immediately consequent to this exertion or change of the sensorium.

3. Voluntary motions. That exertion or
change of the sensorium, which constitutes desire or aversion, either
simply subsides, or is succeeded by fibrous motions; it is then termed
volition, and voluntary motions are those contractions of the muscular
fibres, or of the organs of sense, that are immediately consequent to
this exertion or change of the sensorium.

4. Associate motions. That exertion or
change of the sensorium, which accompanies fibrous motions, either simply
subsides, or is succeeded by sensation or volition, or it produces other
fibrous motions; it is then termed association, and the associate motions
are those contractions of the muscular fibres, or of the organs of sense,
that are immediately consequent to this exertion or change of the
sensorium.

SECT. VII.

OF IRRITATIVE MOTIONS.

I. 1. Some
muscular motions are excited by perpetual irritations. 2. Others more frequently by sensations.
3. Others by volition. Case of involuntary
stretchings in paralytic limbs. 4.
Some sensual motions are excited by perpetual irritations. 5. Others more frequently by sensation or
volition.

II. 1.
Muscular motions excited by perpetual irritations occasionally become
obedient sensation and to volition. 2.
And the sensual motions.

III. 1. Other
muscular motions are associated with the irritative ones. 2. And other ideas with irritative ones. Of
letters, language, hieroglyphics. Irritative ideas exist without our
attention to them.

I. 1. Many of our
muscular motions are excited by perpetual irritations, as those of the
heart and arterial system by the circumfluent blood. Many other of them
are excited by intermitted irritations, as those of the stomach and
bowels by the aliment we swallow; of the bile-ducts by the bile; of the
kidneys, pancreas, and many other glands, by the peculiar fluids they
separate from the blood; and those of the lacteal and other absorbent
vessels by the chyle, lymph, and moisture of the atmosphere. These
motions are accelerated or retarded, as their correspondent irritations
are increased or diminished, without our attention or consciousness, in
the same manner as the various secretions of fruit, gum, resin, wax, and,
honey, are produced in the vegetable world, and as the juices of the
earth and the moisture of the atmosphere are absorbed by their roots and
foliage.

2. Other muscular motions, that are most
frequently connected with our sensations, as those of the sphincters of
the bladder and anus, and the musculi erectores penis, were originally
excited into motion by irritation, for young children make water, and
have other evacuations without attention to these circumstances; “et
primis etiam ab incunabulis tenduntur sæpius puerorum penes, amore nondum
expergefacto.” So the nipples of young women are liable to become turgid
by irritation, long before they are in a situation to be excited by the
pleasure of giving milk to the lips of a child.

3. The contractions of the larger muscles
of our bodies, that are most frequently connected with volition, were
originally excited into action by internal irritations: as appears from
the stretching or yawning of all animals after long sleep. In the
beginning of some fevers this irritation of the muscles produces
perpetual stretching and yawning; in other periods of fever an universal
restlessness arises from the same cause, the patient changing the
attitude of his body every minute. The repeated struggles of the
fœtus in the uterus must be owing to this internal irritation: for
the fœtus can have no other inducement to move its limbs but the
tædium or irksomeness of a continued posture.

The following case evinces, that the motions of stretching the limbs
after a continued attitude are not always owing to the power of the will.
Mr. Dean, a mason, of Austry in Leicestershire, had the spine of the
third vertebra of the back enlarged; in some weeks his lower extremities
became feeble, and at length quite paralytic: neither the pain of
blisters, the heat of fomentations, nor the utmost efforts of the will
could produce the least motion in these limbs; yet twice or thrice a day
for many months his feet, legs, and thighs, were affected for many
minutes with forceable stretchings, attended with the sensation of
fatigue; and he at length recovered the use of his limbs, though the
spine continued protuberant. The same circumstance is frequently seen in
a less degree in the common hemiplagia; and when this happens, I have
believed repeated and strong shocks of electricity to have been of great
advantage.

4. In like manner the various organs of
sense are originally excited into motion by various external stimuli
adapted to this purpose, which motions are termed perceptions or ideas;
and many of these motions during our waking hours are excited by
perpetual irritation, as those of the organs of hearing and of touch. The
former by the constant low indistinct noises that murmur around us, and
the latter by the weight of our bodies on the parts which support them;
and by the unceasing variations of the heat, moisture, and pressure of
the atmosphere; and these sensual motions, precisely as the muscular ones
above mentioned, obey their correspondent irritations without our
attention or consciousness.

5. Other classes of our ideas are more
frequently excited by our sensations of pleasure or pain, and others by
volition: but that these have all been originally excited by stimuli from
external objects, and only vary in their combinations or reparations, has
been fully evinced by Mr. Locke: and are by him termed the ideas of
perception in contradistinction to those, which he calls the ideas of
reflection.

II. 1. These
muscular motions, that are excited by perpetual irritation, are
nevertheless occasionally excitable by the sensations of pleasure or
pain, or by volition; as appears by the palpitation of the heart from
fear, the increased secretion of saliva at the sight of agreeable food,
and the glow on the skin of those who are ashamed. There is an instance
told in the Philosophical Transactions of a man, who could for a time
stop the motion of his heart when he pleased; and Mr. D. has often told
me, be could so far increase the peristaltic motion of his bowels by
voluntary efforts, as to produce an evacuation by stool at any time in
half an hour.

2. In like manner the sensual motions, or
ideas, that are excited by perpetual irritation, are nevertheless
occasionally excited by sensation or volition; as in the night, when we
listen under the influence of fear, or from voluntary attention, the
motions excited in the organ of hearing by the whispering of the air in
our room, the pulsation of our own arteries, or the faint beating of a
distant watch, become objects of perception.

III. 1.
Innumerable trains or tribes of other motions are associated with these
muscular motions which are excited by irritation; as by the stimulus of
the blood in the right chamber of the heart, the lungs are induced to
expand themselves; and the pectoral and intercostal muscles, and the
diaphragm, act at the same time by their associations with them. And when
the pharinx is irritated by agreeable food, the muscles of deglutition
are brought into action by association. Thus when a greater light falls
on the eye, the iris is brought into action without our attention; and
the ciliary process, when the focus is formed before or behind the
retina, by their associations with the increased irritative motions of
the organ of vision. Many common actions of life are produced in a
similar manner. If a fly settle on my forehead, whilst I am intent on my
present occupation, I dislodge it with my finger, without exciting my
attention or breaking the train of my ideas.

2. In like manner the irritative ideas
suggest to us many other trains or tribes of ideas that are associated
with them. On this kind of connection, language, letters, hieroglyphics,
and every kind of symbol, depend. The symbols themselves produce
irritative ideas, or sensual motions, which we do not attend to; and
other ideas, that are succeeded by sensation, are excited by their
association with them. And as these irritative ideas make up a part of
the chain of our waking thoughts, introducing other ideas that engage our
attention, though themselves are unattended to, we find it very difficult
to investigate by what steps many of our hourly trains of ideas gain
their admittance.

It may appear paradoxical, that ideas can exist, and not be attended
to; but all our perceptions are ideas excited by irritation, and
succeeded by sensation. Now when these ideas excited by irritation give
us neither pleasure nor pain, we cease to attend to them. Thus whilst I
am walking through that grove before my window, I do not run against the
trees or the benches, though my thoughts are strenuously exerted on some
other object. This leads us to a distinct knowledge of irritative ideas,
for the idea of the tree or bench, which I avoid, exists on my retina,
and induces by association the action of certain locomotive muscles;
though neither itself nor the actions of those muscles engage my
attention.

Thus whilst we are conversing on this subject, the tone, note, and
articulation of every individual word forms its correspondent irritative
idea on the organ of hearing; but we only attend to the associated ideas,
that are attached by habit to these irritative ones, and are succeeded by
sensation; thus when we read the words “PRINTING-PRESS” we do not attend to the shape, size, or
existence of the letters which compose these words, though each of them
excites a correspondent irritative motion of our organ of vision, but
they introduce by association our idea of the most useful of modern
inventions; the capacious reservoir of human knowledge, whose branching
streams diffuse sciences, arts, and morality, through all nations and all
ages.

SECT. VIII.

OF SENSITIVE MOTIONS.

I. 1.
Sensitive muscular motions were originally excited into action by
irritation. 2. And sensitive sensual
motions, ideas of imagination, dreams. II.
1. Sensitive muscular motions are
occasionally obedient to volition. 2.
And sensitive sensual motions. III. 1. Other muscular motions are associated
with the sensitive ones. 2. And other
sensual motions.

I. 1. Many of
the motions of our muscles, that are excited into action by irritation,
are at the same time accompanied with painful or pleasurable sensations;
and at length become by habit causable by the sensations. Thus the
motions of the sphincters of the bladder and anus were originally excited
into action by irritation; for young children give no attention to these
evacuations; but as soon as they become sensible of the inconvenience of
obeying these irritations, they suffer the water or excrement to
accumulate, till it disagreeably affects them; and the action of those
sphincters is then in consequence of this disagreeable sensation. So the
secretion of saliva, which in young children is copiously produced by
irritation, and drops from their mouths, is frequently attended with the
agreeable sensation produced by the mastication of tasteful food;, till
at length the sight of such food to a hungry person excites into action
these salival glands; as is seen in the slavering of hungry dogs.

The motions of those muscles, which are affected by lascivious ideas,
and those which are exerted in smiling, weeping, starting from fear, and
winking at the approach of danger to the eye, and at times the actions of
every large muscle of the body become causable by our sensations. And all
these motions are performed with strength and velocity in proportion to
the energy of the sensation that excites them, and the quantity of
sensorial power.

2. Many of the motions of our organs of
sense, or ideas, that were originally excited into action by irritation,
become in like manner more frequently causable by our sensations of
pleasure or pain. These motions are then termed the ideas of imagination,
and make up all the scenery and transactions of our dreams. Thus when any
painful or pleasurable sensations possess us, as of love, anger, fear;
whether in our sleep or waking hours, the ideas, that have been formerly
excited by the objects of these sensations, now vividly recur before us
by their connection with these sensations themselves. So the fair smiling
virgin, that excited your love by her presence, whenever that sensation
recurs, rises before you in imagination; and that with all the pleasing
circumstances, that had before engaged your attention. And in sleep, when
you dream under the influence of fear, all the robbers, fires, and
precipices, that you formerly have seen or heard of, arise before you
with terrible vivacity. All these sensual motions, like the muscular ones
above mentioned, are performed with strength and velocity in proportion
to the energy of the sensation of pleasure or pain, which excites them,
and the quantity of sensorial power.

II. 1. Many of
these muscular motions above described, that are most frequently excited
by our sensations, are nevertheless occasionally causable by volition;
for we can smile or frown spontaneously, can make water before the
quantity or acrimony of the urine produces a disagreeable sensation, and
can voluntarily masticate a nauseous drug, or swallow a bitter draught,
though our sensation would strongly dissuade us.

2. In like manner the sensual motions, or
ideas, that are most frequently excited by our sensations, are
nevertheless occasionally causeable by volition, as we can spontaneously
call up our last night’s dream before us, tracing it industriously step
by step through all its variety of scenery and transaction; or can
voluntarily examine or repeat the ideas, that have been excited by out
disgust or admiration.

III. 1.
Innumerable trains or tribes of motions are associated with these
sensitive muscular motions above mentioned; as when a drop of water
falling into the wind-pipe disagreeably affects the air-vessels of the
lungs, they are excited into violent action; and with these sensitive
motions are associated the actions of the pectoral and intercostal
muscles, and the diaphragm; till by their united and repeated succussions
the drop is returned through the larinx. The same occurs when any thing
disagreeably affects the nostrils, or the stomach, or the uterus; variety
of muscles are excited by association into forcible action, not to be
suppressed by the utmost efforts of the will; as in sneezing, vomiting,
and parturition.

2. In like manner with these sensitive
sensual motions, or ideas of imagination, are associated many other
trains or tribes of ideas, which by some writers of metaphysics have been
classed under the terms of resemblance, causation, and contiguity; and
will be more fully treated of hereafter.

SECT. IX.

OF VOLUNTARY MOTIONS.

I. 1. Voluntary
muscular motions are originally excited by irritations. 2. And voluntary ideas. Of reason. II. 1. Voluntary
muscular motions are occasionally causable by sensations. 2. And voluntary ideas. III. 1. Voluntary
muscular motions are occasionally obedient to irritations. 2. And voluntary ideas. IV. 1. Voluntary
muscular motions are associated with other muscular motions. 2. And voluntary ideas.

When pleasure or pain affect the animal system, many of its motions
both muscular and sensual are brought into action; as was shewn in the
preceding section, and were called sensitive motions. The general
tendency of these motions is to arrest and to possess the pleasure, or to
dislodge or avoid the pain: but if this cannot immediately be
accomplished, desire or aversion are produced, and the motions in
consequence of this new faculty of the sensorium are called
voluntary.

I. 1. Those muscles
of the body that are attached to bones, have in general their principal
connections with volition, as I move my pen or raise my body. These
motions were originally excited by irritation, as was explained in the
section on that subject, afterwards the sensations of pleasure or pain,
that accompanied the motions thus excited, induced a repetition of them;
and at length many of them were voluntarily practised in succession or in
combination for the common purposes of life, as in learning to walk, or
to speak; and are performed with strength and velocity in proportion to
the energy of the volition, that excites them, and the quantity of
sensorial power.

2. Another great class of voluntary motions
consists of the ideas of recollection. We will to repeat a certain train
of ideas, as of the alphabet backwards; and if any ideas, that do not
belong to this intended train, intrude themselves by other connections,
we will to reject them, and voluntarily persist in the determined train.
So at my approach to a house which I have but once visited, and that at
the distance of many months, I will to recollect the names of the
numerous family I expect to see there, and I do recollect them.

On this voluntary recollection of ideas our faculty of reason depends,
as it enables us to acquire an idea of the dissimilitude of any two
ideas. Thus if you voluntarily produce the idea of a right-angled
triangle, and then of a square; and after having excited these ideas
repeatedly, you excite the idea of their difference, which is that of
another right-angled triangle inverted over the former; you are said to
reason upon this subject, or to compare your ideas.

These ideas of recollection, like the muscular motions above
mentioned, were originally excited by the irritation of external bodies,
and were termed ideas of perception: afterwards the pleasure or pain,
that accompanied these motions, induced a repetition of them in the
absence of the external body, by which they were first excited; and then
they were termed ideas of imagination. At length they become voluntarily
practised in succession or in combination for the common purposes of
life; as when we make ourselves masters of the history of mankind, or of
the sciences they have investigated; and are then called ideas of
recollection; and are performed with strength and velocity in proportion
to the energy of the volition that excites them, and the quantity of
sensorial power.

II. 1. The muscular
motions above described, that are most frequently obedient to the will
are nevertheless occasionally causable by painful or pleasurable
sensation, as in the starting from fear, and the contraction of the calf
of the leg in the cramp.

2. In like manner the sensual motions, or
ideas, that are most frequently connected with volition, are nevertheless
occasionally causable by painful or pleasurable sensation. As the
histories of men, or the description of places, which we have voluntarily
taken pains to remember, sometimes occur to us in our dreams.

III. 1. The muscular
motions that are generally subservient to volition, are also occasionally
causable by irritation, as in stretching the limbs after sleep, and
yawning. In this manner a contraction of the arm is produced by passing
the electric fluid from the Leyden phial along its muscles; and that even
though the limb is paralytic. The sudden motion of the arm produces a
disagreeable sensation in the joint, but the muscles seem to be brought
into action simply by irritation.

2. The ideas, that are generally subservient
to the will, are in like manner occasionally excited by irritation; as
when we view again an object, we have before well studied, and often
recollected.

IV. 1. Innumerable
trains or tribes of motions are associated with these voluntary muscular
motions above mentioned; as when I will to extend my arm to a distant
object, some other muscles are brought into action, and preserve the
balance of my body. And when I wish to perform any steady exertion, as in
threading a needle, or chopping with an ax, the pectoral muscles are at
the same time brought into action to preserve the trunk of the body
motionless, and we cease to respire for a time.

2. In like manner the voluntary sensual
motions, or ideas of recollection, are associated with many other trains
or tribes of ideas. As when I voluntarily recollect a gothic window, that
I saw some time ago, the whole front of the cathedral occurs to me at the
same time.

SECT. X.

OF ASSOCIATE MOTIONS.

I. 1. Many
muscular motions excited by irritations in trains or tribes become
associated. 2. And many ideas. II. 1. Many sensitive
muscular motions become associated. 2.
And many sensitive ideas. III. 1. Many voluntary muscular motions become
associated. 2. And then become obedient
to sensation or irritation. 3. And many
voluntary ideas become associated.

All the fibrous motions, whether muscular or sensual, which are
frequently brought into action together, either in combined tribes, or in
successive trains, become so connected by habit, that when one of them is
reproduced the others have a tendency to succeed or accompany it.

I. 1. Many of our
muscular motions were originally excited in successive trains, as the
contractions of the auricles and of the ventricles of the heart; and
others in combined tribes, as the various divisions of the muscles which
compose the calf of the leg, which were originally irritated into
synchronous action by the tædium or irksomeness of a continued posture.
By frequent repetitions these motions acquire associations, which
continue during our lives, and even after the destruction of the greatest
part of the sensorium; for the heart of a viper or frog will continue to
pulsate long after it is taken from the body; and when it has entirely
ceased to move, if any part of it is goaded with a pin, the whole heart
will again renew its pulsations. This kind of connection we shall term
irritative association, to distinguish it from sensitive and voluntary
associations.

2. In like manner many of our ideas are
originally excited in tribes; as all the objects of sight, after we
become so well acquainted with the laws of vision, as to distinguish
figure and distance as well as colour; or in trains, as while we pass
along the objects that surround us. The tribes thus received by
irritation become associated by habit, and have been termed complex ideas
by the writers of metaphysics, as this book, or that orange. The trains
have received no particular name, but these are alike associations of
ideas, and frequently continue during our lives. So the taste of a
pine-apple, though we eat it blindfold, recalls the colour and shape of
it; and we can scarcely think on solidity without figure.

II. 1. By the various
efforts of our sensations to acquire or avoid their objects, many muscles
are daily brought into successive or synchronous actions; these become
associated by habit, and are then excited together with great facility,
and in many instances gain indissoluble connections. So the play of
puppies and kittens is a representation of their mode of fighting or of
taking their prey; and the motions of the muscles necessary for those
purposes become associated by habit, and gain a great adroitness of
action by these early repetitions: so the motions of the abdominal
muscles, which were originally brought into concurrent action, with the
protrusive motion of the rectum or bladder by sensation, become so
conjoined with them by habit, that they not only easily obey these
sensations occasioned by the stimulus of the excrement and urine, but are
brought into violent and unrestrainable action in the strangury and
tenesmus. This kind of connection we shall term sensitive
association.

2. So many of our ideas, that have been
excited together or in succession by our sensations, gain synchronous or
successive associations, that are sometimes indissoluble but with life.
Hence the idea of an inhuman or dishonourable action perpetually calls up
before us the idea of the wretch that was guilty of it. And hence those
unconquerable antipathies are formed, which some people have to the sight
of peculiar kinds of food, of which in their infancy they have eaten to
excess or by constraint.

III. 1. In learning
any mechanic art, as music, dancing, or the use of the sword, we teach
many of our muscles to act together or in succession by repeated
voluntary efforts; which by habit become formed into tribes or trains of
association, and serve all our purposes with great facility, and in some
instances acquire an indissoluble union. These motions are gradually
formed into a habit of acting together by a multitude of repetitions,
whilst they are yet separately causable by the will, as is evident from
the long time that is taken up by children in learning to walk and to
speak; and is experienced by every one, when he first attempts to skate
upon the ice or to swim: these we shall term voluntary associations.

2. All these muscular movements, when they
are thus associated into tribes or trains, become afterwards not only
obedient to volition, but to the sensations and irritations; and the same
movement composes a part of many different tribes or trains of motion.
Thus a single muscle, when it acts in consort with its neighbours on one
side, assists to move the limb in one direction; and in another, when, it
acts with those in its neighbourhood on the other side; and in other
directions, when it acts separately or jointly with those that lie
immediately under or above it; and all these with equal facility after
their associations have been well established.

The facility, with which each muscle changes from one associated tribe
to another, and that either backwards or forwards, is well observable in
the muscles of the arm in moving the windlass of an air-pump; and the
slowness of those muscular movements, that have not been associated by
habit, may be experienced by any one, who shall attempt to saw the air
quick perpendicularly with one hand, and horizontally with the other at
the same time.

3. In learning every kind of science we
voluntarily associate many tribes and trains of ideas, which afterwards
are ready for all the purposes either of volition, sensation, or
irritation; and in some instances acquire indissoluble habits of acting
together, so as to affect our reasoning, and influence our actions. Hence
the necessity of a good education.

These associate ideas are gradually formed into habits of acting
together by frequent repetition, while they are yet separately obedient
to the will; as is evident from the difficulty we experience in gaining
so exact an idea of the front of St. Paul’s church, as to be able to
delineate it with accuracy, or in recollecting a poem of a few pages.

And these ideas, thus associated into tribes, not only make up the
parts of the trains of volition, sensation, and irritation; but the same
idea composes a part of many different tribes and trains of ideas. So the
simple idea of whiteness composes a part of the complex idea of snow,
milk, ivory; and the complex idea of the letter A composes a part of the
several associated trains of ideas that make up the variety of words, in
which this letter enters.

The numerous trains of these associated ideas are divided by Mr. Hume
into three classes, which he has termed contiguity, causation, and
resemblance. Nor should we wonder to find them thus connected together,
since it is the business of our lives to dispose them into those three
classes; and we become valuable to ourselves and our friends, as we
succeed in it. Those who have combined an extensive class of ideas by the
contiguity of time or place, are men learned in the history of mankind,
and of the sciences they have cultivated. Those who have connected a
great class of ideas of resemblances, possess the source of the ornaments
of poetry and oratory, and of all rational analogy. While those who have
connected great classes of ideas of causation, are furnished with the
powers of producing effects. These are the men of active wisdom, who lead
armies to victory, and kingdoms to prosperity; or discover and improve
the sciences, which meliorate and adorn the condition of humanity.

SECT. XI.

ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS.

I. Stimulation is of various kinds adapted
to the organs of sense, to the muscles, to hollow membranes, and glands.
Some objects irritate our senses by repeated impulses. II. 1. Sensation and
volition frequently affect the whole sensorium. 2. Emotions, passions, appetites. 3. Origin of desire and aversion. Criterion of
voluntary actions, difference of brutes and men. 4. Sensibility and voluntarity. III. Associations formed before nativity,
irritative motions mistaken for officiated ones.

Irritation.

I. The various organs of sense require various
kinds of stimulation to excite them into action; the particles of light
penetrate the cornea and humours of the eye, and then irritate the naked
retina; rapid particles, dissolved or diffused in water or saliva, and
odorous ones, mixed or combined with the air, irritate the extremities of
the nerves of taste and smell; which either penetrate, or are expanded on
the membranes of the tongue and nostrils; the auditory nerves are
stimulated by the vibrations of the atmosphere communicated by means of
the tympanum and of the fluid, whether of air or of water, behind it; and
the nerves of touch by the hardness of surrounding bodies, though the
cuticle is interposed between these bodies and the medulla of the
nerve.

As the nerves of the senses have each their appropriated objects,
which stimulate them into activity; so the muscular fibres, which are the
terminations of other sets of nerves, have their peculiar objects, which
excite them into action; the longitudinal muscles are stimulated into
contraction by extension, whence the stretching or pandiculation after a
long continued posture, during which they have been kept in a state of
extension; and the hollow muscles are excited into action by distention,
as those of the rectum and bladder are induced to protrude their contents
from their sense of the distention rather than of the acrimony of those
contents.

There are other objects adapted to stimulate the nerves, which
terminate in variety of membranes, and those especially which form the
terminations of canals; thus the preparations of mercury particularly
affect the salivary glands, ipecacuanha the stomach, aloe the sphincter
of the anus, cantharides that of the bladder, and lastly every gland of
the body appears to be indued with a kind of taste, by which it selects
or forms each its peculiar fluid from the blood; and by which it is
irritated into activity.

Many of these external properties of bodies, which stimulate our
organs of sense, do not seem to effect this by a single impulse, but by
repeated impulses; as the nerve of the ear is probably not excitable by a
single vibration of air, nor the optic nerve by a single particle of
light; which circumstance produces some analogy between those two senses,
at the same time the solidity of bodies is perceived by a single
application of a solid body to the nerves of touch, and that even through
the cuticle; and we are probably possessed of a peculiar sense to
distinguish the nice degrees of heat and cold.

The senses of touch and of hearing acquaint us with the mechanical
impact and vibration of bodies, those of smell and taste seem to acquaint
us with some of their chemical properties, while the sense of vision and
of heat acquaint us with the existence of their peculiar fluids.

Sensation and Volition.

II. Many motions are produced by pleasure or
pain, and that even in contradiction to the power of volition, as in
laughing, or in the strangury; but as no name has been given to pleasure
or pain, at the time it is exerted so as to cause fibrous motions, we
have used the term sensation for this purpose; and mean it to bear the
same analogy to pleasure and pain, that the word volition does to desire
and aversion.

1. It was mentioned in the fifth Section,
that, what we have termed sensation is a motion of the central parts, or
of the whole sensorium, beginning at some of the extremities of
it. This appears first, because our pains and pleasures are always caused
by our ideas or muscular motions, which are the motions of the
extremities of the sensorium. And, secondly, because the sensation of
pleasure or pain frequently continues some time after the ideas or
muscular motions which excited it have ceased: for we often feel a glow
of pleasure from an agreeable reverie, for many minutes after the ideas,
that were the subject of it, have escaped our memory; and frequently
experience a dejection of spirits without being able to assign the cause
of it but by much recollection.

When the sensorial faculty of desire or aversion is exerted so as to
cause fibrous motions, it is termed volition; which is said in Sect. V. to be a motion of the central parts, or of the
whole sensorium, terminating in some of the extremities of it.
This appears, first, because our desires and aversions always terminate
in recollecting and comparing our ideas, or in exerting our muscles;
which are the motions of the extremities of the sensorium. And, secondly,
because desire or aversion begins, and frequently continues for a time in
the central parts of the sensorium, before it is peculiarly exerted at
the extremities of it; for we sometimes feel desire or aversion without
immediately knowing their objects, and in consequence without immediately
exerting any of our muscular or sensual motions to attain them: as in the
beginning of the passion of love, and perhaps of hunger, or in the ennui
of indolent people.

Though sensation and volition begin or terminate at the extremities or
central parts of the sensorium, yet the whole of it is frequently
influenced by the exertion of these faculties, as appears from their
effects on the external habit: for the whole skin is reddened by shame,
and an universal trembling is produced by fear: and every muscle of the
body is agitated in angry people by the desire of revenge.

There is another very curious circumstance, which shews that sensation
and volition are movements of the sensorium in contrary directions; that
is, that volition begins at the central parts of it, and proceeds to the
extremities; and that sensation begins at the extremities, and proceeds
to the central parts: I mean that these two sensorial faculties cannot be
strongly exerted at the same time; for when we exert our volition
strongly, we do not attend to pleasure or pain; and conversely, when we
are strongly affected with the sensation of pleasure or pain, we use no
volition. As will be further explained in Section XVIII. on sleep, and Section XXXIV. on volition.

2. All our emotions and passions seem to
arise out of the exertions of these two faculties of the animal
sensorium. Pride, hope, joy, are the names of particular pleasures:
shame, despair, sorrow, are the names of peculiar pains: and love,
ambition, avarice, of particular desires: hatred, disgust, fear, anxiety,
of particular aversions. Whilst the passion of anger includes the pain
from a recent injury, and the aversion to the adversary that occasioned
it. And compassion is the pain we experience at the sight of misery, and
the desire of relieving it.

There is another tribe of desires, which are commonly termed
appetites, and are the immediate consequences of the absence of some
irritative motions. Those, which arise from defect of internal
irritations, have proper names conferred upon them, as hunger, thirst,
lust, and the desire of air, when our respiration is impaired by noxious
vapours; and of warmth, when we are exposed to too great a degree of
cold. But those, whose stimuli are external to the body, are named from
the objects, which are by nature constituted to excite them; these
desires originate from our past experience of the pleasurable sensations
they occasion, as the smell of an hyacinth, or the taste of a
pine-apple.

Whence it appears, that our pleasures and pains are at least as
various and as numerous as our irritations; and that our desires and
aversions must be as numerous as our pleasures and pains. And that as
sensation is here used as a general term for our numerous pleasures and
pains, when they produce the contractions of our fibres; so volition is
the general name for our desires and aversions, when they produce fibrous
contractions. Thus when a motion of the central parts, or of the whole
sensorium, terminates in the exertion of our muscles, it is generally
called voluntary action; when it terminates in the exertion of our ideas,
it is termed recollection, reasoning, determining.

3. As the sensations of pleasure and pain
are originally introduced by the irritations of external objects: so our
desires and aversions are originally introduced by those sensations; for
when the objects of our pleasures or pains are at a distance, and we
cannot instantaneously possess the one, or avoid the other, then desire
or aversion is produced, and a voluntary exertion of our ideas or muscles
succeeds.

The pain of hunger excites you to look out for food, the tree, that
shades you, presents its odoriferous fruit before your eyes, you
approach, pluck, and eat.

The various movements of walking to the tree, gathering the fruit, and
masticating it, are associated motions introduced by their connection
with sensation; but if from the uncommon height of the tree, the fruit be
inaccessible, and you are prevented from quickly possessing the intended
pleasure, desire is produced. The consequence of this desire is, first, a
deliberation about the means to gain the object of pleasure in process of
time, as it cannot be procured immediately; and, secondly, the muscular
action necessary for this purpose.

You voluntarily call up all your ideas of causation, that are related
to the effect you desire, and voluntarily examine and compare them, and
at length determine whether to ascend the tree, or to gather stones from
the neighbouring brook, is easier to practise, or more promising of
success; and, finally, you gather the stones, and repeatedly fling them
to dislodge the fruit.

Hence then we gain a criterion to distinguish voluntary acts or
thoughts from those caused by sensation. As the former are always
employed about the means to acquire pleasurable objects, or the
means to avoid painful ones; while the latter are employed in the
possession of those, which are already in our power.

Hence the activity of this power of volition produces the great
difference between the human and the brute creation. The ideas and the
actions of brutes are almost perpetually employed about their present
pleasures, or their present pains; and, except in the few instances which
are mentioned in Section XVI, on instinct, they
seldom busy themselves about the means of procuring future bliss, or of
avoiding future misery; so that the acquiring of languages, the making of
tools, and labouring for money, which are all only the means to procure
pleasures; and the praying to the Deity, as another means to procure
happiness, are characteristic of human nature.

4. As there are many diseases produced by
the quantity of the sensation of pain or pleasure being too great or too
little; so are there diseases produced by the susceptibility of the
constitution to motions causable by these sensations being too dull or
too vivid. This susceptibility of the system to sensitive motions is
termed sensibility, to distinguish it from sensation, which is the actual
existence or exertion of pain or pleasure.

Other classes of diseases are owing to the excessive promptitude, or
sluggishness of the constitution to voluntary exertions, as well as to
the quantity of desire or of aversion. This susceptibility of the system
to voluntary motions is termed voluntarity, to distinguish it from
volition, which is the exertion of desire or aversion; these diseases
will be treated of at length in the progress of the work.

Association.

III. 1. It is not
easy to assign a cause, why those animal movements, that have once
occurred in succession, or in combination, should afterwards have a
tendency to succeed or accompany each other. It is a property of
animation, and distinguishes this order of being from the other
productions of nature.

When a child first wrote the word man, it was distinguished in his
mind into three letters, and those letters into many parts of letters;
but by repeated use the word man becomes to his hand in writing it, as to
his organs of speech in pronouncing it, but one movement without any
deliberation, or sensation, or irritation, interposed between the parts
of it. And as many separate motions of our muscles thus become united,
and form, as it were, one motion; so each separate motion before such
union may be conceived to consist of many parts or spaces moved through;
and perhaps even the individual fibres of our muscles have thus gradually
been brought to act in concert, which habits began to be acquired as
early as the very formation of the moving organs, long before the
nativity of the animal; as explained in the Section XVI. 2. on instinct.

2. There are many motions of the body,
belonging to the irritative class, which might by a hasty observer be
mistaken for associated ones; as the peristaltic motion of the stomach
and intestines, and the contractions of the heart and arteries, might be
supposed to be associated with the irritative motions of their nerves of
sense, rather than to be excited by the irritation of their muscular
fibres by the distention, acrimony, or momentum of the blood. So the
distention or elongation of muscles by objects external to them irritates
them into contraction, though the cuticle or other parts may intervene
between the stimulating body and the contracting muscle. Thus a horse
voids his excrement when its weight or bulk irritates the rectum or
sphincter ani. These muscles act from the irritation of distention, when
he excludes his excrement, but the muscles of the abdomen and diaphragm
are brought into motion by association with those of the sphincter and
rectum.

SECT. XII.

OF STIMULUS, SENSORIAL EXERTION, AND FIBROUS CONTRACTION.

I. Of fibrous contraction. 1. Two particles of a fibre cannot approach
without the intervention of something, as in magnetism, electricity,
elasticity. Spirit of life is not electric ether. Galvani’s
experiments. 2. Contraction of a
fibre. 3. Relaxation succeeds. 4. Successive contractions, with intervals.
Quick pulse from debility, from paucity of blood. Weak contractions
performed in less time, and with shorter intervals. 5. Last situation of the fibres continues
after contraction. 6. Contraction
greater than usual induces pleasure or pain. 7. Mobility of the fibres uniform. Quantity
of sensorial power fluctuates. Constitutes excitability. II. Of sensorial exertion. 1. Animal motion includes stimulus, sensorial
power, and contractile fibres. The sensorial faculties act separately or
conjointly. Stimulus of four kinds. Strength and weakness defined.
Sensorial power perpetually exhausted and renewed. Weakness from defect
of stimulus. From defect of sensorial power, the direct and indirect
debility of Dr. Brown. Why we become warm in Buxton bath after a time,
and see well after a time in a darkish room. Fibres may act violently, or
with their whole force, and yet feebly. Great exertion in inflammation
explained. Great muscular force of some insane people. 2. Occasional accumulation of sensorial power
in muscles subject to constant stimulus. In animals sleeping in winter.
In eggs, seeds, schirrous tumours, tendons, bones. 3. Great exertion introduces pleasure or
pain. Inflammation. Libration of the system between torpor and activity.
Fever-fits. 4. Desire and aversion
introduced. Excess of volition cures fevers. III. Of repeated stimulus. 1. A stimulus repeated too frequently looses
effect. As opium, wine, grief. Hence old age. Opium and aloes in small
doses. 2. A stimulus not repeated too
frequently does not lose effect. Perpetual movement of the vital
organs. 3. A stimulus repeated at
uniform times produces greater effect. Irritation combined with
association. 4. A stimulus repeated
frequently and uniformly may be withdrawn, and the action of the organ
will continue. Hence the bark cures agues, and strengthens weak
constitutions. 5. Defect of stimulus
repeated at certain intervals causes fever-fits. 6. Stimulus long applied ceases to act a
second time. 7. If a stimulus excites
sensation in an organ not usually excited into sensation, inflammation is
produced. IV. Of stimulus greater than
natural. 1. A stimulus greater than
natural diminishes the quantity of sensorial power in general. 2. In particular organs. 3. Induces the organ into spasmodic
actions. 4. Induces the antagonist
fibres into action. 5. Induces the
organ into convulsive or fixed spasms. 6.
Produces paralysis of the organ. V. Of
stimulus less than natural. 1. Stimulus
less than natural occasions accumulation of sensorial power in
general. 2. In particular organs,
flushing of the face in a frosty morning. In fibres subject to perpetual
stimulus only. Quantity of sensorial power inversely as the stimulus.
3. Induces pain. As of cold, hunger,
head-ach. 4. Induces more feeble and
frequent contraction. As in low fevers. Which are frequently owing to
deficiency of sensorial power rather than to deficiency of stimulus.
5. Inverts successive trains of motion.
Inverts ideas. 6. Induces paralysis
and death. VI. Cure of increased exertion.
1. Natural cure of exhaustion of sensorial
power. 2. Decrease the irritations.
Venesection. Cold. Abstinence. 3.
Prevent the previous cold fit. Opium. Bark. Warmth. Anger.
Surprise. 4. Excite some other part of
the system. Opium and warm bath relieve pains both from defect and from
excess of stimulus. 5. First increase
the stimulus above, and then decrease it beneath the natural
quantity. VII. Cure of decreased exertion.
1. Natural cure by accumulation of
sensorial power. Ague-fits. Syncope. 2.
Increase the stimulation, by wine, opium, given so as not to
intoxicate. Cheerful ideas. 3. Change
the kinds of stimulus. 4. Stimulate
the associated organs. Blisters of use in heart-burn, and cold
extremities. 5. Decrease the
stimulation for a time, cold bath. 6.
Decrease the stimulation below natural, and then increase it above
natural. Bark after emetics. Opium after venesection. Practice of
Sydenham in chlorosis. 7. Prevent
unnecessary expenditure of sensorial power. Decumbent posture, silence,
darkness. Pulse quickened by rising out of bed. 8. To the greatest degree of quiescence apply
the least stimulus. Otherwise paralysis or inflammation of the organ
ensues. Gin, wine, blisters, destroy by too great stimulation in fevers
with debility. Intoxication in the slightest degree succeeded by
debility. Golden rule for determining the best degree of stimulus in low
fevers. Another golden rule for determining the quantity of spirit which
those, who are debilitated by drinking it, may safely omit.

I. Of fibrous contraction.

1. If two particles of iron lie near each
other without motion, and afterwards approach each other; it is
reasonable to conclude that something besides the iron particles is the
cause of their approximation; this invisible something is termed
magnetism. In the same manner, if the particles, which compose an animal
muscle, do not touch each other in the relaxed state of the muscle, and
are brought into contact during the contraction of the muscle, it is
reasonable to conclude, that some other agent is the cause of this new
approximation. For nothing can act, where it does not exist; for to act
includes to exist; and therefore the particles of the muscular fibre
(which in its state of relaxation are supposed not to touch) cannot
affect each other without the influence of some intermediate agent; this
agent is here termed the spirit of animation, or sensorial power, but may
with equal propriety be termed the power, which causes contraction; or
may be called by any other name, which the reader may choose to affix to
it.

The contraction of a muscular fibre may be compared to the following
electric experiment, which is here mentioned not as a philosophical
analogy, but as an illustration or simile to facilitate the conception of
a difficult subject. Let twenty very small Leyden phials properly coated
be hung in a row by fine silk threads at a small distance from each
other; let the internal charge of one phial be positive, and of the other
negative alternately, if a communication be made from the internal
surface of the first to the external surface of the last in the row, they
will all of them instantly approach each other, and thus shorten a line
that might connect them like a muscular fibre. See Botanic Garden, p. 1.
Canto I. 1. 202, note on Gymnotus.

The attractions of electricity or of magnetism do not apply
philosophically to the illustration of the contraction of animal fibres,
since the force of those attractions increases in some proportion
inversely as the distance, but in muscular motion there appears no
difference in velocity or strength during the beginning or end of the
contraction, but what may be clearly ascribed to the varying mechanic
advantage in the approximation of one bone to another. Nor can muscular
motion be assimilated with greater plausibility to the attraction of
cohesion or elasticity; for in bending a steel spring, as a small sword,
a less force is required to bend it the first inch than the second; and
the second than the third; the particles of steel on the convex side of
the bent spring endeavouring to restore themselves more powerfully the
further they are drawn from each other. See Botanic Garden, P. I. addit.
Note XVIII.

I am aware that this may be explained another way, by supposing the
elasticity of the spring to depend more on the compression of the
particles on the concave side than on the extension of them on the convex
side; and by supposing the elasticity of the elastic gum to depend more
on the resistance to the lateral compression of its particles than to the
longitudinal extension of them. Nevertheless in muscular contraction, as
above observed, there appears no difference in the velocity or force of
it at its commencement or at its termination; from whence we must
conclude that animal contraction is governed by laws of its own, and not
by those of mechanics, chemistry, magnetism, or electricity.

On these accounts I do not think the experiments conclusive, which
were lately published by Galvani, Volta, and others, to shew a similitude
between the spirit of animation, which contracts the muscular fibres, and
the electric fluid. Since the electric fluid may act only as a more
potent stimulus exciting the muscular fibres into action, and not by
supplying them with a new quantity of the spirit of life. Thus in a
recent hemiplegia I have frequently observed, when the patient yawned and
stretched himself, that the paralytic limbs moved also, though they were
totally disobedient to the will. And when he was electrified by passing
shocks from the affected hand to the affected foot, a motion of the
paralytic limbs was also produced. Now as in the act of yawning the
muscles of the paralytic limbs were excited into action by the stimulus
of the irksomeness of a continued posture, and not by any additional
quantity of the spirit of life; so we may conclude, that the passage of
the electric fluid, which produced a similar effect, acted only as a
stimulus, and not by supplying any addition of sensorial power.

If nevertheless this theory should ever become established, a stimulus
must be called an eductor of vital ether; which stimulus may consist of
sensation or volition, as in the electric eel, as well as in the appulses
of external bodies; and by drawing off the charges of vital fluid may
occasion the contraction or motions of the muscular fibres, and organs of
sense.

2. The immediate effect of the action of
the spirit of animation or sensorial power on the fibrous parts of the
body, whether it acts in the mode of irritation, sensation, volition, or
association, is a contraction of the animal fibre, according to the
second law of animal causation. Sect. IV. Thus the
stimulus of the blood induces the contraction of the heart; the agreeable
taste of a strawberry produces the contraction of the muscles of
deglutition; the effort of the will contracts the muscles, which move the
limbs in walking; and by association other muscles of the trunk are
brought into contraction to preserve the balance of the body. The fibrous
extremities of the organs of sense have been shewn, by the ocular spectra
in Sect. III. to suffer similar contraction by
each of the above modes of excitation; and by their configurations to
constitute our ideas.

3. After animal fibres have for some time
been excited into contraction, a relaxation succeeds, even though the
exciting cause continues to act. In respect to the irritative motions
this is exemplified in the peristaltic contractions of the bowels; which
cease and are renewed alternately, though the stimulus of the aliment
continues to be uniformly applied; in the sensitive motions, as in
strangury, tenesmus, and parturition, the alternate contractions and
relaxations of the muscles exist, though the stimulus is perpetual. In
our voluntary exertions it is experienced, as no one can hang long by the
hands, however vehemently he wills so to do; and in the associate motions
the constant change of our attitudes evinces the necessity of relaxation
to those muscles, which have been long in action.

This relaxation of a muscle after its contraction, even though the
stimulus continues to be applied, appears to arise from the expenditure
or diminution of the spirit of animation previously resident in the
muscle, according to the second law of animal causation in Sect. IV. In those constitutions, which are termed weak,
the spirit of animation becomes sooner exhausted, and tremulous motions
are produced, as in the hands of infirm people, when they lift a cup to
their mouths. This quicker exhaustion of the spirit of animation is
probably owing to a less quantity of it residing in the acting fibres,
which therefore more frequently require a supply from the nerves, which
belong to them.

4. If the sensorial power continues to act,
whether it acts in the mode of irritation, sensation, volition, or
association, a new contraction of the animal fibre succeeds after a
certain interval; which interval is of shorter continuance in weak people
than in strong ones. This is exemplified in the shaking of the hands of
weak people, when they attempt to write. In a manuscript epistle of one
of my correspondents, which is written in a small hand, I observed from
four to six zigzags in the perpendicular stroke of every letter, which
shews that both the contractions of the fingers, and intervals between
them, must have been performed in very short periods of time.

The times of contraction of the muscles of enfeebled people being
less, and the intervals between those contractions being less also,
accounts for the quick pulse in fevers with debility, and in dying
animals. The shortness of the intervals between one contraction and
another in weak constitutions, is probably owing to the general
deficiency of the quantity of the spirit of animation, and that therefore
there is a less quantity of it to be received at each interval of the
activity of the fibres. Hence in repeated motions, as of the fingers in
performing on the harpsichord, it would at first sight appear, that
swiftness and strength were incompatible; nevertheless the single
contraction of a muscle is performed with greater velocity as well as
with greater force by vigorous constitutions, as in throwing a
javelin.

There is however another circumstance, which may often contribute to
cause the quickness of the pulse in nervous fevers, as in animals
bleeding to death in the slaughter-house; which is the deficient quantity
of blood; whence the heart is but half distended, and in consequence
sooner contracts. See Sect. XXXII. 2.
1.

For we must not confound frequency of repetition with quickness of
motion, or the number of pulsations with the velocity, with which the
fibres, which constitute the coats of the arteries, contract themselves.
For where the frequency of the pulsations is but seventy-five in a
minute, as in health; the contracting fibres, which constitute the sides
of the arteries, may move through a greater space in a given time, than
where the frequency of pulsation is one hundred and fifty in a minute, as
in some fevers with great debility. For if in those fevers the arteries
do not expand themselves in their diastole to more than half the usual
diameter of their diastole in health, the fibres which constitute their
coats, will move through a less space in a minute than in health, though
they make two pulsations for one.

Suppose the diameter of the artery during its systole to be one line,
and that the diameter of the same artery during its diastole is in health
is four lines, and in a fever with, great debility only two lines. It
follows, that the arterial fibres contract in health from a circle of
twelve lines in circumference to a circle of three lines in
circumference, that is they move through a space of nine lines in length.
While the arterial fibres in the fever with debility would twice contract
from a circle of six lines to a circle of three lines; that is while they
move through a space equal to six lines. Hence though the frequency of
pulsation in fever be greater as two to one, yet the velocity of
contraction in health is greater as nine to six, or as three to two.

On the contrary in inflammatory diseases with strength, as in the
pleurisy, the velocity of the contracting sides of the arteries is much
greater than in health, for if we suppose the number of pulsations in a
pleurisy to be half as much more than in health, that is as one hundred
and twenty to eighty, (which is about what generally happens in
inflammatory diseases) and if the diameter of the artery in diastole be
one third greater than in health, which I believe is near the truth, the
result will be, that the velocity of the contractile sides of the
arteries will be in a pleurisy as two and a half to one, compared to the
velocity of their contraction in a state of health, for if the
circumference of the systole of the artery be three lines, and the
diastole in health be twelve lines in circumference, and in a pleurisy
eighteen lines; and secondly, if the artery pulsates thrice in the
diseased state for twice in the healthy one, it follows, that the
velocity of contraction in the diseased state to that in the healthy
state will be forty-five to eighteen, or as two and a half to one.

From hence it would appear, that if we had a criterion to determine
the velocity of the arterial contractions, it would at the same time give
us their strength, and thus be of more service in distinguishing
diseases, than the knowledge of their frequency. As such a criterion
cannot be had, the frequency of pulsation, the age of the patient being
allowed for, will in some measure assist us to distinguish arterial
strength from arterial debility, since in inflammatory diseases with
strength the frequency seldom exceeds one hundred and eighteen or one
hundred and twenty pulsations in a minute; unless under peculiar
circumstance, as the great additional stimuli of wine or of external
heat.

5. After a muscle or organ of sense has
been excited into contraction, and the sensorial power ceases to act, the
last situation or configuration of it continues; unless it be disturbed
by the action of some antagonist fibres, or other extraneous power. Thus
in weak or languid people, wherever they throw their limbs on their bed
or sofa, there they lie, till another exertion changes their attitude;
hence one kind of ocular spectra seems to be produced after looking at
bright objects; thus when a fire-stick is whirled round in the night,
there appears in the eye a complete circle of fire; the action or
configuration of one part of the retina not ceasing before the return of
the whirling fire.

Thus if any one looks at the setting sun for a short time, and then
covers his closed eyes with his hand, he will for many seconds of time
perceive the image of the sun on his retina. A similar image of all other
bodies would remain some time in the eye, but is effaced by the eternal
change of the motions of the extremity of this nerve in our attention to
other objects. See Sect. XVIII. 5. on Sleep.
Hence the dark spots, and other ocular spectra, are more frequently
attended to, and remain longer in the eyes of weak people, as after
violent exercise, intoxication, or want of sleep.

6. A contraction of the fibres somewhat
greater than usual introduces pleasurable sensation into the system,
according to the fourth law of animal causation. Hence the pleasure in
the beginning of drunkenness is owing to the increased action of the
system from the stimulus of vinous spirit or of opium. If the
contractions be still greater in energy or duration, painful sensations
are introduced, as in consequence of great heat, or caustic applications,
or fatigue.

If any part of the system, which is used to perpetual activity, as the
stomach, or heart, or the fine vessels of the skin, acts for a time with
less energy, another kind of painful sensation ensues, which is called
hunger, or faintness, or cold. This occurs in a less degree in the
locomotive muscles, and is called wearysomeness. In the two former kinds
of sensation there is an expenditure of sensorial power, in these latter
there is an accumulation of it.

7. We have used the words exertion of
sensorial power as a general term to express either irritation,
sensation, volition, or association; that is, to express the activity or
motion of the spirit of animation, at the time it produces the
contractions of the fibrous parts of the system. It may be supposed that
there may exist a greater or less mobility of the fibrous parts of our
system, or a propensity to be stimulated into contraction by the greater
or less quantity or energy of the spirit of animation; and that hence if
the exertion of the sensorial power be in its natural state, and the
mobility of the fibres be increased, the same quantity of fibrous
contraction will be caused, as if the mobility of the fibres continues in
its natural state, and the sensorial exertion be increased.

Thus it may be conceived, that in diseases accompanied with strength,
as in inflammatory fevers with arterial strength, that the cause of
greater fibrous contraction, may exist in the increased mobility of the
fibres, whose contractions are thence both more forceable and more
frequent. And that in diseases attended with debility, as in nervous
fevers, where the fibrous contractions are weaker, and more frequent, it
may be conceived that the cause consists in a decrease of mobility of the
fibres; and that those weak constitutions, which are attended with cold
extremities and large pupils of the eyes, may possess less mobility of
the contractile fibres, as well as less quantity of exertion of the
spirit of animation.

In answer to this mode of reasoning it may be sufficient to observe,
that the contractile fibres consist of inert matter, and when the
sensorial power is withdrawn, as in death, they possess no power of
motion at all, but remain in their last state, whether of contraction or
relaxation, and must thence derive the whole of this property from the
spirit of animation. At the same time it is not improbable, that the
moving fibres of strong people may possess a capability of receiving or
containing a greater quantity of the spirit of animation than those of
weak people.

In every contraction of a fibre there is an expenditure of the
sensorial power, or spirit of animation; and where the exertion of this
sensorial power has been for some time increased, and the muscles or
organs of sense have in consequence acted with greater energy, its
propensity to activity is proportionally lessened; which is to be
ascribed to the exhaustion or diminution of its quantity. On the
contrary, where there has been less fibrous contraction than usual for a
certain time, the sensorial power or spirit of animation becomes
accumulated in the inactive part of the system. Hence vigour succeeds
rest, and hence the propensity to action of all our organs of sense and
muscles is in a state of perpetual fluctuation. The irritability for
instance of the retina, that is, its quantity of sensorial power, varies
every moment according to the brightness or obscurity of the object last
beheld compared with the present one. The same occurs to our sense of
heat, and to every part of our system, which is capable of being excited
into action.

When this variation of the exertion of the sensorial power becomes
much and permanently above or beneath the natural quantity, it becomes a
disease. If the irritative motions be too great or too little, it shews
that the stimulus of external things affect this sensorial power too
violently or too inertly. If the sensitive motions be too great or too
little, the cause arises from the deficient or exuberant quantity of
sensation produced in consequence of the motions of the muscular fibres
or organs of sense; if the voluntary actions are diseased the cause is to
be looked for in the quantity of volition produced in consequence of the
desire or aversion occasioned by the painful or pleasurable sensations
above mentioned. And the diseases of associations probably depend on the
greater or less quantity of the other three sensorial powers by which
they were formed.

From whence it appears that the propensity to action, whether it be
called irritability, sensibility, voluntarity, or associability, is only
another mode of expression for the quantity of sensorial power residing
in the organ to be excited. And that on the contrary the words
inirritability and insensibility, together with inaptitude to voluntary
and associate motions, are synonymous with deficiency of the quantity of
sensorial power, or of the spirit of animation, residing in the organs to
be excited.

II. Of sensorial Exertion.

1. There are three circumstances to be
attended to in the production of animal motions, 1st. The stimulus. 2d.
The sensorial power. 3d. The contractile fibre. 1st. A stimulus, external
to the organ, originally induces into action the sensorial faculty termed
irritation; this produces the contraction of the fibres, which, if it be
perceived at all, introduces pleasure or pain; which in their active
state are termed sensation; which is another sensorial faculty, and
occasionally produces contraction of the fibres; this pleasure or pain is
therefore to be considered as another stimulus, which may either act
alone or in conjunction with the former faculty of the sensorium termed
irritation.

This new stimulus of pleasure or pain either induces into action the
sensorial faculty termed sensation, which then produces the contraction
of the fibres; or it introduces desire or aversion, which excite into
action another sensorial faculty, termed volition, and may therefore be
considered as another stimulus, which either alone or in conjunction with
one or both of the two former faculties of the sensorium produces the
contraction of animal fibres. There is another sensorial power, that of
association, which perpetually, in conjunction with one or more of the
above, and frequently singly, produces the contraction of animal fibres,
and which is itself excited into action by the previous motions of
contracting fibres.

Now as the sensorial power, termed irritation, residing in any
particular fibres, is excited into exertion by the stimulus of external
bodies acting on those fibres; the sensorial power, termed sensation,
residing in any particular fibres is excited into exertion by the
stimulus of pleasure or pain acting on those fibres; the sensorial power,
termed volition, residing in any particular fibres is excited into
exertion by the stimulus of desire or aversion; and the sensorial power,
termed association, residing in any particular fibres, is excited into
action by the stimulus of other fibrous motions, which had frequently
preceded them. The word stimulus may therefore be used without
impropriety of language, for any of these four causes, which excite the
four sensorial powers into exertion. For though the immediate cause of
volition has generally been termed a motive; and that of
irritation only has generally obtained the name of stimulus; yet
as the immediate cause, which excites the sensorial powers of sensation,
or of association into exertion, have obtained no general name, we shall
use the word stimulus for them all.

Hence the quantity of motion produced in any particular part of the
animal system will be as the quantity of stimulus and the quantity of
sensorial power, or spirit of animation, residing in the contracting
fibres. Where both these quantities are great, strength is
produced, when that word is applied to the motions of animal bodies.
Where either of them is deficient, weakness is produced, as
applied to the motions of animal bodies.

Now as the sensorial power, or spirit of animation, is perpetually
exhausted by the expenditure of it in fibrous contractions, and is
perpetually renewed by the secretion or production of it in the brain and
spinal marrow, the quantity of animal strength must be in a perpetual
state of fluctuation on this account; and if to this be added the
unceasing variation of all the four kinds of stimulus above described,
which produce the exertions of the sensorial powers, the ceaseless
vicissitude of animal strength becomes easily comprehended.

If the quantity of sensorial power remains the same, and the quantity
of stimulus be lessened, a weakness of the fibrous contractions ensues,
which may be denominated debility from defect of stimulus. If the
quantity of stimulus remains the same, and the quantity of sensorial
power be lessened, another kind of weakness ensues, which may be termed
debility from defect of sensorial power; the former of these is
called by Dr. Brown, in his Elements of Medicine, direct debility, and
the latter indirect debility. The coincidence of some parts of this work
with correspondent deductions in the Brunonian Elementa Medicina, a work
(with some exceptions) of great genius, must be considered as
confirmations of the truth of the theory, as they were probably arrived
at by different trains of reasoning.

Thus in those who have been exposed to cold and hunger there is a
deficiency of stimulus. While in nervous fever there is a deficiency of
sensorial power. And in habitual drunkards, in a morning before their
usual potation, there is a deficiency both of stimulus and of sensorial
power. While, on the other hand, in the beginning of intoxication there
is an excess of stimulus; in the hot-ach, after the hands have been
immersed in snow, there is a redundancy of sensorial power; and in
inflammatory diseases with arterial strength, there is an excess of
both.

Hence if the sensorial power be lessened, while the quantity of
stimulus remains the same as in nervous fever, the frequency of
repetition of the arterial contractions may continue, but their force in
respect to removing obstacles, as in promoting the circulation of the
blood, or the velocity of each contraction, will be diminished, that is,
the animal strength will be lessened. And secondly, if the quantity of
sensorial power be lessened, and the stimulus be increased to a certain
degree, as in giving opium in nervous fevers, the arterial contractions
may be performed more frequently than natural, yet with less
strength.

And thirdly, if the sensorial power continues the same in respect to
quantity, and the stimulus be somewhat diminished, as in going into a
darkish room, or into a coldish bath, suppose of about eighty degrees of
heat, as Buxton-bath, a temporary weakness of the affected fibres is
induced, till an accumulation of sensorial power gradually succeeds, and
counterbalances the deficiency of stimulus, and then the bath ceases to
feel cold, and the room ceases to appear dark; because the fibres of the
subcutaneous vessels, or of the organs of sense, act with their usual
energy.

A set of muscular fibres may thus be stimulated into violent exertion,
that is, they may act frequently, and with their whole sensorial power,
but may nevertheless not act strongly; because the quantity of their
sensorial power was originally small, or was previously exhausted. Hence
a stimulus may be great, and the irritation in consequence act with its
full force, as in the hot paroxysms of nervous fever; but if the
sensorial power, termed irritation, be small in quantity, the force of
the fibrous contractions, and the times of their continuance in their
contracted state, will be proportionally small.

In the same manner in the hot paroxysm of putrid fevers, which are
shewn in Sect. XXXIII. to be inflammatory
fevers with arterial debility, the sensorial power termed sensation is
exerted with great activity, yet the fibrous contractions, which produce
the circulation of the blood, are performed without strength, because the
quantity of sensorial power then residing in that part of the system is
small.

Thus in irritative fever with arterial strength, that is, with excess
of spirit of animation, the quantity of exertion during the hot part of
the paroxysm is to be estimated from the quantity of stimulus, and the
quantity of sensorial power. While in sensitive (or inflammatory) fever
with arterial strength, that is, with excess of spirit of animation, the
violent and forcible actions of the vascular system during the hot part
of the paroxysm are induced by the exertions of two sensorial powers,
which are excited by two kinds of stimulus. These are the sensorial power
of irritation excited by the stimulus of bodies external to the moving
fibres, and the sensorial power of sensation excited by the pain in
consequence of the increased contractions of those moving fibres.

And in insane people in some cases the force of their muscular actions
will be in proportion to the quantity of sensorial power, which they
possess, and the quantity of the stimulus of desire or aversion, which
excites their volition into action. At the same time in other cases the
stimulus of pain or pleasure, and the stimulus of external bodies, may
excite into action the sensorial powers of sensation and irritation, and
thus add greater force to their muscular actions.

2. The application of the stimulus, whether
that stimulus be some quality of external bodies, or pleasure or pain, or
desire or aversion, or a link of association, excites the correspondent
sensorial power into action, and this causes the contraction of the
fibre. On the contraction of the fibre a part of the spirit of animation
becomes expended, and the fibre ceases to contract, though the stimulus
continues to be applied; till in a certain time the fibre having received
a supply of sensorial power is ready to contract again, if the stimulus
continues to be applied. If the stimulus on the contrary be withdrawn,
the same quantity of quiescent sensorial power becomes resident in the
fibre as before its contraction; as appears from the readiness for action
of the large locomotive muscles of the body in a short time after common
exertion.

But in those muscular fibres, which are subject to constant stimulus,
as the arteries, glands, and capillary vessels, another phenomenon
occurs, if their accustomed stimulus be withdrawn; which is, that the
sensorial power becomes accumulated in the contractile fibres, owing to
the want of its being perpetually expended, or carried away, by their
usual unremitted contractions. And on this account those muscular fibres
become afterwards excitable into their natural actions by a much weaker
stimulus; or into unnatural violence of action by their accustomed
stimulus, as is seen in the hot fits of intermittent fevers, which are in
consequence of the previous cold ones. Thus the minute vessels of the
skin are constantly stimulated by the fluid matter of heat; if the
quantity of this stimulus of heat be a while diminished, as in covering
the hands with snow, the vessels cease to act, as appears from the
paleness of the skin; if this cold application of snow be continued but a
short time, the sensorial power, which had habitually been supplied to
the fibres, becomes now accumulated in them, owing to the want of its
being expended by their accustomed contractions. And thence a less
stimulus of heat will now excite them into violent contractions.

If the quiescence of fibres, which had previously been subject to
perpetual stimulus, continues a longer time; or their accustomed stimulus
be more completely withdrawn; the accumulation of sensorial power becomes
still greater, as in those exposed to cold and hunger; pain is produced,
and the organ gradually dies from the chemical changes, which take place
in it; or it is at a great distance of time restored to action by
stimulus applied with great caution in small quantity, as happens to some
larger animals and to many insects, which during the winter months lie
benumbed with cold, and are said to sleep, and to persons apparently
drowned, or apparently frozen to death. Snails have been said to revive
by throwing them into water after having been many years shut up in the
cabinets of the curious; and eggs and seeds in general are restored to
life after many months of torpor by the stimulus of warmth and
moisture.

The inflammation of schirrous tumours, which have long existed in a
state of inaction, is a process of this kind; as well as the sensibility
acquired by inflamed tendons and bones, which had at their formation a
similar sensibility, which had so long lain dormant in their uninflamed
state.

3. If after long quiescence from defect of
stimulus the fibres, which had previously been habituated to perpetual
stimulus, are again exposed to but their usual quantity of it; as in
those who have suffered the extremes of cold or hunger; a violent
exertion of the affected organ commences, owing, as above explained, to
the great accumulation of sensorial power. This violent exertion not only
diminishes the accumulated spirit of animation, but at the same time
induces pleasure or pain into the system, which, whether it be succeeded
by inflammation or not, becomes an additional stimulus, and acting along
with the former one, produces still greater exertions; and thus reduces
the sensorial power in the contracting fibres beneath its natural
quantity.

When the spirit of animation is thus exhausted by useless exertions,
the organ becomes torpid or unexcitable into action, and a second fit of
quiescence succeeds that of abundant activity. During this second fit of
quiescence the sensorial power becomes again accumulated, and another fit
of exertion follows in train. These vicissitudes of exertion and inertion
of the arterial system constitute the paroxysms of remittent fevers; or
intermittent ones, when there is an interval of the natural action of the
arteries between the exacerbations.

In these paroxysms of fevers, which consist of the libration of the
arterial system between the extremes of exertion and quiescence, either
the fits become less and less violent from the contractile fibres
becoming coming less excitable to the stimulus by habit, that is, by
becoming accustomed to it, as explained below XII. 3. 1. or the whole sensorial power becomes
exhausted, and the arteries cease to beat, and the patient dies in the
cold part of the paroxysm. Or secondly, so much pain is introduced into
the system by the violent contractions of the fibres, that inflammation
arises, which prevents future cold fits by expending a part of the
sensorial power in the extension of old vessels or the production of new
ones; and thus preventing the too great accumulation or exertion of it in
other parts of the system; or which by the great increase of stimulus
excites into great action the whole glandular system as well as the
arterial, and thence a greater quantity of sensorial power is produced in
the brain, and thus its exhaustion in any peculiar part of the system
ceases to be affected.

4. Or thirdly, in consequence of the
painful or pleasurable sensation above mentioned, desire and aversion are
introduced, and inordinate volition succeeds; which by its own exertions
expends so much of the spirit of animation, that the two other sensorial
faculties, or irritation and sensation, act so much more feebly; that the
paroxysms of fever, or that libration between the extremes of exertion
and inactivity of the arterial system, gradually subsides. On this
account a temporary insanity is a favourable sign in fevers, as I have
had some opportunities of observing.

III. Of repeated Stimulus.

1. When a stimulus is repeated more
frequently than the expenditure of sensorial power can be renewed in the
acting organ, the effect of the stimulus becomes gradually diminished.
Thus if two grains of opium be swallowed by a person unused to so strong
a stimulus, all the vascular systems in the body act with greater energy,
all the secretions and the absorption from those secreted fluids are
increased in quantity; and pleasure or pain are introduced into the
system, which adds an additional stimulus to that already too great.
After some hours the sensorial power becomes diminished in quantity,
expended by the great activity of the system; and thence, when the
stimulus of the opium is withdrawn, the fibres will not obey their usual
degree of natural stimulus, and a consequent torpor or quiescence
succeeds, as is experienced by drunkards, who on the day after a great
excess of spirituous potation feel indigestion, head-ach, and general
debility.

In this fit of torpor or quiescence of a part or of the whole of the
system, an accumulation of the sensorial power in the affected fibres is
formed, and occasions a second paroxysm of exertion by the application
only of the natural stimulus, and thus a libration of the sensorial
exertion between one excess and the other continues for two or three
days, where the stimulus was violent in degree; and for weeks in some
fevers, from the stimulus of contagious matter.

But if a second dose of opium be exhibited before the fibres have
regained their natural quantity of sensorial power, its effect will be
much less than the former, because the spirit of animation or sensorial
power is in part exhausted by the previous excess of exertion. Hence all
medicines repeated too frequently gradually lose their effect, as opium
and wine. Many things of disagreeable taste at first cease to be
disagreeable by frequent repetition, as tobacco; grief and pain gradually
diminish, and at length cease altogether, and hence life itself becomes
tolerable.

Besides the temporary diminution of the spirit of animation or
sensorial power, which is naturally stationary or resident in every
living fibre, by a single exhibition of a powerful stimulus, the
contractile fibres themselves, by the perpetual application of a new
quantity of stimulus, before they have regained their natural quantity of
sensorial power, appear to suffer in their capability of receiving so
much as the natural quantity of sensorial power; and hence a permanent
deficiency of spirit of animation takes place, however long the stimulus
may have been withdrawn. On this cause depends the permanent debility of
those, who have been addicted to intoxication, the general weakness of
old age, and the natural debility or inirritability of those, who have
pale skins and large pupils of their eyes.

There is a curious phenomenon belongs to this place, which has always
appeared difficult of solution; and that is, that opium or aloes may be
exhibited in small doses at first, and gradually increased to very large
ones without producing stupor or diarrhœa. In this case, though the
opium and aloes are given in such small doses as not to produce
intoxication or catharsis, yet they are exhibited in quantities
sufficient in some degree to exhaust the sensorial power, and hence a
stronger and a stronger dose is required; otherwise the medicine would
soon cease to act at all.

On the contrary, if the opium or aloes be exhibited in a large dose at
first, so as to produce intoxication or diarrhœa; after a few
repetitions the quantity of either of them may be diminished, and they
will still produce this effect. For the more powerful stimulus dissevers
the progressive catenations of animal motions, described in Sect. XVII. and introduces a new link between them;
whence every repetition strengthens this new association or catenation,
and the stimulus may be gradually decreased, or be nearly withdrawn, and
yet the effect shall continue; because the sensorial power of association
or catenation being united with the stimulus, increases in energy with
every repetition of the catenated circle; and it is by these means that
all the irritative associations of motions are originally produced.

2. When a stimulus is repeated at such
distant intervals of time, that the natural quantity of sensorial power
becomes completely restored in the acting fibres, it will act with the
same energy as when first applied. Hence those who have lately accustomed
themselves to large doses of opium by beginning with small ones, and
gradually increasing them, and repeating them frequently, as mentioned in
the preceding paragraph; if they intermit the use of it for a few days
only, must begin again with as small doses as they took at first,
otherwise they will experience the inconveniences of intoxication.

On this circumstance depend the constant unfailing effects of the
various kinds of stimulus, which excite into action all the vascular
systems in the body; the arterial, venous, absorbent, and glandular
vessels, are brought into perpetual unwearied action by the fluids, which
are adapted to stimulate them; but these have the sensorial power of
association added to that of irritation, and even in some degree that of
sensation, and even of volition, as will be spoken of in their places;
and life itself is thus carried on by the production of sensorial power
being equal to its waste or expenditure in the perpetual movement of the
vascular organization.

3. When a stimulus is repeated at uniform
intervals of time with such distances between them, that the expenditure
of sensorial power in the acting fibres becomes completely renewed, the
effect is produced with greater facility or energy. For the sensorial
power of association is combined with the sensorial power of irritation,
or, in common language, the acquired habit assists the power of the
stimulus.

This circumstance not only obtains in the annual and diurnal
catenations of animal motions explained in Sect. XXXVI. but in every less circle of actions or
ideas, as in the burthen of a song, or the iterations of a dance; and
constitutes the pleasure we receive from repetition and imitation; as
treated of in Sect. XXII. 2.

4. When a stimulus has been many times
repeated at uniform intervals, so as to produce the complete action of
the organ, it may then be gradually diminished, or totally withdrawn, and
the action of the organ will continue. For the sensorial power of
association becomes united with that of irritation, and by frequent
repetition becomes at length of sufficient energy to carry on the new
link in the circle of actions, without the irritation which at first
introduced it.

Hence, when the bark is given at stated intervals for the cure of
intermittent fevers, if sixty grains of it be given every three hours for
the twenty-four hours preceding the expected paroxysm, so as to stimulate
the defective part of the system into action, and by that means to
prevent the torpor or quiescence of the fibres, which constitutes the
cold fit; much less than half the quantity, given before the time at
which another paroxysm of quiescence would have taken place, will be
sufficient to prevent it; because now the sensorial power, termed
association, acts in a twofold manner. First, in respect to the period of
the catenation in which the cold fit was produced, which is now
dissevered by the stronger stimulus of the first doses of the bark; and,
secondly, because each dose of bark being repeated at periodical times,
has its effect increased by the sensorial faculty of association being
combined with that of irritation.

Now, when sixty grains of Peruvian bark are taken twice a day, suppose
at ten o’clock and at six, for a fortnight, the irritation excited by
this additional stimulus becomes a part of the diurnal circle of actions,
and will at length carry on the increased action of the system without
the assistance of the stimulus of the bark. On this theory the bitter
medicines, chalybeates, and opiates in appropriated doses, exhibited for
a fortnight, give permanent strength to pale feeble children, and other
weak constitutions.

5. When a defect of stimulus, as of heat,
recurs at certain diurnal intervals, which induces some torpor or
quiescence of a part of the system, the diurnal catenation of actions
becomes disordered, and a new association with this link of torpid action
is formed; on the next period the quantity of quiescence will be
increased, suppose the same defect of stimulus to recur, because now the
new association conspires with the defective irritation in introducing
the torpid action of this part of the diurnal catenation. In this manner
many fever-fits commence, where the patient is for some days indisposed
at certain hours, before the cold paroxysm of fever is completely formed.
See Sect. XVII. 3. 3. on Catenation of
Animal Motions.

6. If a stimulus, which at first excited
the affected organ into so great exertion as to produce sensation, be
continued for a certain time, it will cease to produce sensation both
then and when repeated, though the irritative motions in consequence of
it may continue or be re-excited.

Many catenations of irritative motions were at first succeeded by
sensation, as the apparent motions of objects when we walk past them, and
probably the vital motions themselves in the early state of our
existence. But as those sensations were followed by no movements of the
system in consequence of them, they gradually ceased to be produced, not
being joined to any succeeding link of catenation. Hence contagious
matter, which has for some weeks stimulated the system into great and
permanent sensation, ceases afterwards to produce general sensation, or
inflammation, though it may still induce topical irritations. See Sect.
XXXIII. 2. 8. XIX.
9.

Our absorbent system then seems to receive those contagious matters,
which it has before experienced, in the same manner as it imbibes common
moisture or other fluids; that is, without being thrown into so violent
action as to produce sensation; the consequence of which is an increase
of daily energy or activity, till inflammation and its consequences
succeed.

7. If a stimulus excites an organ into such
violent contractions as to produce sensation, the motions of which organ
had not usually produced sensation, this new sensorial power, added to
the irritation occasioned by the stimulus, increases the activity of the
organ. And if this activity be catenated with the diurnal circle of
actions, an increasing inflammation is produced; as in the evening
paroxysms of small-pox, and other fevers with inflammation. And hence
schirrous tumours, tendons and membranes, and probably the arteries
themselves become inflamed, when they are strongly stimulated.

IV. Of Stimulus greater than natural.

1. A quantity of stimulus greater than
natural, producing an increased exertion of sensorial power, whether that
exertion be in the mode of irritation, sensation, volition, or
association, diminishes the general quantity of it. This fact is
observable in the progress of intoxication, as the increased quantity or
energy of the irritative motions, owing to the stimulus of vinous spirit,
introduces much pleasurable sensation into the system, and much exertion
of muscular or sensual motions in consequence of this increased
sensation; the voluntary motions, and even the associate ones, become
much impaired or diminished; and delirium and staggering succeed. See
Sect. XXI. on Drunkenness. And hence the great
prostration of the strength of the locomotive muscles in some fevers, is
owing to the exhaustion of sensorial power by the increased action of the
arterial system.

In like manner a stimulus greater than natural, applied to a part of
the system, increases the exertion of sensorial power in that part, and
diminishes it in some other part. As in the commencement of scarlet
fever, it is usual to see great redness and heat on the faces and breasts
of children, while at the same time their feet are colder than natural;
partial heats are observable in other fevers with debility, and are
generally attended with torpor or quiescence of some other part of the
system. But these partial exertions of sensorial power are sometimes
attended with increased partial exertions in other parts of the system,
which sympathize with them, as the flushing of the face after a full
meal. Both these therefore are to be ascribed to sympathetic
associations, explained in Sect. XXXV. and not
to general exhaustion or accumulation of sensorial power.

2. A quantity of stimulus greater than
natural, producing an increased exertion of sensorial power in any
particular organ, diminishes the quantity of it in that organ. This
appears from the contractions of animal fibres being not so easily
excited by a less stimulus after the organ has been subjected to a
greater. Thus after looking at any luminous object of a small size, as at
the setting sun, for a short time, so as not much to fatigue the eye,
this part of the retina becomes less sensible to smaller quantities of
light; hence when the eyes are turned on other less luminous parts of the
sky, a dark spot is seen resembling the shape of the sun, or other
luminous object which we last behold. See Sect. XL.
No. 2.

Thus we are some time before we can distinguish objects in an obscure
room after coming from bright day-light, though the iris presently
contracts itself. We are not able to hear weak sounds after loud ones.
And the stomachs of those who have been much habituated to the stronger
stimulus of fermented or spirituous liquors, are not excited into due
action by weaker ones.

3. A quantity of stimulus something greater
than the last mentioned, or longer continued, induces the organ into
spasmodic action, which ceases and recurs alternately. Thus on looking
for a time on the setting sun, so as not greatly to fatigue the sight, a
yellow spectrum is seen when the eyes are closed and covered, which
continues for a time, and then disappears and recurs repeatedly before it
entirely vanishes. See Sect. XL. No. 5. Thus the
action of vomiting ceases and is renewed by intervals, although the
emetic drug is thrown up with the first effort. A tenesmus continues by
intervals some time after the exclusion of acrid excrement; and the
pulsations of the heart of a viper are said to continue some time after
it is cleared from its blood.

In these cases the violent contractions of the fibres produce pain
according to law 4; and this pain constitutes an additional kind or
quantity of excitement, which again induces the fibres into contraction,
and which painful excitement is again renewed, and again induces
contractions of the fibres with gradually diminishing effect.

4. A quantity of stimulus greater than that
last mentioned, or longer continued, induces the antagonist muscles into
spasmodic action. This is beautifully illustrated by the ocular spectra
described in Sect. XL. No. 6. to which the
reader is referred. From those experiments there is reason to conclude
that the fatigued part of the retina throws itself into a contrary mode
of action like oscitation or pandiculation, as soon as the stimulus,
which has fatigued it, is withdrawn; but that it still remains liable to
be excited into action by any other colours except the colour with which
it has been fatigued. Thus the yawning and stretching the limbs after a
continued action or attitude seems occasioned by the antagonist muscles
being stimulated by their extension during the contractions of those in
action, or in the situation in which that action last left them.

5. A quantity of stimulus greater than the
last, or longer continued, induces variety of convulsions or fixed spasms
either of the affected organ or of the moving fibres in the other parts
of the body. In respect to the spectra in the eye, this is well
illustrated in No. 7 and 8, of Sect. XL. Epileptic convulsions, as the
emprosthotonos and opisthotonos, with the cramp of the calf of the leg,
locked jaw, and other cataleptic fits, appear to originate from pain, as
some of these patients scream aloud before the convulsion takes place;
which seems at first to be an effort to relieve painful sensation, and
afterwards an effort to prevent it.

In these cases the violent contractions of the fibres produce so much
pain, as to constitute a perpetual excitement; and that in so great a
degree as to allow but small intervals of relaxation of the contracting
fibres as in convulsions, or no intervals at all as in fixed spasms.

6. A quantity of stimulus greater than the
last, or longer continued, produces a paralysis of the organ. In many
cases this paralysis is only a temporary effect, as on looking long on a
small area of bright red silk placed on a sheet of white paper on the
floor in a strong light, the red silk gradually becomes paler, and at
length disappears; which evinces that a part of the retina, by being
violently excited, becomes for a time unaffected by the stimulus of that
colour. Thus cathartic medicines, opiates, poisons, contagious matter,
cease to influence our system after it has been habituated to the use of
them, except by the exhibition of increased quantities of them; our
fibres not only become unaffected by stimuli, by which they have
previously been violently irritated, as by the matter of the small-pox or
measles; but they also become unaffected by sensation, where the violent
exertions, which disabled them, were in consequence of too great quantity
of sensation. And lastly the fibres, which become disobedient to
volition, are probably disabled by their too violent exertions in
consequence of too great a quantity of volition.

After every exertion of our fibres a temporary paralysis succeeds,
whence the intervals of all muscular contractions, as mentioned in No. 3
and 4 of this Section; the immediate cause of these more permanent kinds
of paralysis is probably owing in the same manner to the too great
exhaustion of the spirit of animation in the affected part; so that a
stronger stimulus is required, or one of a different kind from that,
which occasioned those too violent contractions, to again excite the
affected organ into activity; and if a stronger stimulus could be
applied, it must again induce paralysis.

For these powerful stimuli excite pain at the same time, that they
produce irritation; and this pain not only excites fibrous motions by its
stimulus, but it also produces volition; and thus all these stimuli
acting at the same time, and sometimes with the addition of their
associations, produce so great exertion as to expend the whole of the
sensorial power in the affected fibres.

V. Of Stimulus less than natural.

1. A quantity of stimulus less than
natural, producing a decreased exertion of sensorial power, occasions an
accumulation of the general quantity of it. This circumstance is
observable in the hemiplagia, in which the patients are perpetually
moving the muscles, which are unaffected. On this account we awake with
greater vigour after sleep, because during so many hours, the great usual
expenditure of sensorial power in the performance of voluntary actions,
and in the exertions of our organs of sense, in consequence of the
irritations occasioned by external objects had been suspended, and a
consequent accumulation had taken place.

In like manner the exertion of the sensorial power less than natural
in one part of the system, is liable to produce an increase of the
exertion of it in some other part. Thus by the action of vomiting, in
which the natural exertion of the motions of the stomach are destroyed or
diminished, an increased absorption of the pulmonary and cellular
lymphatics is produced, as is known by the increased absorption of the
fluid deposited in them in dropsical cases. But these partial quiescences
of sensorial power are also sometimes attended with other partial
quiescences, which sympathize with them, as cold and pale extremities
from hunger. These therefore are to be ascribed to the associations of
sympathy explained in Sect. XXXV. and not to the
general accumulation of sensorial power.

2. A quantity of stimulus less than
natural, applied to fibres previously accustomed to perpetual stimulus,
is succeeded by accumulation of sensorial power in the affected organ.
The truth of this proposition is evinced, because a stimulus less than
natural, if it be somewhat greater than that above mentioned, will excite
the organ so circumstanced into violent activity. Thus on a frosty day
with wind, the face of a person exposed to the wind is at first pale and
shrunk; but on turning the face from the wind, it becomes soon of a glow
with warmth and flushing. The glow of the skin in emerging from the
cold-bath is owing to the same cause.

It does not appear, that an accumulation of sensorial power above the
natural quantity is acquired by those muscles, which are not subject to
perpetual stimulus, as the locomotive muscles: these, after the greatest
fatigue, only acquire by rest their usual aptitude to motion; whereas the
vascular system, as the heart and arteries, after a short quiescence, are
thrown into violent action by their natural quantity of stimulus.

Nevertheless by this accumulation of sensorial power during the
application of decreased stimulus, and by the exhaustion of it during the
action of increased stimulus, it is wisely provided, that the actions of
the vascular muscles and organs of sense are not much deranged by small
variations of stimulus; as the quantity of sensorial power becomes in
some measure inversely as the quantity of stimulus.

3. A quantity of stimulus less than that
mentioned above, and continued for some time, induces pain in the
affected organ, as the pain of cold in the hands, when they are immersed
in snow, is owing to a deficiency of the stimulation of heat. Hunger is a
pain from the deficiency of the stimulation of food. Pain in the back at
the commencement of ague-fits, and the head-achs which attend feeble
people, are pains from defect of stimulus, and are hence relieved by
opium, essential oils, spirit of wine.

As the pains, which originate from defect of stimulus, only occur in
those parts of the system, which have been previously subjected to
perpetual stimulus; and as an accumulation of sensorial power is produced
in the quiescent organ along with the pain, as in cold or hunger, there
is reason to believe, that the pain is owing to the accumulation of
sensorial power. For, in the locomotive muscles, in the retina of the
eye, and other organs of senses, no pain occurs from the absence of
stimulus, nor any great accumulation of sensorial power beyond their
natural quantity, since these organs have not been used to a perpetual
supply of it. There is indeed a greater accumulation occurs in the organ
of vision after its quiescence, because it is subject to more constant
stimulus.

4. A certain quantity of stimulus less than
natural induces the moving organ into feebler and more frequent
contractions, as mentioned in No. I. 4. of
this Section. For each contraction moving through a less space, or with
less force, that is, with less expenditure of the spirit of animation, is
sooner relaxed, and the spirit of animation derived at each interval into
the acting fibres being less, these intervals likewise become shorter.
Hence the tremours of the hands of people accustomed to vinous spirit,
till they take their usual stimulus; hence the quick pulse in fevers
attended with debility, which is greater than in fevers attended with
strength; in the latter the pulse seldom beats above 120 times in a
minute, in the former it frequently exceeds 140.

It must be observed, that in this and the two following articles the
decreased action of the system is probably more frequently occasioned by
deficiency in the quantity of sensorial power, than in the quantity of
stimulus. Thus those feeble constitutions which have large pupils of
their eyes, and all who labour under nervous fevers, seem to owe their
want of natural quantity of activity in the system to the deficiency of
sensorial power; since, as far as can be seen, they frequently possess
the natural quantity of stimulus.

5. A certain quantity of stimulus, less
than that above mentioned, inverts the order of successive fibrous
contractions; as in vomiting the vermicular motions of the stomach and
duodenum are inverted, and their contents ejected, which is probably
owing to the exhaustion of the spirit of animation in the acting muscles
by a previous excessive stimulus, as by the root of ipecacuanha, and the
consequent defect of sensorial power. The same retrograde motions affect
the whole intestinal canal in ileus; and the œsophagus in globus
hystericus. See this further explained in Sect. XXIX. No. 11. on Retrograde Motions.

I must observe, also, that something similar happens in the production
of our ideas, or sensual motions, when they are too weakly excited; when
any one is thinking intensely about one thing, and carelessly conversing
about another, he is liable to use the word of a contrary meaning to that
which he designed, as cold weather for hot weather, summer for
winter.

6. A certain quantity of stimulus, less
than that above mentioned, is succeeded by paralysis, first of the
voluntary and sensitive motions, and afterwards of those of irritation,
and of association, which constitutes death.

VI. Cure of increased Exertion.

1. The cure, which nature has provided for
the increased exertion of any part of the system, consists in the
consequent expenditure of the sensorial power. But as a greater torpor
follows this exhaustion of sensorial power, as explained in the next
paragraph, and a greater exertion succeeds this torpor, the constitution
frequently sinks under these increasing librations between exertion and
quiescence; till at length complete quiescence, that is, death, closes
the scene.

For, during the great exertion of the system in the hot fit of fever,
an increase of stimulus is produced from the greater momentum of the
blood, the greater distention of the heart and arteries, and the
increased production of heat, by the violent actions of the system
occasioned by this augmentation of stimulus, the sensorial power becomes
diminished in a few hours much beneath its natural quantity, the vessels
at length cease to obey even these great degrees of stimulus, as shewn in
Sect. XL. 9. 1. and a torpor of the whole or
of a part of the system ensues.

Now as this second cold fit commences with a greater deficiency of
sensorial power, it is also attended with a greater deficiency of
stimulus than in the preceding cold fit, that is, with less momentum of
blood, less distention of the heart. On this account the second cold fit
becomes more violent and of longer duration than the first; and as a
greater accumulation of sensorial power must be produced before the
system of vessels will again obey the diminished stimulus, it follows,
that the second hot fit of fever will be more violent than the former
one. And that unless some other causes counteract either the violent
exertions in the hot fit, or the great torpor in the cold fit, life will
at length be extinguished by the expenditure of the whole of the
sensorial power. And from hence it appears, that the true means of curing
fevers must be such as decrease the action of the system in the hot fit,
and increase it in the cold fit; that is, such as prevent the too great
diminution of sensorial power in the hot fit, and the too great
accumulation of it in the cold one.

2. Where the exertion of the sensorial
powers is much increased, as in the hot fits of fever or inflammation,
the following are the usual means of relieving it. Decrease the
irritations by blood-letting, and other evacuations; by cold water taken
into the stomach, or injected as an enema, or used externally; by cold
air breathed into the lungs, and diffused over the skin; with food of
less stimulus than the patient has been accustomed to.

3. As a cold fit, or paroxysm of inactivity
of some parts of the system, generally precedes the hot fit, or paroxysm
of exertion, by which the sensorial power becomes accumulated, this cold
paroxysm should be prevented by stimulant medicines and diet, as wine,
opium, bark, warmth, cheerfulness, anger, surprise.

4. Excite into greater action some other
part of the system, by which means the spirit of animation may be in part
expended, and thence the inordinate actions of the diseased part may be
lessened. Hence when a part of the skin acts violently, as of the face in
the eruption of the small-pox, if the feet be cold they should be
covered. Hence the use of a blister applied near a topical inflammation.
Hence opium and warm bath relieve pains both from excess and defect of
stimulus.

5. First increase the general stimulation
above its natural quantity, which may in some degree exhaust the spirit
of animation, and then decrease the stimulation beneath its natural
quantity. Hence after sudorific medicines and warm air, the application
of refrigerants may have greater effect, if they could be administered
without danger of producing too great torpor of some part of the system;
as frequently happens to people in health from coming out of a warm room
into the cold air, by which a topical inflammation in consequence of
torpor of the mucous membrane of the nostril is produced, and is termed a
cold in the head.

VII. Cure of decreased Exertion.

1. Where the exertion of the sensorial
powers is much decreased, as in the cold fits of fever, a gradual
accumulation of the spirit of animation takes place; as occurs in all
cases where inactivity or torpor of a part of the system exists; this
accumulation of sensorial power increases, till stimuli less than natural
are sufficient to throw it into action, then the cold fit ceases; and
from the action of the natural stimuli a hot one succeeds with increased
activity of the whole system.

So in fainting fits, or syncope, there is a temporary deficiency of
sensorial exertion, and a consequent quiescence of a great part of the
system. This quiescence continues, till the sensorial power becomes again
accumulated in the torpid organs; and then the usual diurnal stimuli
excite the revivescent parts again into action; but as this kind of
quiescence continues but a short time compared to the cold paroxysm of an
ague, and less affects the circulatory system, a less superabundancy of
exertion succeeds in the organs previously torpid, and a less excess of
arterial activity. See Sect. XXXIV. 1.
6.

2. In the diseases occasioned by a defect
of sensorial exertion, as in cold fits of ague, hysteric complaint, and
nervous fever, the following means are those commonly used. 1. Increase
the stimulation above its natural quantity for some weeks, till a new
habit of more energetic contraction of the fibres is established. This is
to be done by wine, opium, bark, steel, given at exact periods, and in
appropriate quantities; for if these medicines be given in such quantity,
as to induce the least degree of intoxication, a debility succeeds from
the useless exhaustion of spirit of animation in consequence of too great
exertion of the muscles or organs of sense. To these irritative stimuli
should be added the sensitive ones of cheerful ideas, hope,
affection.

3. Change the kinds of stimulus. The habits
acquired by the constitution depend on such nice circumstances, that when
one kind of stimulus ceases to excite the sensorial power into the
quantity of exertion necessary to health, it is often sufficient to
change the stimulus for another apparently similar in quantity and
quality. Thus when wine ceases to stimulate the constitution, opium in
appropriate doses supplies the defect; and the contrary. This is also
observed in the effects of cathartic medicines, when one loses its power,
another, apparently less efficacious, will succeed. Hence a change of
diet, drink, and stimulating medicines, is often advantageous in diseases
of debility.

4. Stimulate the organs, whose motions are
associated with the torpid parts of the system. The actions of the minute
vessels of the various parts of the external skin are not only associated
with each other, but are strongly associated with those of some of the
internal membranes, and particularly of the stomach. Hence when the
exertion of the stomach is less than natural, and indigestion and
heartburn succeed, nothing so certainly removes these symptoms as the
stimulus of a blister on the back. The coldness of the extremities, as of
the nose, ears, or fingers, are hence the best indication for the
successful application of blisters.

5. Decrease the stimulus for a time. By
lessening the quantity of heat for a minute or two by going into the cold
bath, a great accumulation of sensorial power is produced; for not only
the minute vessels of the whole external skin for a time become inactive,
as appears by their paleness; but the minute vessels of the lungs lose
much of their activity also by concert with those of the skin, as appears
from the difficulty of breathing at first going into cold water. On
emerging from the bath the sensorial power is thrown into great exertion
by the stimulus of the common degree of the warmth of the atmosphere, and
a great production of animal heat is the consequence. The longer a person
continues in the cold bath the greater must be the present inertion of a
great part of the system, and in consequence a greater accumulation of
sensorial power. Whence M. Pomè recommends some melancholy patients to be
kept from two to six hours in spring-water, and in baths still
colder.

6. Decrease the stimulus for a time below
the natural, and then increase it above natural. The effect of this
process, improperly used, is seen in giving much food, or applying much
warmth, to those who have been previously exposed to great hunger, or to
great cold. The accumulated sensorial power is thrown into so violent
exertion, that inflammations and mortifications supervene, and death
closes the catastrophe. In many diseases this method is the most
successful; hence the bark in agues produces more certain effect after
the previous exhibition of emetics. In diseases attended with violent
pain, opium has double the effect, if venesection and a cathartic have
been previously used. On this seems to have been founded the successful
practice of Sydenham, who used venesection and a cathartic in chlorosis
before the exhibition of the bark, steel, and opiates.

7. Prevent any unnecessary expenditure of
sensorial power. Hence in fevers with debility, a decumbent posture is
preferred, with silence, little light, and such a quantity of heat as may
prevent any chill sensation, or any coldness of the extremities. The
pulse of patients in fevers with debility increases in frequency above
ten pulsations in a minute on their rising out of bed. For the
expenditure of sensorial power to preserve an erect posture of the body
adds to the general deficiency of it, and thus affects the
circulation.

8. The longer in time and the greater in
degree the quiescence or inertion of an organ has been, so that it still
retains life or excitability, the less stimulus should at first be
applied to it. The quantity of stimulation is a matter of great nicety to
determine, where the torpor or quiescence of the fibres has been
experienced in a great degree, or for a considerable time, as in cold
fits of the ague, in continued fevers with great debility, or in people
famished at sea, or perishing with cold. In the two last cases, very
minute quantities of food should be first supplied, and very few
additional degrees of heat. In the two former cases, but little stimulus
of wine or medicine, above what they had been lately accustomed to,
should be exhibited, and this at frequent and stated intervals, so that
the effect of one quantity may be observed before the exhibition of
another.

If these circumstances are not attended to, as the sensorial power
becomes accumulated in the quiescent fibres, an inordinate exertion takes
place by the increase of stimulus acting on the accumulated quantity of
sensorial power, and either the paralysis, or death of the contractile
fibres ensues, from the total expenditure of the sensorial power in the
affected organ, owing to this increase of exertion, like the debility
after intoxication. Or, secondly, the violent exertions above mentioned
produce painful sensation, which becomes a new stimulus, and by thus
producing inflammation, and increasing the activity of the fibres already
too great, sooner exhausts the whole of the sensorial power in the acting
organ, and mortification, that is, the death of the part, supervenes.

Hence there have been many instances of people, whose limbs have been
long benumbed by exposure to cold, who have lost them by mortification on
their being too hastily brought to the fire; and of others, who were
nearly famished at sea, who have died soon after having taken not more
than an usual meal of food. I have heard of two well-attested instances
of patients in the cold fit of ague, who have died from the exhibition of
gin and vinegar, by the inflammation which ensued. And in many fevers
attended with debility, the unlimited use of wine, and the wanton
application of blisters, I believe, has destroyed numbers by the debility
consequent to too great stimulation, that is, by the exhaustion of the
sensorial power by its inordinate exertion.

Wherever the least degree of intoxication exists, a proportional
debility is the consequence; but there is a golden rule by which the
necessary and useful quantity of stimulus in fevers with debility may be
ascertained. When wine or beer are exhibited either alone or diluted with
water, if the pulse becomes slower the stimulus is of a proper quantity;
and should be repeated every two or three hours, or when the pulse again
becomes quicker.

In the chronical debility brought on by drinking spirituous or
fermented liquors, there is another golden rule by which I have
successfully directed the quantity of spirit which they may safely
lessen, for there is no other means by which they can recover their
health. It should be premised, that where the power of digestion in these
patients is totally destroyed, there is not much reason to expect a
return to healthful vigour.

I have directed several of these patients to omit one fourth part of
the quantity of vinous spirit they have been lately accustomed to, and if
in a fortnight their appetite increases, they are advised to omit another
fourth part; but if they perceive that their digestion becomes impaired
from the want of this quantity of spirituous potation, they are advised
to continue as they are, and rather bear the ills they have, than risk
the encounter of greater. At the same time flesh-meat with or without
spice is recommended, with Peruvian bark and steel in small quantities
between their meals, and half a grain of opium or a grain, with five or
eight grains of rhubarb at night.

SECT. XIII.

OF VEGETABLE ANIMATION.

I. 1.
Vegetables are irritable; mimosa, dionæa muscipula. Vegetable
secretions. 2. Vegetable buds are
inferior animals, are liable to greater or less irritability. II. Stamens and pistils of plants shew marks
of sensibility. III. Vegetables possess
some degree of volition. IV. Motions of
plants are associated like those of animals. V. 1. Vegetable
structure like that of animals, their anthers and stigmas are living
creatures. Male-flowers of Vallisneria. 2. Whether vegetables, possess ideas? They
have organs of sense as of touch and smell, and ideas of external
things?

I. 1. The fibres
of the vegetable world, as well as those of the animal, are excitable
into a variety of motion by irritations of external objects. This appears
particularly in the mimosa or sensitive plant, whose leaves contract on
the slightest injury; the dionæa muscipula, which was lately brought over
from the marshes of America, presents us with another curious instance of
vegetable irritability; its leaves are armed with spines on their upper
edge, and are spread on the ground around the stem; when an insect creeps
on any of them in its passage to the flower or seed, the leaf shuts up
like a steel rat-trap, and destroys its enemy. See Botanic Garden, Part
II. note on Silene.

The various secretions of vegetables, as of odour, fruit, gum, resin,
wax, honey, seem brought about in the same manner as in the glands of
animals; the tasteless moisture of the earth is converted by the
hop-plant into a bitter juice; as by the caterpillar in the nut-shell the
sweet kernel is converted into a bitter powder. While the power of
absorption in the roots and barks of vegetables is excited into action by
the fluids applied to their mouths like the lacteals and lymphatics of
animals.

2. The individuals of the vegetable world
may be considered as inferior or less perfect animals; a tree is a
congeries of many living buds, and in this respect resembles the branches
of coralline, which are a congeries of a multitude of animals. Each of
these buds of a tree has its proper leaves or petals for lungs, produces
its viviparous or its oviparous offspring in buds or seeds; has its own
roots, which extending down the stem of the tree are interwoven with the
roots of the other buds, and form the bark, which is the only living part
of the stem, is annually renewed, and is superinduced upon the former
bark, which then dies, and with its stagnated juices gradually hardening
into wood forms the concentric circles, which we see in blocks of
timber.

The following circumstances evince the individuality of the buds of
trees. First, there are many trees, whose whole internal wood is
perished, and yet the branches are vegete and healthy. Secondly, the
fibres of the barks of trees are chiefly longitudinal, resembling roots,
as is beautifully seen in those prepared barks, that were lately brought
from Otaheita. Thirdly, in horizontal wounds of the bark of trees, the
fibres of the upper lip are always elongated downwards like roots, but
those of the lower lip do not approach to meet them. Fourthly, if you
wrap wet moss round any joint of a vine, or cover it with moist earth,
roots will shoot out from it. Fifthly, by the inoculation or engrafting
of trees many fruits are produced from one stem. Sixthly, a new tree is
produced from a branch plucked from an old one, and set in the ground.
Whence it appears that the buds of deciduous trees are so many annual
plants, that the bark is a contexture of the roots of each individual
bud; and that the internal wood is of no other use but to support them in
the air, and that thus they resemble the animal world in their
individuality.

The irritability of plants, like that of animals, appears liable to be
increased or decreased by habit; for those trees or shrubs, which are
brought from a colder climate to a warmer, put out their leaves and
blossoms a fortnight sooner than the indigenous ones.

Professor Kalm, in his Travels in New York, observes that the
apple-trees brought from England blossom a fortnight sooner than the
native ones. In our country the shrubs, that are brought a degree or two
from the north, are observed to flourish better than those, which come
from the south. The Siberian barley and cabbage are said to grow larger
in this climate than the similar more southern vegetables. And our hoards
of roots, as of potatoes and onions, germinate with less heat in spring,
after they have been accustomed to the winter’s cold, than in autumn
after the summer’s heat.

II. The stamens and pistils of flowers shew
evident marks of sensibility, not only from many of the stamens and some
pistils approaching towards each other at the season of impregnation, but
from many of them closing their petals and calyxes during the cold parts
of the day. For this cannot be ascribed to irritation, because cold means
a defect of the stimulus of heat; but as the want of accustomed stimuli
produces pain, as in coldness, hunger, and thirst of animals, these
motions of vegetables in closing up their flowers must be ascribed to the
disgreeable sensation, and not to the irritation of cold. Others close up
their leaves during darkness, which, like the former, cannot be owing to
irritation, as the irritating material is withdrawn.

The approach of the anthers in many flowers to the stigmas, and of the
pistils of some flowers to the anthers, must be ascribed to the passion
of love, and hence belongs to sensation, not to irritation.

III. That the vegetable world possesses some
degree of voluntary powers, appears from their necessity to sleep, which
we have shewn in Sect. XVIII. to consist in the
temporary abolition of voluntary power. This voluntary power seems to be
exerted in the circular movement of the tendrils of vines, and other
climbing vegetables; or in the efforts to turn the upper surface of their
leaves, or their flowers to the light.

IV. The associations of fibrous motions are
observable in the vegetable world, as well as in the animal. The
divisions of the leaves of the sensitive plant have been accustomed to
contract at the same time from the absence of light; hence if by any
other circumstance, as a slight stroke or injury, one division is
irritated into contraction, the neighbouring ones contract also, from
their motions being associated with those of the irritated part. So the
various stamina of the class of syngenesia have been accustomed to
contract together in the evening, and thence if you stimulate one of them
with a pin, according to the experiment of M. Colvolo, they all contract
from their acquired associations.

To evince that the collapsing of the sensitive plant is not owing to
any mechanical vibrations propagated along the whole branch, when a
single leaf is struck with the finger, a leaf of it was slit with sharp
scissors, and some seconds of time passed before the plant seemed
sensible of the injury; and then the whole branch collapsed as far as the
principal stem: this experiment was repeated several times with the least
possible impulse to the plant.

V. 1. For the
numerous circumstances in which vegetable buds are analogous to animals,
the reader is referred to the additional notes at the end of the Botanic
Garden, Part I. It is there shewn, that the roots of vegetables resemble
the lacteal system of animals; the sap-vessels in the early spring,
before their leaves expand, are analogous to the placental vessels of the
fœtus; that the leaves of land-plants resemble lungs, and those of
aquatic plants the gills of fish; that there are other systems of vessels
resembling the vena portarum of quadrupeds, or the aorta of fish; that
the digestive power of vegetables is similar to that of animals
converting the fluids, which they absorb, into sugar; that their seeds
resemble the eggs of animals, and their buds and bulbs their viviparous
offspring. And, lastly, that the anthers and stigmas are real animals,
attached indeed to their parent tree like polypi or coral insects, but
capable of spontaneous motion; that they are affected with the passion of
love, and furnished with powers of reproducing their species, and are fed
with honey like the moths and butterflies, which plunder their nectaries.
See Botanic Garden, Part I. add. note XXXIX.

The male flowers of vallisneria approach still nearer to apparent
animality, as they detach themselves from the parent plant, and float on
the surface of the water to the female ones. Botanic Garden, Part II.
Art. Vallisneria. Other flowers of the classes of monecia and diecia, and
polygamia, discharge the fecundating farina, which floating in the air is
carried to the stigma of the female flowers, and that at considerable
distances. Can this be effected by any specific attraction? or, like the
diffusion of the odorous particles of flowers, is it left to the currents
of winds, and the accidental miscarriages of it counteracted by the
quantity of its production?

2. This leads us to a curious enquiry,
whether vegetables have ideas of external things? As all our ideas are
originally received by our senses, the question may be changed to,
whether vegetables possess any organs of sense? Certain it is, that they
possess a sense of heat and cold, another of moisture and dryness, and
another of light and darkness; for they close their petals occasionally
from the presence of cold, moisture, or darkness. And it has been already
shewn, that these actions cannot be performed simply from irritation,
because cold and darkness are negative quantities, and on that account
sensation or volition are implied, and in consequence a sensorium or
union of their nerves. So when we go into the light, we contract the
iris; not from any stimulus of the light on the fine muscles of the iris,
but from its motions being associated with the sensation of too much
light on the retina: which could not take place without a sensorium or
center of union of the nerves of the iris with those of vision. See
Botanic Garden, Part I. Canto 3. l. 440. note.

Besides these organs of sense, which distinguish cold, moisture, and
darkness, the leaves of mimosa, and of dionæa, and of drosera, and the
stamens of many flowers, as of the berbery, and the numerous class of
syngenesia, are sensible to mechanic impact, that is, they possess a
sense of touch, as well as a common sensorium; by the medium of which
their muscles are excited into action. Lastly, in many flowers the
anthers, when mature, approach the stigma, in others the female organ
approaches to the male. In a plant of collinsonia, a branch of which is
now before me, the two yellow stamens are about three eights of an inch
high, and diverge from each other, at an angle of about fifteen degrees,
the purple style is half an inch high, and in some flowers is now applied
to the stamen on the right hand, and in others to that of the left; and
will, I suppose, change place to-morrow in those, where the anthers have
not yet effused their powder.

I ask, by what means are the anthers in many flowers, and stigmas in
other flowers, directed to find their paramours? How do either of them
know, that the other exists in their vicinity? Is this curious kind of
storge produced by mechanic attraction, or by the sensation of love? The
latter opinion is supported by the strongest analogy, because a
reproduction of the species is the consequence; and then another organ of
sense must be wanted to direct these vegetable amourettes to find each
other, one probably analogous to our sense of smell, which in the animal
world directs the new-born infant to its source of nourishment, and they
may thus possess a faculty of perceiving as well as of producing
odours.

Thus, besides a kind of taste at the extremities of their roots,
similar to that of the extremities of our lacteal vessels, for the
purpose of selecting their proper food: and besides different kinds of
irritability residing in the various glands, which separate honey, wax,
resin, and other juices from their blood; vegetable life seems to possess
an organ of sense to distinguish the variations of heat, another to
distinguish the varying degrees of moisture, another of light, another of
touch, and probably another analogous to our sense of smell. To these
must be added the indubitable evidence of their passion of love, and I
think we may truly conclude, that they are furnished with a common
sensorium belonging to each bud and that they must occasionally repeat
those perceptions either in their dreams or waking hours, and
consequently possess ideas of so many of the properties of the external
world, and of their own existence.

SECT. XIV.

OF THE PRODUCTION OF IDEAS.

I. Of material and immaterial beings.
Doctrine of St. Paul. II. 1. Of the sense of touch. Of solidity. 2. Of figure. Motion. Time. Place. Space.
Number. 3. Of the penetrability of
matter. 4. Spirit of animation
possesses solidity, figure, visibility, &c. Of Spirits and
angels. 5. The existence of external
things. III. Of vision. IV. Of hearing. V. Of smell and taste. VI. Of the organ of sense by which we perceive
heat and cold, not by the sense of touch. VII. Of the sense of extension, the whole of
the locomotive muscles may be considered as one organ of sense. VIII. Of the senses of hunger, thirst, want of
fresh air, suckling children, and lust. IX.
Of many other organs of sense belonging to the glands. Of painful
sensations from the excess of light, pressure, heat, itching, caustics,
and electricity.

I. Philosophers have been much perplexed to
understand, in what manner we become acquainted with the external world;
insomuch that Dr. Berkly even doubted its existence, from having observed
(as he thought) that none of our ideas resemble their correspondent
objects. Mr. Hume asserts, that our belief depends on the greater
distinctness or energy of our ideas from perception; and Mr. Reid has
lately contended, that our belief of external objects is an innate
principle necessarily joined with our perceptions.

So true is the observation of the famous Malbranch, “that our senses
are not given us to discover the essences of things, but to acquaint us
with the means of preserving our existence,” (L. I. ch. v.) a melancholy
reflection to philosophers!

Some philosophers have divided all created beings into material and
immaterial: the former including all that part of being, which obeys the
mechanic laws of action and reaction, but which can begin no motion of
itself; the other is the cause of all motion, and is either termed the
power of gravity, or of specific attraction, or the spirit of animation.
This immaterial agent is supposed to exist in or with matter, but to be
quite distinct from it, and to be equally capable of existence, after the
matter, which now possesses it, is decomposed.

Nor is this theory ill supported by analogy, since heat, electricity,
and magnetism, can be given to or taken from a piece of iron; and must
therefore exist, whether separated from the metal, or combined with it.
From a parity of reasoning, the spirit of animation, would appear to be
capable of existing as well separately from the body as with it.

I beg to be understood, that I do not wish to dispute about words, and
am ready to allow, that the powers of gravity, specific attraction,
electricity, magnetism, and even the spirit of animation, may consist of
matter of a finer kind; and to believe, with St. Paul and Malbranch, that
the ultimate cause only of all motion is immaterial, that is God. St.
Paul says, “in him we live and move, and have our being;” and, in the
15th chapter to the Corinthians, distinguishes between the psyche or
living spirit, and the pneuma or reviving spirit. By the words spirit of
animation or sensorial power, I mean only that animal life, which mankind
possesses in common with brutes, and in some degree even with vegetables,
and leave the consideration of the immortal part of us, which is the
object of religion, to those who treat of revelation.

II. 1. Of the Sense of Touch.

The first idea we become acquainted with, are those of the sense of
touch; for the fœtus must experience some varieties of agitation,
and exert some muscular action, in the womb; and may with great
probability be supposed thus to gain some ideas of its own figure, of
that of the uterus, and of the tenacity of the fluid, that surrounds it,
(as appears from the facts mentioned in the succeeding Section upon
Instinct.)

Many of the organs of sense are confined to a small part of the body,
as the nostrils, ear, or eye, whilst the sense of touch is diffused over
the whole skin, but exists with a more exquisite degree of delicacy at
the extremities of the fingers and thumbs, and in the lips. The sense of
touch is thus very commodiously disposed for the purpose of encompassing
smaller bodies, and for adapting itself to the inequalities of larger
ones. The figure of small bodies seems to be learnt by children by their
lips as much as by their fingers; on which account they put every new
object to their mouths, when they are satiated with food, as well as when
they are hungry. And puppies seem to learn their ideas of figure
principally by the lips in their mode of play.

We acquire our tangible ideas of objects either by the simple pressure
of this organ of touch against a solid body, or by moving our organ of
touch along the surface of it. In the former case we learn the length and
breadth of the object by the quantity of our organ of touch, that is
impressed by it: in the latter case we learn the length and breadth of
objects by the continuance of their pressure on our moving organ of
touch.

It is hence, that we are very slow in acquiring our tangible ideas,
and very slow in recollecting them; for if I now think of the tangible
idea of a cube, that is, if I think of its figure, and of the solidity of
every part of that figure, I must conceive myself as passing my fingers
over it, and seem in some measure to feel the idea, as I formerly did the
impression, at the ends of them, and am thus very slow in distinctly
recollecting it.

When a body compresses any part of our sense of touch, what happens?
First, this part of our sensorium undergoes a mechanical compression,
which is termed a stimulus; secondly, an idea, or contraction of a part
of the organ of sense is excited; thirdly, a motion of the central parts,
or of the whole sensorium, which is termed sensation, is produced; and
these three constitute the perception of solidity.

2. Of Figure, Motion, Time, Place, Space, Number.

No one will deny, that the medulla of the brain and nerves has a
certain figure; which, as it is diffused through nearly the whole of the
body, must have nearly the figure of that body. Now it follows, that the
spirit of animation, or living principle, as it occupies this medulla,
and no other part, (which is evinced by a great variety of cruel
experiments on living animals,) it follows, that this spirit of animation
has also the same figure as the medulla above described. I appeal to
common sense! the spirit of animation acts, Where does it act? It acts
wherever there is the medulla above mentioned; and that whether the limb
is yet joined to a living animal, or whether it be recently detached from
it; as the heart of a viper or frog will renew its contractions, when
pricked with a pin, for many minutes of time after its exsection from the
body.—Does it act any where else?—No; then it certainly
exists in this part of space, and no where else; that is, it hath figure;
namely, the figure of the nervous system, which is nearly the figure of
the body. When the idea of solidity is excited, as above explained, a
part of the extensive organ of touch is compressed by some external body,
and this part of the sensorium so compressed exactly resembles in
figure the figure of the body that compressed it. Hence, when we
acquire the idea of solidity, we acquire at the same time the idea of
FIGURE; and this idea of figure, or motion of
a part of the organ of touch, exactly resembles in its
figure the figure of the body that occasions it; and thus exactly
acquaints us with this property of the external world.

Now, as the whole universe with all its parts possesses a certain form
or figure, if any part of it moves, that form or figure of the whole is
varied: hence, as MOTION is no other than a
perpetual variation of figure, our idea of motion is also a real
resemblance of the motion that produced it.

It may be said in objection to this definition of motion, that an
ivory globe may revolve on its axis, and that here will be a motion
without change of figure. But the figure of the particle x on one
side of this globe is not the same figure as the figure of
y on the other side, any more than the particles themselves are
the same, though they are similar figures; and hence they cannot
change place with each other without disturbing or changing the figure of
the whole.

Our idea of TIME is from the same source, but
is more abstracted, as it includes only the comparative velocities of
these variations of figure; hence if it be asked, How long was this book
in printing? it may be answered, Whilst the sun was passing through
Aries.

Our idea of PLACE includes only the figure of
a group of bodies, not the figures of the bodies themselves. If it be
asked where is Nottinghamshire, the answer is, it is surrounded by
Derbyshire, Lincolnshire and Leicestershire; hence place is our idea of
the figure of one body surrounded by the figures of other bodies.

The idea of SPACE is a more abstracted idea of
place excluding the group of bodies.

The idea of NUMBER includes only the
particular arrangements, or distributions of a group of bodies, and is
therefore only a more abstracted idea of the parts of the figure of the
group of bodies; thus when I say England is divided into forty counties,
I only speak of certain divisions of its figure.

Hence arises the certainty of the mathematical sciences, as they
explain these properties of bodies, which are exactly resembled by our
ideas of them, whilst we are obliged to collect almost all our other
knowledge from experiment; that is, by observing the effects exerted by
one body upon another.

3. Of the Penetrability of Matter.

The impossibility of two bodies existing together in the same space
cannot be deduced from our idea of solidity, or of figure. As soon as we
perceive the motions of objects that surround us, and learn that we
possess a power to move our own bodies, we experience, that those
objects, which excite in us the idea of solidity and of figure, oppose
this voluntary movement of our own organs; as whilst I endeavour to
compress between my hands an ivory ball into a spheroid. And we are hence
taught by experience, that our own body and those, which we touch, cannot
exist in the same part of space.

But this by no means demonstrates, that no two bodies can exist
together in the same part of space. Galilæo in the preface to his works
seems to be of opinion, that matter is not impenetrable; Mr. Michel, and
Mr. Boscowich in his Theoria. Philos. Natur. have espoused this
hypothesis: which has been lately published by Dr. Priestley, to whom the
world is much indebted for so many important discoveries in science.
(Hist. of Light and Colours, p. 391.) The uninterrupted passage of light
through transparent bodies, of the electric æther through metallic and
aqueous bodies, and of the magnetic effluvia through all bodies, would
seem to give some probability to this opinion. Hence it appears, that
beings may exist without possessing the property of solidity, as well as
they can exist without possessing the properties, which excite our smell
or taste, and can thence occupy space without detruding other bodies from
it; but we cannot become acquainted with such beings by our sense of
touch, any more than we can with odours or flavours without our senses of
smell and taste.

But that any being can exist without existing in space, is to my ideas
utterly incomprehensible. My appeal is to common sense. To be
implies a when and a where; the one is comparing it with the motions of
other beings, and the other with their situations.

If there was but one object, as the whole creation may be considered
as one object, then I cannot ask where it exists? for there are no other
objects to compare its situation with. Hence if any one denies, that a
being exists in space, he denies, that there are any other beings but
that one; for to answer the question, “Where does it exist?” is only to
mention the situation of the objects that surround it.

In the same manner if it be asked—”When does a being exist?” The
answer only specifies the successive motions either of itself, or of
other bodies; hence to say, a body exists not in time, is to say, that
there is, or was, no motion in the world.

4. Of the Spirit of Animation.

But though there may exist beings in the universe, that have not the
property of solidity; that is, which can possess any part of space, at
the same time that it is occupied by other bodies; yet there may be other
beings, that can assume this property of solidity, or disrobe themselves
of it occasionally, as we are taught of spirits, and of angels; and it
would seem, that THE SPIRIT OF ANIMATION must be
endued with this property, otherwise how could it occasionally give
motion to the limbs of animals?—or be itself stimulated into motion
by the obtrusions of surrounding bodies, as of light, or odour?

If the spirit of animation was always necessarily penetrable, it could
not influence or be influenced by the solidity of common matter; they
would exist together, but could not detrude each other from the part of
space, where they exist; that is, they could not communicate motion to
each other. No two things can influence or affect each other, which
have not some property common to both of them; for to influence or
affect another body is to give or communicate some property to it, that
it had not before; but how can one body give that to another, which it
does not possess itself?—The words imply, that they must agree in
having the power or faculty of possessing some common property. Thus if
one body removes another from the part of space, that it possesses, it
must have the power of occupying that space itself: and if one body
communicates heat or motion to another, it follows, that they have alike
the property of possessing heat or motion.

Hence the spirit of animation at the time it communicates or receives
motion from solid bodies, must itself possess some property of solidity.
And in consequence at the time it receives other kinds of motion from
light, it must possess that property, which light possesses, to
communicate that kind of motion; and for which no language has a name,
unless it may be termed Visibility. And at the time it is stimulated into
other kinds of animal motion by the particles of sapid and odorous bodies
affecting the senses of taste and smell, it must resemble these particles
of flavour, and of odour, in possessing some similar or correspondent
property; and for which language has no name, unless we may use the words
Saporosity and Odorosity for those common properties, which are possessed
by our organs of taste and smell, and by the particles of sapid and
odorous bodies; as the words Tangibility and Audibility may express the
common property possessed by our organs of touch, and of hearing, and by
the solid bodies, or their vibrations, which affect those organs.

5. Finally, though the figures of bodies
are in truth resembled by the figure of the part of the organ of touch,
which is stimulated into motion; and that organ resembles the solid body,
which stimulates it, in its property of solidity; and though the sense of
hearing resembles the vibrations of external bodies in its capability of
being stimulated into motion by those vibrations; and though our other
organs of sense resemble the bodies, that stimulate them, in their
capability of being stimulated by them; and we hence become acquainted
with these properties of the external world; yet as we can repeat all
these motions of our organs of sense by the efforts of volition, or in
consequence of the sensation of pleasure or pain, or by their association
with other fibrous motions, as happens in our reveries or in sleep, there
would still appear to be some difficulty in demonstrating the existence
of any thing external to us.

In our dreams we cannot determine this circumstance, because our power
of volition is suspended, and the stimuli of external objects are
excluded; but in our waking hours we can compare our ideas belonging to
one sense with those belonging to another, and can thus distinguish the
ideas occasioned by irritation from those excited by sensation, volition,
or association. Thus if the idea of the sweetness of sugar should be
excited in our dreams, the whiteness and hardness of it occur at the same
time by association; and we believe a material lump of sugar present
before us. But if, in our waking hours, the idea of the sweetness of
sugar occurs to us, the stimuli of surrounding objects, as the edge of
the table, on which we press, or green colour of the grass, on which we
tread, prevent the other ideas of the hardness and whiteness of the sugar
from being exerted by association. Or if they should occur, we
voluntarily compare them with the irritative ideas of the table or grass
above mentioned, and detect their fallacy. We can thus distinguish the
ideas caused by the stimuli of external objects from those, which are
introduced by association, sensation, or volition; and during our waking
hours can thus acquire a knowledge of the external world. Which
nevertheless we cannot do in our dreams, because we have neither
perceptions of external bodies, nor the power of volition to enable us to
compare them with the ideas of imagination.

III. Of Vision.

Our eyes observe a difference of colour, or of shade, in the
prominences and depressions of objects, and that those shades uniformly
vary, when the sense of touch observes any variation. Hence when the
retina becomes stimulated by colours or shades of light in a certain
form, as in a circular spot; we know by experience, that this is a sign,
that a tangible body is before us; and that its figure is resembled by
the miniature figure of the part of the organ of vision, that is thus
stimulated.

Here whilst the stimulated part of the retina resembles exactly the
visible figure of the whole in miniature, the various kinds of stimuli
from different colours mark the visible figures of the minuter parts; and
by habit we instantly recall the tangible figures.

Thus when a tree is the object of sight, a part of the retina
resembling a flat branching figure is stimulated by various shades of
colours; but it is by suggestion, that the gibbosity of the tree, and the
moss, that fringes its trunk, appear before us. These are ideas of
suggestion, which we feel or attend to, associated with the motions of
the retina, or irritative ideas, which we do not attend to.

So that though our visible ideas resemble in miniature the outline of
the figure of coloured bodies, in other respects they serve only as a
language, which by acquired associations introduce the tangible ideas of
bodies. Hence it is, that this sense is so readily deceived by the art of
the painter to our amusement and instruction. The reader will find much
very curious knowledge on this subject in Bishop Berkley’s Essay on
Vision, a work of great ingenuity.

The immediate object however of the sense of vision is light; this
fluid, though its velocity is so great, appears to have no perceptible
mechanical impulse, as was mentioned in the third Section, but seems to
stimulate the retina into animal motion by its transmission through this
part of the sensorium: for though the eyes of cats or other animals
appear luminous in obscure places; yet it is probable, that none of the
light, which falls on the retina, is reflected from it, but adheres to or
enters into combination with the choroide coat behind it.

The combination of the particles of light with opake bodies, and
therefore with the choroide coat of the eye, is evinced from the heat,
which is given out, as in other chemical combinations. For the sunbeams
communicate no heat in their passage through transparent bodies, with
which they do not combine, as the air continues cool even in the focus of
the largest burning-glasses, which in a moment vitrifies a particle of
opaque matter.

IV. Of the Organ of Hearing.

It is generally believed, that the tympanum of the ear vibrates
mechanically, when exposed to audible sounds, like the strings of one
musical instrument, when the same notes are struck upon another. Nor is
this opinion improbable, as the muscles and cartilages of the larynx are
employed in producing variety of tones by mechanical vibration: so the
muscles and bones of the ear seem adapted to increase or diminish the
tension of the tympanum for the purposes of similar mechanical
vibrations.

But it appears from dissection, that the tympanum is not the immediate
organ of hearing, but that like the humours and cornea of the eye, it is
only of use to prepare the object for the immediate organ. For the portio
mollis of the auditory nerve is not spread upon the tympanum, but upon
the vestibulum, and cochlea, and semicircular canals of the ear; while
between the tympanum and the expansion of the auditory nerve the cavity
is said by Dr. Cotunnus and Dr. Meckel to be filled with water; as they
had frequently observed by freezing the heads of dead animals before they
dissected them; and water being a more dense fluid than air is much
better adapted to the propagation of vibrations. We may add, that even
the external opening of the ear is not absolutely necessary for the
perception of sound: for some people, who from these defects would have
been completely deaf, have distinguished acute or grave sounds by the
tremours of a stick held between their teeth propagated along the bones
of the head, (Haller. Phys. T. V. p. 295).

Hence it appears, that the immediate organ of hearing is not affected
by the particles of the air themselves, but is stimulated into animal
motion by the vibrations of them. And it is probable from the loose
bones, which are found in the heads of some fishes, that the vibrations
of water are sensible to the inhabitants of that element by a similar
organ.

The motions of the atmosphere, which we become acquainted with by the
sense of touch, are combined with its solidity, weight, or vis intertiæ;
whereas those, that are perceived by this organ, depend alone on its
elasticity. But though the vibration of the air is the immediate object
of the sense of hearing, yet the ideas, we receive by this sense, like
those received from light, are only as a language, which by acquired
associations acquaints us with those motions of tangible bodies, which
depend on their elasticity; and which we had before learned by our sense
of touch.

V. Of Smell and of Taste.

The objects of smell are dissolved in the fluid atmosphere, and those
of taste in the saliva, or other aqueous fluid, for the better diffusing
them on their respective organs, which seem to be stimulated into animal
motion perhaps by the chemical affinities of these particles, which
constitute the sapidity and odorosity of bodies with the nerves of sense,
which perceive them.

Mr. Volta has lately observed a curious circumstance relative to our
sense of taste. If a bit of clean lead and a bit of clean silver be
separately applied to the tongue and palate no taste is perceived; but by
applying them in contact in respect to the parts out of the mouth, and
nearly so in respect to the parts, which are immediately applied to the
tongue and palate, a saline or acidulous taste is perceived, as of a
fluid like a stream of electricity passing from one of them to the other.
This new application of the sense of taste deserves further
investigation, as it may acquaint us with new properties of matter.

From the experiments above mentioned of Galvani, Volta, Fowler, and
others, it appears, that a plate of zinc and a plate of silver have
greater effect than lead and silver. If one edge of a plate of silver
about the size of half a crown-piece be placed upon the tongue, and one
edge of a plate of zinc about the same size beneath the tongue, and if
their opposite edges are then brought into contact before the point of
the tongue, a taste is perceived at the moment of their coming into
contact; secondly, if one of the above plates be put between the upper
lip and the gum of the fore-teeth, and the other be placed under the
tongue, and their exterior edges be then brought into contact in a
darkish room, a flash of light is perceived in the eyes.

These effects I imagine only shew the sensibility of our nerves of
sense to very small quantities of the electric fluid, as it passes
through them; for I suppose these sensations are occasioned by slight
electric shocks produced in the following manner. By the experiments
published by Mr. Bennet, with his ingenious doubler of electricity, which
is the greatest discovery made in that science since the coated jar, and
the eduction of lightning from the skies, it appears that zinc was always
found minus, and silver was always found plus, when both of them were in
their separate state. Hence, when they are placed in the manner above
described, as soon as their exterior edges come nearly into contact, so
near as to have an extremely thin plate of air between them, that plate
of air becomes charged in the same manner as a plate of coated glass; and
is at the same instant discharged through the nerves of taste or of
sight, and gives the sensations, as above described, of light or of
saporocity; and only shews the great sensibility of these organs of sense
to the stimulus of the electric fluid in suddenly passing through
them.

VI. Of the Sense of Heat.

There are many experiments in chemical writers, that evince the
existence of heat as a fluid element, which covers and pervades all
bodies, and is attracted by the solutions of some of them, and is
detruded from the combination of others. Thus from the combinations of
metals with acids, and from those combinations of animal fluids, which
are termed secretions, this fluid matter of heat is given out amongst the
neighbouring bodies; and in the solutions of salts in water, or of water
in air, it is absorbed from the bodies, that surround them; whilst in its
facility in passing through metallic bodies, and its difficulty in
pervading resins and glass, it resembles the properties of the electric
aura; and is like that excited by friction, and seems like that to
gravitate amongst other bodies in its uncombined state, and to find its
equilibrium.

There is no circumstance of more consequence in the animal economy
than a due proportion of this fluid of heat; for the digestion of our
nutriment in the stomach and bowels, and the proper qualities of all our
secreted fluids, as they are produced or prepared partly by animal and
partly by chemical processes, depend much on the quantity of heat; the
excess of which, or its deficiency, alike gives us pain, and induces us
to avoid the circumstances that occasion them. And in this the perception
of heat essentially differs from the perceptions of the sense of touch,
as we receive pain from too great pressure of solid bodies, but none from
the absence of it. It is hence probable, that nature has provided us with
a set of nerves for the perception of this fluid, which anatomists have
not yet attended to.

There may be some difficulty in the proof of this assertion; if we
look at a hot fire, we experience no pain of the optic nerve, though the
heat along with the light must be concentrated upon it. Nor does warm
water or warm oil poured into the ear give pain to the organ of hearing;
and hence as these organs of sense do not perceive small excesses or
deficiences of heat; and as heat has no greater analogy to the solidity
or to the figures of bodies, than it has to their colours or vibrations;
there seems no sufficient reason for our ascribing the perception of heat
and cold to the sense of touch; to which it has generally been
attributed, either because it is diffused beneath the whole skin like the
sense of touch, or owing to the inaccuracy of our observations, or the
defect of our languages.

There is another circumstance would induce us to believe, that the
perceptions of heat and cold do not belong to the organ of touch; since
the teeth, which are the least adapted for the perceptions of solidity or
figure, are the most sensible to heat or cold; whence we are forewarned
from swallowing those materials, whose degree of coldness or of heat
would injure our stomachs.

The following is an extract from a letter of Dr. R.W. Darwin, of
Shrewsbury, when he was a student at Edinburgh. “I made an experiment
yesterday in our hospital, which much favours your opinion, that the
sensation of heat and of touch depend on different sets of nerves. A man
who had lately recovered from a fever, and was still weak, was seized
with violent cramps in his legs and feet; which were removed by opiates,
except that one of his feet remained insensible. Mr. Ewart pricked him
with a pin in five or six places, and the patient declared he did not
feel it in the least, nor was he sensible of a very smart pinch. I then
held a red-hot poker at some distance, and brought it gradually nearer
till it came within three inches, when he asserted that he felt it quite
distinctly. I suppose some violent irritation on the nerves of touch had
caused the cramps, and had left them paralytic; while the nerves of heat,
having suffered no increased stimulus, retained their irritability.”

Add to this, that the lungs, though easily stimulated into
inflammation, are not sensible to heat. See Class. III. 1. 1. 10.

VII. Of the Sense of Extension.

The organ of touch is properly the sense of pressure, but the muscular
fibres themselves constitute the organ of sense, that feels extension.
The sense of pressure is always attended with the ideas of the figure and
solidity of the object, neither of which accompany our perception of
extension. The whole set of muscles, whether they are hollow ones, as the
heart, arteries, and intestines, or longitudinal ones attached to bones,
contract themselves, whenever they are stimulated by forcible elongation;
and it is observable, that the white muscles, which constitute the
arterial system, seem to be excited into contraction from no other kinds
of stimulus, according to the experiments of Haller. And hence the
violent pain in some inflammations, as in the paronychia, obtains
immediate relief by cutting the membrane, that was stretched by the
tumour of the subjacent parts.

Hence the whole muscular system may be considered as one organ of
sense, and the various attitudes of the body, as ideas belonging to this
organ, of many of which we are hourly conscious, while many others, like
the irritative ideas of the other senses, are performed without our
attention.

When the muscles of the heart cease to act, the refluent blood again
distends or elongates them; and thus irritated they contract as before.
The same happens to the arterial system, and I suppose to the
capillaries, intestines, and various glands of the body.

When the quantity of urine, or of excrement, distends the bladder, or
rectum, those parts contract, and exclude their contents, and many other
muscles by association act along with them; but if these evacuations are
not soon complied with, pain is produced by a little further extension of
the muscular fibres: a similar pain is caused in the muscles, when a limb
is much extended for the reduction of dislocated bones; and in the
punishment of the rack: and in the painful cramps of the calf of the leg,
or of other muscles, for a greater degree of contraction of a muscle,
than the movement of the two bones, to which its ends are affixed, will
admit of, must give similar pain to that, which is produced by extending
it beyond its due length. And the pain from punctures or incisions arises
from the distention of the fibres, as the knife passes through them; for
it nearly ceases as soon as the division is completed.

All these motions of the muscles, that are thus naturally excited by
the stimulus of distending bodies, are also liable to be called into
strong action by their catenation, with the irritations or sensations
produced by the momentum of the progressive particles of blood in the
arteries, as in inflammatory fevers, or by acrid substances on other
sensible organs, as in the strangury, or tenesmus, or cholera.

We shall conclude this account of the sense of extension by observing,
that the want of its object is attended with a disagreeable sensation, as
well as the excess of it. In those hollow muscles, which have been
accustomed to it, this disagreeable sensation is called faintness,
emptiness, and sinking; and, when it arises to a certain degree, is
attended with syncope, or a total quiescence of all motions, but the
internal irritative ones, as happens from sudden loss of blood, or in the
operation of tapping in the dropsy.

VIII. Of the Appetites of Hunger, Thirst, Heat, Extension, the want
of fresh Air, animal Love, and the Suckling of Children.

Hunger is most probably perceived by those numerous ramifications of
nerves that are seen about the upper opening of the stomach; and thirst
by the nerves about the fauces, and the top of the gula. The ideas of
these senses are few in the generality of mankind, but are more numerous
in those, who by disease, or indulgence, desire particular kinds of foods
or liquids.

A sense of heat has already been spoken of, which may with propriety
be called an appetite, as we painfully desire it, when it is deficient in
quantity.

The sense of extension may be ranked amongst these appetites, since
the deficiency of its object gives disagreeable sensation; when this
happens in the arterial system, it is called faintness, and seems to bear
some analogy to hunger and to cold; which like it are attended with
emptiness of a part of the vascular system.

The sense of want of fresh air has not been attended to, but is as
distinct as the others, and the first perhaps that we experience after
our nativity; from the want of the object of this sense many diseases are
produced, as the jail-fever, plague, and other epidemic maladies. Animal
love is another appetite, which occurs later in life, and the females of
lactiferous animals have another natural inlet of pleasure or pain from
the suckling their offspring. The want of which either owing to the death
of their progeny, or to the fashion of their country, has been fatal to
many of the sex. The males have also pectoral glands, which are
frequently turgid with a thin milk at their nativity, and are furnished
with nipples, which erect on titillation like those of the female; but
which seem now to be of no further use, owing perhaps to some change
which these animals have undergone in the gradual progression of the
formation of the earth, and of all that it inhabit.

These seven last mentioned senses may properly be termed appetites, as
they differ from those of touch, sight, hearing, taste, and smell, in
this respect; that they are affected with pain as well by the defect of
their objects as by the excess of them, which is not so in the latter.
Thus cold and hunger give us pain, as well as an excess of heat or
satiety; but it is not so with darkness and silence.

IX. Before we conclude this Section on the
organs of sense, we must observe, that, as far as we know, there are many
more senses, than have been here mentioned, as every gland seems to be
influenced to separate from the blood, or to absorb from the cavities of
the body, or from the atmosphere, its appropriated fluid, by the stimulus
of that fluid on the living gland; and not by mechanical capillary
absorption, nor by chemical affinity. Hence it appears, that each of
these glands must have a peculiar organ to perceive these irritations,
but as these irritations are not succeeded by sensation, they have not
acquired the names of senses.

However when these glands are excited into motions stronger than
usual, either by the acrimony of their fluids, or by their own
irritability being much increased, then the sensation of pain is produced
in them as in all the other senses of the body; and these pains are all
of different kinds, and hence the glands at this time really become each
a different organ of sense, though these different kinds of pain have
acquired no names.

Thus a great excess of light does not give the idea of light but of
pain; as in forcibly opening the eye when it is much inflamed. The great
excess of pressure or distention, as when the point of a pin is pressed
upon our skin, produces pain, (and when this pain of the sense of
distention is slighter, it is termed itching, or tickling), without any
idea of solidity or of figure: an excess of heat produces smarting, of
cold another kind of pain; it is probable by this sense of heat the pain
produced by caustic bodies is perceived, and of electricity, as all these
are fluids, that permeate, distend, or decompose the parts that feel
them.

SECT. XV.

OF THE CLASSES OF IDEAS.

I. 1. Ideas
received in tribes. 2. We combine them
further, or abstract from these tribes. 3.
Complex ideas. 4. Compounded
ideas. 5. Simple ideas, modes,
substances, relations, general ideas. 6.
Ideas of reflexion. 7. Memory and
imagination imperfectly defined. Ideal presence. Memorandum-rings. II. 1. Irritative
ideas. Perception. 2. Sensitive ideas,
imagination. 3. Voluntary ideas,
recollection. 4. Associated ideas,
suggestion. III. 1. Definitions of perception, memory. 2. Reasoning, judgment, doubting,
distinguishing, comparing. 3.
Invention. 4. Consciousness. 5. Identity. 6.
Lapse of time. 7. Free-will.

I. 1. As the
constituent elements of the material world are only perceptible to our
organs of sense in a state of combination; it follows, that the ideas or
sensual motions excited by them, are never received singly, but ever with
a greater or less degree of combination. So the colours of bodies or
their hardnesses occur with their figures: every smell and taste has its
degree of pungency as well as its peculiar flavour: and each note in
music is combined with the tone of some instrument. It appears from
hence, that we can be sensible of a number of ideas at the same time,
such as the whiteness, hardness, and coldness, of a snow-ball, and can
experience at the same time many irritative ideas of surrounding bodies,
which we do not attend to, as mentioned in Section VII. 3. 2. But those ideas which belong to the
same sense, seem to be more easily combined into synchronous tribes, than
those which were not received by the same sense, as we can more easily
think of the whiteness and figure of a lump of sugar at the same time,
than the whiteness and sweetness of it.

2. As these ideas, or sensual motions, are
thus excited with greater or less degrees of combination; so we have a
power, when we repeat them either by our volition or sensation, to
increase or diminish this degree of combination, that is, to form
compounded ideas from those, which were more simple; and abstract ones
from those, which were more complex, when they were first excited; that
is, we can repeat a part or the whole of those sensual motions, which did
constitute our ideas of perception; and the repetition of which now
constitutes our ideas of recollection, or of imagination.

3. Those ideas, which we repeat without
change of the quantity of that combination, with which we first received
them, are called complex ideas, as when you recollect Westminster Abbey,
or the planet Saturn: but it must be observed, that these complex ideas,
thus re-excited by volition, sensation, or association, are seldom
perfect copies of their correspondent perceptions, except in our dreams,
where other external objects do not detract our attention.

4. Those ideas, which are more complex than
the natural objects that first excited them, have been called compounded
ideas, as when we think of a sphinx, or griffin.

5. And those that are less complex than the
correspondent natural objects, have been termed abstracted ideas: thus
sweetness, and whiteness, and solidity, are received at the same time
from a lump of sugar, yet I can recollect any of these qualities without
thinking of the others, that were excited along with them.

When ideas are so far abstracted as in the above example, they have
been termed simple by the writers of metaphysics, and seem indeed to be
more complete repetitions of the ideas or sensual motions, originally
excited by external objects.

Other classes of these ideas, where the abstraction has not been so
great, have been termed, by Mr. Locke, modes, substances, and relations,
but they seem only to differ in their degree of abstraction from the
complex ideas that were at first excited; for as these complex or natural
ideas are themselves imperfect copies of their correspondent perceptions,
so these abstract or general ideas are only still more imperfect copies
of the same perceptions. Thus when I have seen an object but once, as a
rhinoceros, my abstract idea of this animal is the same as my complex
one. I may think more or less distinctly of a rhinoceros, but it is the
very rhinoceros that I saw, or some part or property of him, which recurs
to my mind.

But when any class of complex objects becomes the subject of
conversation, of which I have seen many individuals, as a castle or an
army, some property or circumstance belonging to it is peculiarly alluded
to; and then I feel in my own mind, that my abstract idea of this complex
object is only an idea of that part, property, or attitude of it, that
employs the present conversation, and varies with every sentence that is
spoken concerning it. So if any one should say, “one may sit upon a horse
safer than on a camel,” my abstract idea of the two animals includes only
an outline of the level back of the one, and the gibbosity on the back of
the other. What noise is that in the street?—Some horses trotting
over the pavement. Here my idea of the horses includes principally the
shape and motion of their legs. So also the abstract ideas of goodness
and courage are still more imperfect representations of the objects they
were received from; for here we abstract the material parts, and
recollect only the qualities.

Thus we abstract so much from some of our complex ideas, that at
length it becomes difficult to determine of what perception they partake;
and in many instances our idea seems to be no other than of the sound or
letters of the word, that stands for the collective tribe, of which we
are said to have an abstracted idea, as noun, verb, chimæra,
apparition.

6. Ideas have been divided into those of
perception and those of reflection, but as whatever is perceived must be
external to the organ that perceives it, all our ideas must originally be
ideas of perception.

7. Others have divided our ideas into those
of memory, and those of imagination; they have said that a recollection
of ideas in the order they were received constitutes memory, and without
that order imagination; but all the ideas of imagination, excepting the
few that are termed simple ideas, are parts of trains or tribes in the
order they were received; as if I think of a sphinx, or a griffin, the
fair face, bosom, wings, claws, tail, are all complex ideas in the order
they were received: and it behoves the writers, who adhere to this
definition, to determine, how small the trains must be, that shall be
called imagination; and how great those, that shall be called memory.

Others have thought that the ideas of memory have a greater vivacity
than those of imagination: but the ideas of a person in sleep, or in a
waking reverie, where the trains connected with sensation are
uninterrupted, are more vivid and distinct than those of memory, so that
they cannot be distinguished by this criterion.

The very ingenious author of the Elements of Criticism has described
what he conceives to be a species of memory, and calls it ideal presence;
but the instances he produces are the reveries of sensation, and are
therefore in truth connections of the imagination, though they are
recalled in the order they were received.

The ideas connected by association are in common discourse attributed
to memory, as we talk of memorandum-rings, and tie a knot on our
handkerchiefs to bring something into our minds at a distance of time.
And a school-boy, who can repeat a thousand unmeaning lines in Lilly’s
Grammar, is said to have a good memory. But these have been already shewn
to belong to the class of association; and are termed ideas of
suggestion.

II. Lastly, the method already explained of
classing ideas into those excited by irritation, sensation, volition, or
association, we hope will be found more convenient both for explaining
the operations of the mind, and for comparing them with those of the
body; and for the illustration and the cure of the diseases of both, and
which we shall here recapitulate.

1. Irritative ideas are those, which are
preceded by irritation, which is excited by objects external to the
organs of sense: as the idea of that tree, which either I attend to, or
which I shun in walking near it without attention. In the former case it
is termed perception, in the latter it is termed simply an irritative
idea.

2. Sensitive ideas are those, which are
preceded by the sensation of pleasure or pain; as the ideas, which
constitute our dreams or reveries, this is called imagination.

3. Voluntary ideas are those, which are
preceded by voluntary exertion, as when I repeat the alphabet backwards:
this is called recollection.

4. Associate ideas are those, which are
preceded by other ideas or muscular motions, as when we think over or
repeat the alphabet by rote in its usual order; or sing a tune we are
accustomed to; this is called suggestion.

III. 1. Perceptions
signify those ideas, which are preceded by irritation and succeeded by
the sensation of pleasure or pain, for whatever excites our attention
interests us; that is, it is accompanied with, pleasure or pain; however
slight may be the degree or quantity of either of them.

The word memory includes two classes of ideas, either those which, are
preceded by voluntary exertion, or those which are suggested by their
associations with other ideas.

2. Reasoning is that operation of the
sensorium, by which we excite two or many tribes of ideas; and then
re-excite the ideas, in which they differ, or correspond. If we determine
this difference, it is called judgment; if we in vain endeavour to
determine it, it is called doubting.

If we re-excited the ideas, in which they differ, it is called
distinguishing. If we re-excite those in which they correspond, it is
called comparing.

3. Invention is an operation of the
sensorium, by which we voluntarily continue to excite one train of ideas,
suppose the design of raising water by a machine; and at the same time
attend to all other ideas, which are connected with this by every kind of
catenation; and combine or separate them voluntarily for the purpose of
obtaining some end.

For we can create nothing new, we can only combine or separate the
ideas, which we have already received by our perceptions: thus if I wish
to represent a monster, I call to my mind the ideas of every thing
disagreeable and horrible, and combine the nastiness and gluttony of a
hog, the stupidity and obstinacy of an ass, with the fur and awkwardness
of a bear, and call the new combination Caliban. Yet such a monster may
exist in nature, as all his attributes are parts of nature. So when I
wish to represent every thing, that is excellent, and amiable; when I
combine benevolence with cheerfulness, wisdom, knowledge, taste, wit,
beauty of person, and elegance of manners, and associate them in one lady
as a pattern to the world, it is called invention; yet such a person may
exist,—such a person does exist!—It is ——
——, who is as much a monster as Caliban.

4. In respect to consciousness, we are only
conscious of our existence, when we think about it; as we only perceive
the lapse of time, when we attend to it; when we are busied about other
objects, neither the lapse of time nor the consciousness of our own
existence can occupy our attention. Hence, when we think of our own
existence, we only excite abstracted or reflex ideas (as they are
termed), of our principal pleasures or pains, of our desires or
aversions, or of the figure, solidity, colour, or other properties of our
bodies, and call that act of the sensorium a consciousness of our
existence. Some philosopher, I believe it is Des Cartes, has said, “I
think, therefore I exist.” But this is not right reasoning, because
thinking is a mode of existence; and it is thence only saying, “I exist,
therefore I exist.” For there are three modes of existence, or in the
language of grammarians three kinds of verbs. First, simply I am, or
exist. Secondly, I am acting, or exist in a state of activity, as I move.
Thirdly, I am suffering, or exist in a state of being acted upon, as I am
moved. The when, and the where, as applicable to this existence, depends
on the successive motions of our own or of other bodies; and on their
respective situations, as spoken of Sect. XIV. 2.
5.

5. Our identity is known by our acquired
habits or catenated trains of ideas and muscular motions; and perhaps,
when we compare infancy with old age, in those alone can our identity be
supposed to exist. For what else is there of similitude between the first
speck of living entity and the mature man?—every deduction of
reasoning, every sentiment or passion, with every fibre of the corporeal
part of our system, has been subject almost to annual mutation; while
some catenations alone of our ideas and muscular actions have continued
in part unchanged.

By the facility, with which we can in our waking hours voluntarily
produce certain successive trains of ideas, we know by experience, that
we have before reproduced them; that is, we are conscious of a time of
our existence previous to the present time; that is, of our identity now
and heretofore. It is these habits of action, these catenations of ideas
and muscular motions, which begin with life, and only terminate with it;
and which we can in some measure deliver to our posterity; as explained
in Sect. XXXIX.

6. When the progressive motions of external
bodies make a part of our present catenation of ideas, we attend to the
lapse of time; which appears the longer, the more frequently we thus
attend to it; as when we expect something at a certain hour, which much
interests us, whether it be an agreeable or disagreeable event; or when
we count the passing seconds on a stop-watch.

When an idea of our own person, or a reflex idea of our pleasures and
pains, desires and aversions, makes a part of this catenation, it is
termed consciousness; and if this idea of consciousness makes a part of a
catenation, which we excite by recollection, and know by the facility
with which we excite it, that we have before experienced it, it is called
identity, as explained above.

7. In respect to freewill, it is certain,
that we cannot will to think of a new train of ideas, without previously
thinking of the first link of it; as I cannot will to think of a black
swan, without previously thinking of a black swan. But if I now think of
a tail, I can voluntarily recollect all animals, which have tails; my
will is so far free, that I can pursue the ideas linked to this idea of
tail, as far as my knowledge of the subject extends; but to will without
motive is to will without desire or aversion; which is as absurd as to
feel without pleasure or pain; they are both solecisms in the terms. So
far are we governed by the catenations of motions, which affect both the
body and the mind of man, and which begin with our irritability, and end
with it.

SECT. XVI.

OF INSTINCT.

I. Instinctive actions defined. Of
connate passions. II. Of the sensations
and motions of the fœtus in the womb. III. Some animals are more perfectly formed
than others before nativity. Of learning to walk. IV. Of the swallowing, breathing, sucking,
pecking, and lapping of young animals. V.
Of the sense of smell, and its uses to animals. Why cats do not eat
their kittens. VI. Of the accuracy of
sight in mankind, and their sense of beauty. Of the sense of touch in
elephants, monkies, beavers, men. VII.
Of natural language. VIII. The origin
of natural language; 1. the language
of fear; 2. of grief; 3. of tender pleasure; 4. of serene pleasure; 5. of anger; 6. of attention. IX. Artificial language of turkies, hens,
ducklings, wagtails, cuckoos, rabbits, dogs, and nightingales. X. Of music; of tooth-edge; of a good ear; of
architecture. XI. Of acquired
knowledge; of foxes, rooks, fieldfares, lapwings, dogs, cats, horses,
crows, and pelicans. XII. Of birds of
passage, dormice, snakes, bats, swallows, quails, ringdoves, stare,
chaffinch, hoopoe, chatterer, hawfinch, crossbill, rails and cranes.
XIII. Of birds nests; of the cuckoo; of
swallows nests; of the taylor bird. XIV.
Of the old soldier; of haddocks, cods, and dog fish; of the remora; of
crabs, herrings, and salmon. XV. Of
spiders, caterpillars, ants, and the ichneumon. XVI. 1. Of
locusts, gnats; 2. bees; 3. dormice, flies, worms, ants, and
wasps. XVII. Of the faculty that
distinguishes man from the brutes.

I. All those internal motions of animal
bodies, which contribute to digest their aliment, produce their
secretions, repair their injuries, or increase their growth, are
performed without our attention or consciousness. They exist as well in
our sleep, as in our waking hours, as well in the fœtus during the
time of gestation, as in the infant after nativity, and proceed with
equal regularity in the vegetable as in the animal system. These motions
have been shewn in a former part of this work to depend on the
irritations of peculiar fluids, and as they have never been classed
amongst the instinctive actions of animals, are precluded from our
present disquisition.

But all those actions of men or animals, that are attended with
consciousness, and seem neither to have been directed by their appetites,
taught by their experience, nor deduced from observation or tradition,
have been referred to the power of instinct. And this power has been
explained to be a divine something, a kind of inspiration; whilst
the poor animal, that possesses it, has been thought little better than
a machine!

The irksomeness, that attends a continued attitude of the body,
or the pains, that we receive from heat, cold, hunger, or other
injurious circumstances, excite us to general locomotion: and our
senses are so formed and constituted by the hand of nature, that certain
objects present us with pleasure, others with pain, and we are induced to
approach and embrace these, to avoid and abhor those, as such sensations
direct us.

Thus the palates of some animals are gratefully affected by the
mastication of fruits, others of grains, and others of flesh; and they
are thence instigated to attain, and to consume those materials; and are
furnished with powers of muscular motion, and of digestion proper for
such purposes.

These sensations and desires constitute a part of our
system, as our muscles and bones constitute another part:
and hence they may alike be termed natural or connate; but
neither of them can properly be termed instinctive: as the word
instinct in its usual acceptation refers only to the actions of
animals, as above explained: the origin of these actions is the
subject of our present enquiry.

The reader is intreated carefully to attend to this definition of
instinctive actions, lest by using the word instinct without
adjoining any accurate idea to it, he may not only include the natural
desires of love and hunger, and the natural sensations of pain or
pleasure, but the figure and contexture of the body, and the faculty of
reason itself under this general term.

II. We experience some sensations, and
perform some actions before our nativity; the sensations of cold and
warmth, agitation and rest, fulness and inanition, are instances of the
former; and the repeated struggles of the limbs of the fœtus, which
begin about the middle of gestation, and those motions by which it
frequently wraps the umbilical chord around its neck or body, and even
sometimes ties it on a knot; are instances of the latter. Smellie’s
Midwifery, (Vol. I. p. 182.)

By a due attention to these circumstances many of the actions of young
animals, which at first sight seemed only referable to an inexplicable
instinct, will appear to have been acquired like all other animal
actions, that are attended with consciousness, by the repeated efforts
of our muscles under the conduct of our sensations or desires.

The chick in the shell begins to move its feet and legs on the sixth
day of incubation (Mattreican, p. 138); or on the seventh day, (Langley);
afterwards they are seen to move themselves gently in the liquid that
surrounds them, and to open and shut their mouths, (Harvei, de Generat.
p. 62, and 197. Form de Poulet. ii. p. 129). Puppies before the membranes
are broken, that involve them, are seen to move themselves, to put out
their tongues, and to open and shut their mouths, (Harvey, Gipson,
Riolan, Haller). And calves lick themselves and swallow many of their
hairs before their nativity: which however puppies do not, (Swammerden,
p. 319. Flemyng Phil. Trans. Ann. 1755. 42). And towards the end of
gestation, the fœtus of all animals are proved to drink part of the
liquid in which they swim, (Haller. Physiol. T. 8. 204). The white of egg
is found in the mouth and gizzard of the chick, and is nearly or quite
consumed before it is hatched, (Harvie de Generat. 58). And the liquor
amnii is found in the mouth and stomach of the human fœtus, and of
calves; and how else should that excrement be produced in the intestines
of all animals, which is voided in great quantity soon after their birth;
(Gipson, Med. Essays, Edinb. V. i. 13. Halleri Physiolog. T. 3. p. 318.
and T. 8). In the stomach of a calf the quantity of this liquid amounted
to about three pints, and the hairs amongst it were of the same colour
with those on its skin, (Blasii Anat. Animal, p.m. 122). These facts are
attested by many other writers of credit, besides those above
mentioned.

III. It has been deemed a surprising instance
of instinct, that calves and chickens should be able to walk by a few
efforts almost immediately after their nativity: whilst the human infant
in those countries where he is not incumbered with clothes, as in India,
is five or six months, and in our climate almost a twelvemonth, before he
can safely stand upon his feet.

The struggles of all animals in the womb must resemble their mode of
swimming, as by this kind of motion they can best change their attitude
in water. But the swimming of the calf and chicken resembles their manner
of walking, which they have thus in part acquired before their nativity,
and hence accomplish it afterwards with very few efforts, whilst the
swimming of the human creature resembles that of the frog, and totally
differs from his mode of walking.

There is another circumstance to be attended to in this affair, that
not only the growth of those peculiar parts of animals, which are first
wanted to secure their subsistence, are in general furthest advanced
before their nativity: but some animals come into the world more
completely formed throughout their whole system than others: and are
thence much forwarder in all their habits of motion. Thus the colt, and
the lamb, are much more perfect animals than the blind puppy, and the
naked rabbit; and the chick of the pheasant, and the partridge, has more
perfect plumage, and more perfect eyes, as well as greater aptitude to
locomotion, than the callow nestlings of the dove, and of the wren. The
parents of the former only find it necessary to shew them their food, and
to teach them to take it up; whilst those of the latter are obliged for
many days to obtrude it into their gaping mouths.

IV. From the facts mentioned in No. 2. of this Section, it is evinced that the
fœtus learns to swallow before its nativity; for it is seen to open
its mouth, and its stomach is found filled with the liquid that surrounds
it. It opens its mouth, either instigated by hunger, or by the
irksomeness of a continued attitude of the muscles of its face; the
liquor amnii, in which it swims, is agreeable to its palate, as it
consists of a nourishing material, (Haller Phys. T. 8. p. 204). It is
tempted to experience its taste further in the mouth, and by a few
efforts learns to swallow, in the same manner as we learn all other
animal actions, which are attended with consciousness, by the repeated
efforts of our muscles under the conduct of our sensations or
volitions.

The inspiration of air into the lungs is so totally different from
that of swallowing a fluid in which we are immersed, that it cannot be
acquired before our nativity. But at this time, when the circulation of
the blood is no longer continued through the placenta, that suffocating
sensation, which we feel about the precordia, when we are in want of
fresh air, disagreeably affects the infant: and all the muscles of the
body are excited into action to relieve this oppression; those of the
breast, ribs, and diaphragm are found to answer this purpose, and thus
respiration is discovered, and is continued throughout our lives, as
often as the oppression begins to recur. Many infants, both of the human
creature, and of quadrupeds, struggle for a minute after they are born
before they begin to breathe, (Haller Phys. T. 8. p. 400. ib pt. 2. p.
1). Mr. Buffon thinks the action of the dry air upon the nerves of smell
of new-born animals, by producing an endeavour to sneeze, may contribute
to induce this first inspiration, and that the rarefaction of the air by
the warmth of the lungs contributes to induce expiration, (Hist. Nat.
Tom. 4. p. 174). Which latter it may effect by producing a disagreeable
sensation by its delay, and a consequent effort to relieve it. Many
children sneeze before they respire, but not all, as far as I have
observed, or can learn from others.

At length, by the direction of its sense of smell, or by the officious
care of its mother, the young animal approaches the odoriferous rill of
its future nourishment, already experienced to swallow. But in the act of
swallowing, it is necessary nearly to close the mouth, whether the
creature be immersed in the fluid it is about to drink, or not: hence,
when the child first attempts to suck, it does not slightly compress the
nipple between its lips, and suck as an adult person would do, by
absorbing the milk; but it takes the whole nipple into its mouth for this
purpose, compresses it between its gums, and thus repeatedly chewing (as
it were) the nipple, presses out the milk, exactly in the same manner as
it is drawn from the teats of cows by the hands of the milkmaid. The
celebrated Harvey observes, that the fœtus in the womb must have
sucked in a part of its nourishment, because it knows how to suck the
minute it is born, as any one may experience by putting a finger between
its lips, and because in a few days it forgets this art of sucking, and
cannot without some difficulty again acquire it, (Exercit. de Gener.
Anim. 48). The same observation is made by Hippocrates.

A little further experience teaches the young animal to suck by
absorption, as well as by compression; that is, to open the chest as in
the beginning of respiration, and thus to rarefy the air in the mouth,
that the pressure of the denser external atmosphere may contribute to
force out the milk.

The chick yet in the shell has learnt to drink by swallowing a part of
the white of the egg for its food; but not having experienced how to take
up and swallow solid seeds, or grains, is either taught by the felicitous
industry of its mother; or by many repeated attempts is enabled at length
to distinguish and to swallow this kind of nutriment.

And puppies, though they know how to suck like other animals from
their previous experience in swallowing, and in respiration; yet are they
long in acquiring the art of lapping with their tongues, which from the
flaccidity of their cheeks, and length of their mouths, is afterwards a
more convenient way for them to take in water.

V. The senses of smell and taste in many
other animals greatly excel those of mankind, for in civilized society,
as our victuals are generally prepared by others, and are adulterated
with salt, spice, oil, and empyreuma, we do not hesitate about eating
whatever is set before us, and neglect to cultivate these senses: whereas
other animals try every morsel by the smell, before they take it into
their mouths, and by the taste before they swallow it: and are led not
only each to his proper nourishment by this organ of sense, but it also
at a maturer age directs them in the gratification of their appetite of
love. Which may be further understood by considering the sympathies of
these parts described in Class IV. 2. 1. 7. While the human animal is
directed to the object of his love by his sense of beauty, as mentioned
in No. VI. of this Section. Thus Virgil. Georg.
III. 250.

The following curious experiment is related by Galen. “On dissecting a
goat great with young I found a brisk embryon, and having detached it
from the matrix, and snatching it away before it saw its dam, I brought
it into a certain room, where there were many vessels, some filled with
wine, others with oil, some with honey, others with milk, or some other
liquor; and in others were grains and fruits; we first observed the young
animal get upon its feet, and walk; then it shook itself, and afterwards
scratched its side with one of its feet: then we saw it smelling to every
one of these things, that were set in the room; and when it had smelt to
them all, it drank up the milk.” L. 6. de locis. cap. 6.

Parturient quadrupeds, as cats, and bitches, and sows, are led by
their sense of smell to eat the placenta as other common food; why then
do they not devour their whole progeny, as is represented in an antient
emblem of TIME? This is said sometimes to happen
in the unnatural state in which we confine sows; and indeed nature would
seem to have endangered her offspring in this nice circumstance! But at
this time the stimulus of the milk in the tumid teats of the mother
excites her to look out for, and to desire some unknown circumstance to
relieve her. At the same time the smell of the milk attracts the
exertions of the young animals towards its source, and thus the delighted
mother discovers a new appetite, as mentioned in Sect. XIV. 8. and her little progeny are led to receive
and to communicate pleasure by this most beautiful contrivance.

VI. But though the human species in some of
their sensations are much inferior to other animals, yet the accuracy of
the sense of touch, which they possess in so eminent a degree, gives them
a great superiority of understanding; as is well observed by the
ingenious Mr. Buffon. The extremities of other animals terminate in
horns, and hoofs, and claws, very unfit for the sensation of touch;
whilst the human hand is finely adapted to encompass its object with this
organ of sense.

The elephant is indeed endued with a fine sense of feeling at the
extremity of his proboscis, and hence has acquired much more accurate
ideas of touch and of sight than most other creatures. The two following
instances of the sagacity of these animals may entertain the reader, as
they were told me by some gentlemen of distinct observation, and
undoubted veracity, who had been much conversant with our eastern
settlements. First, the elephants that are used to carry the baggage of
our armies, are put each under the care of one of the natives of
Indostan, and whilst himself and his wife go into the woods to collect
leaves and branches of trees for his food, they fix him to the ground by
a length of chain, and frequently leave a child yet unable to walk, under
his protection: and the intelligent animal not only defends it, but as it
creeps about, when it arrives near the extremity of his chain, he wraps
his trunk gently round its body, and brings it again into the centre of
his circle. Secondly, the traitor elephants are taught to walk on a
narrow path between two pit-falls, which are covered with turf, and then
to go into the woods, and to seduce the wild elephants to come that way,
who fall into these wells, whilst he passes safe between them: and it is
universally observed, that those wild elephants that escape the snare,
pursue the traitor with the utmost vehemence, and if they can overtake
him, which sometimes happens, they always beat him to death.

The monkey has a hand well enough adapted for the sense of touch,
which contributes to his great facility of imitation; but in taking
objects with his hands, as a stick or an apple, he puts his thumb on the
same side of them with his fingers, instead of counteracting the pressure
of his fingers with it: from this neglect he is much slower in acquiring
the figures of objects, as he is less able to determine the distances or
diameters of their parts, or to distinguish their vis inertiæ from their
hardness. Helvetius adds, that the shortness of his life, his being
fugitive before mankind, and his not inhabiting all climates, combine to
prevent his improvement. (De l’Esprit. T. 1. p.) There is however at this
time an old monkey shewn in Exeter Change, London, who having lost his
teeth, when nuts are given him, takes a stone into his hand, and cracks
them with it one by one; thus using tools to effect his purpose like
mankind.

The beaver is another animal that makes much use of his hands, and if
we may credit the reports of travellers, is possessed of amazing
ingenuity. This however, M. Buffon affirms, is only where they exist in
large numbers, and in countries thinly peopled with men; while in France
in their solitary state they shew no uncommon ingenuity.

Indeed all the quadrupeds, that have collar-bones, (claviculæ) use
their fore-limbs in some measure as we use our hands, as the cat,
squirrel, tyger, bear and lion; and as they exercise the sense of touch
more universally than other animals, so are they more sagacious in
watching and surprising their prey. All those birds, that use their claws
for hands, as the hawk, parrot, and cuckoo, appear to be more docile and
intelligent; though the gregarious tribes of birds have more acquired
knowledge.

Now as the images, that are painted on the retina of the eye, are no
other than signs, which recall to our imaginations the objects we had
before examined by the organ of touch, as is fully demonstrated by Dr.
Berkley in his treatise on vision; it follows that the human creature has
greatly more accurate and distinct sense of vision than that of any other
animal. Whence as he advances to maturity he gradually acquires a sense
of female beauty, which at this time directs him to the object of his new
passion.

Sentimental love, as distinguished from the animal passion of that
name, with which it is frequently accompanied, consists in the desire or
sensation of beholding, embracing, and saluting a beautiful object.

The characteristic of beauty therefore is that it is the object of
love; and though many other objects are in common language called
beautiful, yet they are only called so metaphorically, and ought to be
termed agreeable. A Grecian temple may give us the pleasurable idea of
sublimity, a Gothic temple may give us the pleasurable idea of variety,
and a modern house the pleasurable idea of utility; music and poetry may
inspire our love by association of ideas; but none of these, except
metaphorically, can be termed beautiful; as we have no wish to embrace or
salute them.

Our perception of beauty consists in our recognition by the sense of
vision of those objects, first, which have before inspired our love by
the pleasure, which they have afforded to many of our senses: as to our
sense of warmth, of touch, of smell, of taste, hunger and thirst; and,
secondly, which bear any analogy of form to such objects.

When the babe, soon after it is born into this cold world, is applied
to its mother’s bosom; its sense of perceiving warmth is first agreeably
affected; next its sense of smell is delighted with the odour of her
milk; then its taste is gratified by the flavour of it: afterwards the
appetites of hunger and of thirst afford pleasure by the possession of
their objects, and by the subsequent digestion of the aliment; and,
lastly, the sense of touch is delighted by the softness and smoothness of
the milky fountain, the source of such variety of happiness.

All these various kinds of pleasure at length become associated with
the form of the mother’s breast; which the infant embraces with its
hands, presses with its lips, and watches with its eyes; and thus
acquires more accurate ideas of the form of its mother’s bosom, than of
the odour and flavour or warmth, which it perceives by its other senses.
And hence at our maturer years, when any object of vision is presented to
us, which by its waving or spiral lines bears any similitude to the form
of the female bosom, whether it be found in a landscape with soft
gradations of rising and descending surface, or in the forms of some
antique vases, or in other works of the pencil or the chissel, we feel a
general glow of delight, which seems to influence all our senses; and, if
the object be not too large, we experience an attraction to embrace it
with our arms, and to salute it with our lips, as we did in our early
infancy the bosom of our mother. And thus we find, according to the
ingenious idea of Hogarth, that the waving lines of beauty were
originally taken from the temple of Venus.

This animal attraction is love; which is a sensation, when the object
is present; and a desire, when it is absent. Which constitutes the purest
source of human felicity, the cordial drop in the otherwise vapid cup of
life, and which overpays mankind for the care and labour, which are
attached to the pre-eminence of his situation above other animals.

It should have been observed, that colour as well as form sometimes
enters into our idea of a beautiful object, as a good complexion for
instance, because a fine or fair colour is in general a sign of health,
and conveys to us an idea of the warmth of the object; and a pale
countenance on the contrary gives an idea of its being cold to the
touch.

It was before remarked, that young animals use their lips to
distinguish the forms of things, as well as their fingers, and hence we
learn the origin of our inclination to salute beautiful objects with our
lips. For a definition of Grace, see Class III. 1. 2. 4.

VII. There are two ways by which we become
acquainted with the passions of others: first, by having observed the
effects of them, as of fear or anger, on our own bodies, we know at sight
when others are under the influence of these affections. So when two
cocks are preparing to fight, each feels the feathers rise round his own
neck, and knows from the same sign the disposition of his adversary: and
children long before they can speak, or understand the language of their
parents, may be frightened by an angry countenance, or soothed by smiles
and blandishments.

Secondly, when we put ourselves into the attitude that any passion
naturally occasions, we soon in some degree acquire that passion; hence
when those that scold indulge themselves in loud oaths, and violent
actions of the arms, they increase their anger by the mode of expressing
themselves: and on the contrary the counterfeited smile of pleasure in
disagreeable company soon brings along with it a portion of the reality,
as is well illustrated by Mr. Burke. (Essay on the Sublime and
Beautiful.)

This latter method of entering into the passions of others is rendered
of very extensive use by the pleasure we take in imitation, which is
every day presented before our eyes, in the actions of children, and
indeed in all the customs and fashions of the world. From this our
aptitude to imitation, arises what is generally understood by the word
sympathy so well explained by Dr. Smith of Glasgow. Thus the appearance
of a cheerful countenance gives us pleasure, and of a melancholy one
makes us sorrowful. Yawning and sometimes vomiting are thus propagated by
sympathy, and some people of delicate fibres, at the presence of a
spectacle of misery, have felt pain in the same parts of their own
bodies, that were diseased or mangled in the other. Amongst the writers
of antiquity Aristotle thought this aptitude to imitation an essential
property of the human species, and calls man an imitative animal. Το
ζωον
μιμωμενον.

These then are the natural signs by which we understand each other,
and on this slender basis is built all human language. For without some
natural signs, no artificial ones could have been invented or understood,
as is very ingeniously observed by Dr. Reid. (Inquiry into the Human
Mind.)

VIII. The origin of this universal language
is a subject of the highest curiosity, the knowledge of which has always
been thought utterly inaccessible. A part of which we shall however here
attempt.

Light, sound, and odours, are unknown to the fœtus in the womb,
which, except the few sensations and motions already mentioned, sleeps
away its time insensible of the busy world. But the moment he arrives
into day, he begins to experience many vivid pains and pleasures; these
are at the same time attended with certain muscular motions, and from
this their early, and individual association, they acquire habits of
occurring together, that are afterwards indissoluble.

1. Of Fear.

As soon as the young animal is born, the first important sensations,
that occur to him, are occasioned by the oppression about his precordia
for want of respiration, and by his sudden transition from ninety-eight
degrees of heat into so cold a climate.—He trembles, that is, he
exerts alternately all the muscles of his body, to enfranchise himself
from the oppression about his bosom, and begins to breathe with frequent
and short respirations; at the same time the cold contracts his red skin,
gradually turning it pale; the contents of the bladder and of the bowels
are evacuated: and from the experience of these first disagreeable
sensations the passion of fear is excited, which is no other than the
expectation of disagreeable sensations. This early association of motions
and sensations persists throughout life; the passion of fear produces a
cold and pale skin, with tremblings, quick respiration, and an evacuation
of the bladder and bowels, and thus constitutes the natural or universal
language of this passion.

On observing a Canary bird this morning, January 28, 1772, at the
house of Mr. Harvey, near Tutbury, in Derbyshire, I was told it always
fainted away, when its cage was cleaned, and desired to see the
experiment. The cage being taken from the ceiling, and its bottom drawn
out, the bird began to tremble, and turned quite white about the root of
his bill: he then opened his mouth as if for breath, and respired quick,
stood straighter up on his perch, hung his wings, spread his tail, closed
his eyes, and appeared quite stiff and cataleptic for near half an hour,
and at length with much trembling and deep respirations came gradually to
himself.

2. Of Grief.

That the internal membrane of the nostrils may be kept always moist,
for the better perception of odours, there are two canals, that conduct
the tears after they have done their office in moistening and cleaning
the ball of the eye into a sack, which is called the lacrymal sack; and
from which there is a duct, that opens into the nostrils: the aperture of
this duct is formed of exquisite sensibility, and when it is stimulated
by odorous particles, or by the dryness or coldness of the air, the sack
contracts itself, and pours more of its contained moisture on the organ
of smell. By this contrivance the organ is rendered more fit for
perceiving such odours, and is preserved from being injured by those that
are more strong or corrosive. Many other receptacles of peculiar fluids
disgorge their contents, when the ends of their ducts are stimulated; as
the gall bladder, when the contents of the duodenum stimulate the
extremity of the common bile duct: and the salivary glands, when the
termination of their ducts in the mouth are excited by the stimulus of
the food we masticate. Atque vesiculæ seminales suum exprimunt fluidum
glande penis fricatâ.

The coldness and dryness of the atmosphere, compared with the warmth
and moisture, which the new-born infant had just before experienced,
disagreeably affects the aperture of this lacrymal sack: the tears, that
are contained in this sack, are poured into the nostrils, and a further
supply is secreted by the lacrymal glands, and diffused upon the
eye-balls; as is very visible in the eyes and nostrils of children soon
after their nativity. The same happens to us at our maturer age, for in
severe frosty weather, snivelling and tears are produced by the coldness
and dryness of the air.

But the lacrymal glands, which separate the tears from the blood, are
situated on the upper external part of the globes of each eye; and, when
a greater quantity of tears are wanted, we contract the forehead, and
bring down the eye-brows, and use many other distortions of the face, to
compress these glands.

Now as the suffocating sensation, that produces respiration, is
removed almost as soon as perceived, and does not recur again: this
disagreeable irritation of the lacrymal ducts, as it must frequently
recur, till the tender organ becomes used to variety of odours, is one of
the first pains that is repeatedly attended to: and hence throughout our
infancy, and in many people throughout their lives, all disagreeable
sensations are attended with snivelling at the nose, a profusion of
tears, and some peculiar distortions of countenance: according to the
laws of early association before mentioned, which constitutes the natural
or universal language of grief.

You may assure yourself of the truth of this observation, if you will
attend to what passes, when you read a distressful tale alone; before the
tears overflow your eyes, you will invariably feel a titillation at that
extremity of the lacrymal duct, which terminates in the nostril, then the
compression of the eyes succeeds, and the profusion of tears.

Linnæus asserts, that the female bear sheds tears in grief; the same
has been said of the hind, and some other animals.

3. Of Tender Pleasure.

The first most lively impression of pleasure, that the infant enjoys
after its nativity, is excited by the odour of its mother’s milk. The
organ of smell is irritated by this perfume, and the lacrymal sack
empties itself into the nostrils, as before explained, and an increase of
tears is poured into the eyes. Any one may observe this, when very young
infants are about to suck; for at those early periods of life, the
sensation affects the organ of smell, much more powerfully, than after
the repeated habits of smelling has inured it to odours of common
strength: and in our adult years, the stronger smells, though they are at
the same time agreeable to us, as of volatile spirits, continue to
produce an increased secretion of tears.

This pleasing sensation of smell is followed by the early affection of
the infant to the mother that suckles it, and hence the tender feelings
of gratitude and love, as well as of hopeless grief, are ever after
joined with the titillation of the extremity of the lacrymal ducts, and a
profusion of tears.

Nor is it singular, that the lacrymal sack should be influenced by
pleasing ideas, as the sight of agreeable food produces the same effect
on the salivary glands. Ac dum vidimus insomniis lascivæ puellæ
simulacrum tenditur penis.

Lambs shake or wriggle their tails, at the time when they first suck,
to get free of the hard excrement, which had been long lodged in their
bowels. Hence this becomes afterwards a mark of pleasure in them, and in
dogs, and other tailed animals. But cats gently extend and contract their
paws when they are pleased, and purr by drawing in their breath, both
which resemble their manner of sucking, and thus become their language of
pleasure, for these animals having collar-bones use their paws like hands
when they suck, which dogs and sheep do not.

4. Of Serene Pleasure.

In the action of sucking, the lips of the infant are closed around the
nipple of its mother, till he has filled his stomach, and the pleasure
occasioned by the stimulus of this grateful food succeeds. Then the
sphincter of the mouth, fatigued by the continued action of sucking, is
relaxed; and the antagonist muscles of the face gently acting, produce
the smile of pleasure: as cannot but be seen by all who are conversant
with children.

Hence this smile during our lives is associated with gentle pleasure;
it is visible in kittens, and puppies, when they are played with, and
tickled; but more particularly marks the human features. For in children
this expression of pleasure is much encouraged, by their imitation of
their parents, or friends; who generally address them with a smiling
countenance: and hence some nations are more remarkable for the gaiety,
and others for the gravity of their looks.

5. Of Anger.

The actions that constitute the mode of fighting, are the immediate
language of anger in all animals; and a preparation for these actions is
the natural language of threatening. Hence the human creature clenches
his fist, and sternly surveys his adversary, as if meditating where to
make the attack; the ram, and the bull, draws himself some steps
backwards, and levels his horns; and the horse, as he most frequently
fights by striking with his hinder feet, turns his heels to his foe, and
bends back his ears, to listen out the place of his adversary, that the
threatened blow may not be ineffectual.

6. Of Attention.

The eye takes in at once but half our horizon, and that only in the
day, and our smell informs us of no very distant objects, hence we
confide principally in the organ of hearing to apprize us of danger: when
we hear any the smallest sound, that we cannot immediately account for,
our fears are alarmed, we suspend our steps, hold every muscle still,
open our mouths a little, erect our ears, and listen to gain further
information: and this by habit becomes the general language of attention
to objects of sight, as well as of hearing; and even to the successive
trains of our ideas.

The natural language of violent pain, which is expressed by writhing
the body, grinning, and screaming; and that of tumultuous pleasure,
expressed in loud laughter; belong to Section XXXIV. on Diseases from Volition.

IX. It must have already appeared to the
reader, that all other animals, as well as man, are possessed of this
natural language of the passions, expressed in signs or tones; and we
shall endeavour to evince, that those animals, which have preserved
themselves from being enslaved by mankind, and are associated in flocks,
are also possessed of some artificial language, and of some traditional
knowledge.

The mother-turkey, when she eyes a kite hovering high in air, has
either seen her own parents thrown into fear at his presence, or has by
observation been acquainted with his dangerous designs upon her young.
She becomes agitated with fear, and uses the natural language of that
passion, her young ones catch the fear by imitation, and in an instant
conceal themselves in the grass.

At the same time that she shews her fears by her gesture and
deportment, she uses a certain exclamation, Koe-ut, Koe-ut, and the young
ones afterwards know, when they hear this note, though they do not see
their dam, that the presence of their adversary is denounced, and hide
themselves as before.

The wild tribes of birds have very frequent opportunities of knowing
their enemies, by observing the destruction they make among their
progeny, of which every year but a small part escapes to maturity: but to
our domestic birds these opportunities so rarely occur, that their
knowledge of their distant enemies must frequently be delivered by
tradition in the manner above explained, through many generations.

This note of danger, as well as the other notes of the mother-turkey,
when she calls her flock to their food, or to sleep under her wings,
appears to be an artificial language, both as expressed by the mother,
and as understood by the progeny. For a hen teaches this language with
equal ease to the ducklings, she has hatched from suppositious eggs, and
educates as her own offspring: and the wagtails, or hedge-sparrows, learn
it from the young cuckoo their softer nursling, and supply him with food
long after he can fly about, whenever they hear his cuckooing, which
Linnæus tells us, is his call of hunger, (Syst. Nat.) And all our
domestic animals are readily taught to come to us for food, when we use
one tone of voice, and to fly from our anger, when we use another.

Rabbits, as they cannot easily articulate sounds, and are formed into
societies, that live under ground, have a very different method of giving
alarm. When danger is threatened, they thump on the ground with one of
their hinder feet, and produce a sound, that can be heard a great way by
animals near the surface of the earth, which would seem to be an
artificial sign both from its singularity and its aptness to the
situation of the animal.

The rabbits on the island of Sor, near Senegal, have white flesh, and
are well tasted, but do not burrow in the earth, so that we may suspect
their digging themselves houses in this cold climate is an acquired art,
as well as their note of alarm, (Adanson’s Voyage to Senegal).

The barking of dogs is another curious note of alarm, and would seem
to be an acquired language, rather than a natural sign: for “in the
island of Juan Fernandes, the dogs did not attempt to bark, till some
European dogs were put among them, and then they gradually begun to
imitate them, but in a strange manner at first, as if they were learning
a thing that was not natural to them,” (Voyage to South America by Don G.
Juan, and Don Ant. de Ulloa. B. 2. c. 4).

Linnæus also observes, that the dogs of South America do not bark at
strangers, (Syst. Nat.) And the European dogs, that have been carried to
Guinea, are said in three or four generations to cease to bark, and only
howl, like the dogs that are natives of that coast, (World Displayed,
Vol. XVII. p. 26.)

A circumstance not dissimilar to this, and equally curious, is
mentioned by Kircherus, de Musurgia, in his Chapter de Lusciniis, “That
the young nightingales, that are hatched under other birds, never sing
till they are instructed by the company of other nightingales.” And
Jonston affirms, that the nightingales that visit Scotland, have not the
same harmony as those of Italy, (Pennant’s Zoology, octavo, p. 255);
which would lead us to suspect that the singing of birds, like human
music, is an artificial language rather than a natural expression of
passion.

X. Our music like our language, is perhaps
entirely constituted of artificial tones, which by habit suggest certain
agreeable passions. For the same combination of notes and tones do not
excite devotion, love, or poetic melancholy in a native of Indostan and
of Europe. And “the Highlander has the same warlike ideas annexed to the
sound of a bagpipe (an instrument which an Englishman derides), as the
Englishman has to that of a trumpet or fife,” (Dr. Brown’s Union of
Poetry and Music, p. 58.) So “the music of the Turks is very different
from the Italian, and the people of Fez and Morocco have again a
different kind, which to us appears very rough and horrid, but is highly
pleasing to them,” (L’Arte Armoniaca a Giorgio Antoniotto). Hence we see
why the Italian opera does not delight an untutored Englishman; and why
those, who are unaccustomed to music, are more pleased with a tune, the
second or third time they hear it, than the first. For then the same
melodious train of sounds excites the melancholy, they had learned from
the song; or the same vivid combination of them recalls all the mirthful
ideas of the dance and company.

Even the sounds, that were once disagreeable to us, may by habit be
associated with other ideas, so as to become agreeable. Father Lasitau,
in his account of the Iroquois, says “the music and dance of those
Americans, have something in them extremely barbarous, which at first
disgusts. We grow reconciled to them by degrees, and in the end partake
of them with pleasure, the savages themselves are fond of them to
distraction,” (Mœurs des Savages, Tom. ii.)

There are indeed a few sounds, that we very generally associate with
agreeable ideas, as the whistling of birds, or purring of animals, that
are delighted; and some others, that we as generally associate with
disagreeable ideas, as the cries of animals in pain, the hiss of some of
them in anger, and the midnight howl of beasts of prey. Yet we receive no
terrible or sublime ideas from the lowing of a cow, or the braying of an
ass. Which evinces, that these emotions are owing to previous
associations. So if the rumbling of a carriage in the street be for a
moment mistaken for thunder, we receive a sublime sensation, which ceases
as soon as we know it is the noise of a coach and six.

There are other disagreeable sounds, that are said to set the teeth on
edge; which, as they have always been thought a necessary effect of
certain discordant notes, become a proper subject of our enquiry. Every
one in his childhood has repeatedly bit a part of the glass or earthen
vessel, in which his food has been given him, and has thence had a very
disagreeable sensation in the teeth, which sensation was designed by
nature to prevent us from exerting them on objects harder than
themselves. The jarring sound produced between the cup and the teeth is
always attendant on this disagreeable sensation: and ever after when such
a sound is accidentally produced by the conflict of two hard bodies, we
feel by association of ideas the concomitant disagreeable sensation in
our teeth.

Others have in their infancy frequently held the corner of a silk
handkerchief in their mouth, or the end of the velvet cape of their coat,
whilst their companions in play have plucked it from them, and have given
another disagreeable sensation to their teeth, which has afterwards
recurred on touching those materials. And the sight of a knife drawn
along a china plate, though no sound is excited by it, and even the
imagination of such a knife and plate so scraped together, I know by
repeated experience will produce the same disagreeable sensation of the
teeth.

These circumstances indisputably prove, that this sensation of the
tooth-edge is owing to associated ideas; as it is equally excitable by
sight, touch, hearing, or imagination.

In respect to the artificial proportions of sound excited by musical
instruments, those, who have early in life associated them with agreeable
ideas, and have nicely attended to distinguish them from each other, are
said to have a good ear, in that country where such proportions are in
fashion: and not from any superior perfection in the organ of hearing, or
any intuitive sympathy between certain sounds and passions.

I have observed a child to be exquisitely delighted with music, and
who could with great facility learn to sing any tune that he heard
distinctly, and yet whole organ of hearing was so imperfect, that it was
necessary to speak louder to him in common conversation than to
others.

Our music, like our architecture, seems to have no foundation in
nature, they are both arts purely of human creation, as they imitate
nothing. And the professors of them have only classed those
circumstances, that are most agreeable to the accidental taste of their
age, or country; and have called it Proportion. But this proportion must
always fluctuate, as it rests on the caprices, that are introduced into
our minds by our various modes of education. And these fluctuations of
taste must become more frequent in the present age, where mankind have
enfranchised themselves from the blind obedience to the rules of
antiquity in perhaps every science, but that of architecture. See Sect.
XII. 7. 3.

XI. There are many articles of knowledge,
which the animals in cultivated countries seem to learn very early in
their lives, either from each other, or from experience, or observation:
one of the most general of these is to avoid mankind. There is so great a
resemblance in the natural language of the passions of all animals, that
we generally know, when they are in a pacific, or in a malevolent humour,
they have the same knowledge of us; and hence we can scold them from us
by some tones and gestures, and could possibly attract them to us by
others, if they were not already apprized of our general malevolence
towards them. Mr. Gmelin, Professor at Petersburg, assures us, that in
his journey into Siberia, undertaken by order of the Empress of Russia,
he saw foxes, that expressed no fear of himself or companions, but
permitted him to come quite near them, having never seen the human
creature before. And Mr. Bongainville relates, that at his arrival at the
Malouine, or Falkland’s Islands, which were not inhabited by men, all the
animals came about himself and his people; the fowls settling upon their
heads and shoulders, and the quadrupeds running about their feet. From
the difficulty of acquiring the confidence of old animals, and the ease
of taming young ones, it appears that the fear, they all conceive at the
sight of mankind, is an acquired article of knowledge.

This knowledge is more nicely understood by rooks, who are formed into
societies, and build, as it were, cities over our heads; they evidently
distinguish, that the danger is greater when a man is armed with a gun.
Every one has seen this, who in the spring of the year has walked under a
rookery with a gun in his hand: the inhabitants of the trees rise on
their wings, and scream to the unfledged young to shrink into their nests
from the sight of the enemy. The vulgar observing this circumstance so
uniformly to occur, assert that rooks can smell gun-powder.

The fieldfares, (turdus pilarus) which breed in Norway, and come
hither in the cold season for our winter berries; as they are associated
in flocks, and are in a foreign country, have evident marks of keeping a
kind of watch, to remark and announce the appearance of danger. On
approaching a tree, that is covered with them, they continue fearless
till one at the extremity of the bush rising on his wings gives a loud
and peculiar note of alarm, when they all immediately fly, except one
other, who continues till you approach still nearer, to certify as it
were the reality of the danger, and then he also flies off repeating the
note of alarm.

And in the woods about Senegal there is a bird called uett-uett by the
negroes, and squallers by the French, which, as soon as they see a man,
set up a loud scream, and keep flying round him, as if their intent was
to warn other birds, which upon hearing the cry immediately take wing.
These birds are the bane of sportsmen, and frequently put me into a
passion, and obliged me to shoot them, (Adanson’s Voyage to Senegal, 78).
For the same intent the lesser birds of our climate seem to fly after a
hawk, cuckoo, or owl, and scream to prevent their companions from being
surprised by the general enemies of themselves, or of their eggs and
progeny.

But the lapwing, (charadrius pluvialis Lin.) when her unfledged
offspring run about the marshes, where they were hatched, not only gives
the note of alarm at the approach of men or dogs, that her young may
conceal themselves; but flying and screaming near the adversary, she
appears more felicitous and impatient, as he recedes from her family, and
thus endeavours to mislead him, and frequently succeeds in her design.
These last instances are so apposite to the situation, rather than to the
natures of the creatures, that use them; and are so similar to the
actions of men in the same circumstances, that we cannot but believe,
that they proceed from a similar principle.

Miss M.E. Jacson acquainted me, that she witnessed this autumn an
agreeable instance of sagacity in a little bird, which seemed to use the
means to obtain an end; the bird repeatedly hopped upon a poppy-stem, and
shook the head with its bill, till many seeds were scattered, then it
settled on the ground, and eat the seeds, and again repeated the same
management. Sept. 1, 1794.

On the northern coast of Ireland a friend of mine saw above a hundred
crows at once preying upon muscles; each crow took a muscle up into the
air twenty or forty yards high, and let it fall on the stones, and thus
by breaking the shell, got possession of the animal.—A certain
philosopher (I think it was Anaxagoras) walking along the sea-shore to
gather shells, one of these unlucky birds mistaking his bald head for a
stone, dropped a shell-fish upon it, and killed at once a philosopher and
an oyster.

Our domestic animals, that have some liberty, are also possessed of
some peculiar traditional knowledge: dogs and cats have been forced into
each other’s society, though naturally animals of a very different kind,
and have hence learned from each other to eat dog’s grass (agrostis
canina) when they are sick, to promote vomiting. I have seen a cat
mistake the blade of barley for this grass, which evinces it is an
acquired knowledge. They have also learnt of each other to cover their
excrement and urine;—about a spoonful of water was spilt upon my
hearth from the tea-kettle, and I observed a kitten cover it with ashes.
Hence this must also be an acquired art, as the creature mistook the
application of it.

To preserve their fur clean, and especially their whiskers, cats wash
their faces, and generally quite behind their ears, every time they eat.
As they cannot lick those places with their tongues, they first wet the
inside of the leg with saliva, and then repeatedly wash their faces with
it, which must originally be an effect of reasoning, because a means is
used to produce an effect; and seems afterwards to be taught or acquired
by imitation, like the greatest part of human arts.

These animals seem to possess something like an additional sense by
means of their whiskers; which have perhaps some analogy to the antennæ
of moths and butterflies. The whiskers of cats consist not only of the
long hairs on their upper lips, but they have also four or five long
hairs standing up from each eyebrow, and also two or three on each cheek;
all which, when the animal erects them, make with their points so many
parts of the periphery of a circle, of an extent at least equal to the
circumference of any part of their own bodies. With this instrument, I
conceive, by a little experience, they can at once determine, whether any
aperture amongst hedges or shrubs, in which animals of this genus live in
their wild state, is large enough to admit their bodies; which to them is
a matter of the greatest consequence, whether pursuing or pursued. They
have likewise a power of erecting and bringing forward the whiskers on
their lips; which probably is for the purpose of feeling, whether a dark
hole be further permeable.

The antennæ, or horns, of butterflies and moths, who have awkward
wings, the minute feathers of which are very liable to injury, serve, I
suppose, a similar purpose of measuring, as they fly or creep amongst the
leaves of plants and trees, whither their wings can pass without touching
them.

Mr. Leonard, a very intelligent friend of mine, saw a cat catch a
trout by darting upon it in a deep clear water at the mill at Weaford,
near Lichfield. The cat belonged to Mr. Stanley, who had often seen her
catch fish in the same manner in summer, when the mill-pool was drawn so
low, that the fish could be seen. I have heard of other cats taking fish
in shallow water, as they stood on the bank. This seems a natural art of
taking their prey in cats, which their acquired delicacy by domestication
has in general prevented them from using, though their desire of eating
fish continues in its original strength.

Mr. White, in his ingenious History of Selbourn, was witness to a
cat’s suckling a young hare, which followed her about the garden, and
came jumping to her call of affection. At Elford, near Lichfield, the
Rev. Mr. Sawley had taken the young ones out of a hare, which was shot;
they were alive, and the cat, who had just lost her own kittens, carried
them away, as it was supposed, to eat them; but it presently appeared,
that it was affection not hunger which incited her, as she suckled them,
and brought them up as their mother.

Other instances of the mistaken application of what has been termed
instinct may be observed in flies in the night, who mistaking a candle
for day-light, approach and perish in the flame. So the putrid smell of
the stapelia, or carrion-flower, allures the large flesh-fly to deposit
its young worms on its beautiful petals, which perish there for want of
nourishment. This therefore cannot be a necessary instinct, because the
creature mistakes the application of it.

Though in this country horses shew little vestiges of policy, yet in
the deserts of Tartary, and Siberia, when hunted by the Tartars they are
seen to form a kind of community, set watches to prevent their being
surprised, and have commanders, who direct, and hasten their flight,
Origin of Language, Vol. I. p. 212. In this country, where four or five
horses travel in a line, the first always points his ears forward, and
the last points his backward, while the intermediate ones seem quite
careless in this respect; which seems a part of policy to prevent
surprise. As all animals depend most on the ear to apprize them of the
approach of danger, the eye taking in only half the horizon at once, and
horses possess a great nicety of this sense; as appears from their mode
of fighting mentioned No. 8. 5. of this
Section, as well as by common observation.

There are some parts of a horse, which he cannot conveniently rub,
when they itch, as about the shoulder, which he can neither bite with his
teeth, nor scratch with his hind foot; when this part itches, he goes to
another horse, and gently bites him in the part which he wishes to be
bitten, which is immediately done by his intelligent friend. I once
observed a young foal thus bite its large mother, who did not choose to
drop the grass she had in her mouth, and rubbed her nose against the
foal’s neck instead of biting it; which evinces that she knew the design
of her progeny, and was not governed by a necessary instinct to bite
where she was bitten.

Many of our shrubs, which would otherwise afford an agreeable food to
horses, are armed with thorns or prickles, which secure them from those
animals; as the holly, hawthorn, gooseberry, gorse. In the extensive
moorlands of Staffordshire, the horses have learnt to stamp upon a
gorse-bush with one of their fore-feet for a minute together, and when
the points are broken, they eat it without injury. The horses in the new
forest in Hampshire are affirmed to do the same by Mr. Gilpin. Forest
Scenery, II. 251, and 112. Which is an art other horses in the fertile
parts of the country do not possess, and prick their mouths till they
bleed, if they are induced by hunger or caprice to attempt eating
gorse.

Swine have a sense of touch as well as of smell at the end of their
nose, which they use as a hand, both to root up the soil, and to turn
over and examine objects of food, somewhat like the proboscis of an
elephant. As they require shelter from the cold in this climate, they
have learnt to collect straw in their mouths to make their nest, when the
wind blows cold; and to call their companions by repeated cries to assist
in the work, and add to their warmth by their numerous bedfellows. Hence
these animals, which are esteemed so unclean, have also learned never to
befoul their dens, where they have liberty, with their own excrement; an
art, which cows and horses, which have open hovels to run into, have
never acquired. I have observed great sagacity in swine; but the short
lives we allow them, and their general confinement, prevents their
improvement, which might probably be otherwise greater than that of
dogs.

Instances of the sagacity and knowledge of animals are very numerous
to every observer, and their docility in learning various arts from
mankind, evinces that they may learn similar arts from their own species,
and thus be possessed of much acquired and traditional knowledge.

A dog whose natural prey is sheep, is taught by mankind, not only to
leave them unmolested, but to guard them; and to hunt, to set, or to
destroy other kinds of animals, as birds, or vermin; and in some
countries to catch fish, in others to find truffles, and to practise a
great variety of tricks; is it more surprising that the crows should
teach each other, that the hawk can catch less birds, by the superior
swiftness of his wing, and if two of them follow him, till he succeeds in
his design, that they can by force share a part of the capture? This I
have formerly observed with attention and astonishment.

There is one kind of pelican mentioned by Mr. Osbeck, one of Linnæus’s
travelling pupils (the pelicanus aquilus), whose food is fish; and which
it takes from other birds, because it is not formed to catch them itself;
hence it is called by the English a Man-of-war-bird, Voyage to China, p.
88. There are many other interesting anecdotes of the pelican and
cormorant, collected from authors of the best authority, in a
well-managed Natural History for Children, published by Mr. Galton.
Johnson. London.

And the following narration from the very accurate Mons. Adanson, in
his Voyage to Senegal, may gain credit with the reader: as his employment
in this country was solely to make observations in natural history. On
the river Niger, in his road to the island Griel, he saw a great number
of pelicans, or wide throats. “They moved with great state like swans
upon the water, and are the largest bird next to the ostrich; the bill of
the one I killed was upwards of a foot and half long, and the bag
fastened underneath it held two and twenty pints of water. They swim in
flocks, and form a large circle, which they contract afterwards, driving
the fish before them with their legs: when they see the fish in
sufficient number confined in this space, they plunge their bill wide
open into the water, and shut it again with great quickness. They thus
get fish into their throat-bag, which they eat afterwards on shore at
their leisure.” P. 247.

XII. The knowledge and language of those
birds, that frequently change their climate with the seasons, is still
more extensive: as they perform these migrations in large societies, and
are less subject to the power of man, than the resident tribes of birds.
They are said to follow a leader during the day, who is occasionally
changed, and to keep a continual cry during the night to keep themselves
together. It is probable that these emigrations were at first undertaken
as accident directed, by the more adventurous of their species, and
learned from one another like the discoveries of mankind in navigation.
The following circumstances strongly support this opinion.

1. Nature has provided these animals, in
the climates where they are produced, with another resource: when the
season becomes too cold for their constitutions, or the food they were
supported with ceases to be supplied, I mean that of sleeping. Dormice,
snakes, and bats, have not the means of changing their country; the two
former from the want of wings, and the latter from his being not able to
bear the light of the day. Hence these animals are obliged to make use of
this resource, and sleep during the winter. And those swallows that have
been hatched too late in the year to acquire their full strength of
pinion, or that have been maimed by accident or disease, have been
frequently found in the hollows of rocks on the sea coasts, and even
under water in this torpid state, from which they have been revived by
the warmth of a fire. This torpid state of swallows is testified by
innumerable evidences both of antient and modern names. Aristotle
speaking of the swallows says, “They pass into warmer climates in winter,
if such places are at no great distance; if they are, they bury
themselves in the climates where they dwell,” (8. Hist. c. 16. See also
Derham’s Phys. Theol. v. ii. p. 177.)

Hence their emigrations cannot depend on a necessary instinct,
as the emigrations themselves are not necessary.

2. When the weather becomes cold, the
swallows in the neighbourhood assemble in large flocks; that is, the
unexperienced attend those that have before experienced the journey they
are about to undertake: they are then seen some time to hover on the
coast, till there is calm whether, or a wind, that suits the direction of
their flight. Other birds of passage have been drowned by thousands in
the sea, or have settled on ships quite exhausted with fatigue. And
others, either by mistaking their course, or by distress of weather, have
arrived in countries where they were never seen before: and thus are
evidently subject to the same hazards that the human species undergo, in
the execution of their artificial purposes.

3. The same birds are emigrant from some
countries and not so from others: the swallows were seen at Goree in
January by an ingenious philosopher of my acquaintance, and he was told
that they continued there all the year; as the warmth of the climate was
at all seasons sufficient for their own constitutions, and for the
production of the flies that supply them with nourishment. Herodotus
says, that in Libya, about the springs of the Nile, the swallows continue
all the year. (L. 2.)

Quails (tetrao corturnix, Lin.) are birds of passage from the coast of
Barbary to Italy, and have frequently settled in large shoals on ships
fatigued with their flight. (Ray, Wisdom of God, p. 129. Derham. Physic.
Theol. v. ii. p. 178,) Dr. Ruffel, in his History of Aleppo, observes
that the swallows visit that country about the end of February, and
having hatched their young disappear about the end of July; and returning
again about the beginning of October, continue about a fortnight, and
then again disappear. (P. 70.)

When my late friend Dr. Chambres, of Derby, was on the island of
Caprea in the bay of Naples, he was informed that great flights of quails
annually settle on that island about the beginning of May, in their
passage from Africa to Europe. And that they always come when the
south-east wind blows, are fatigued when they rest on this island, and
are taken in such amazing quantities and sold to the Continent, that the
inhabitants pay the bishop his stipend out of the profits arising from
the sale of them.

The flights of these birds across the Mediterranean are recorded near
three thousand years ago. “There went forth a wind from the Lord and
brought quails from the sea, and let them fall upon the camp, a day’s
journey round about it, and they were two cubits above the earth,”
(Numbers, chap. ii. ver. 31.)

In our country, Mr. Pennant informs us, that some quails migrate, and
others only remove from the internal parts of the island to the coasts,
(Zoology, octavo, 210.) Some of the ringdoves and stares breed here,
others migrate, (ibid. 510, ii.) And the slender billed small birds do
not all quit these kingdoms in the winter, though the difficulty of
procuring the worms and insects, that they feed on, supplies the same
reason for migration to them all, (ibid. 511.)

Linnæus has observed, that in Sweden the female chaffinches quit that
country in September, migrating into Holland, and leave their mates
behind till their return in spring. Hence he has called them Fringilla
cælebs, (Amæn. Acad. ii. 42. iv. 595.) Now in our climate both sexes of
them are perennial birds. And Mr. Pennant observes that the hoopoe,
chatterer, hawfinch, and crossbill, migrate into England so rarely, and
at such uncertain times, as not to deserve to be ranked among our birds
of passage, (ibid. 511.)

The water fowl, as geese and ducks, are better adapted for long
migrations, than the other tribes of birds, as, when the weather is calm,
they can not only rest themselves, or sleep upon the ocean, but possibly
procure some kind of food from it.

Hence in Siberia, as soon as the lakes are frozen, the water fowl,
which are very numerous, all disappear, and are supposed to fly to warmer
climates, except the rail, which, from its inability for long flights,
probably sleeps, like our bat, in their winter. The following account
from the Journey of Professor Gmelin, may entertain the reader. “In the
neighbourhood of Krasnoiark, amongst many other emigrant water fowls, we
observed a great number of rails, which when pursued never took flight,
but endeavoured to escape by running. We enquired how these birds, that
could not fly, could retire into other countries in the winter, and were
told, both by the Tartars and Assanians, that they well knew those birds
could not alone pass into other countries: but when the cranes (les
grues) retire in autumn, each one takes a rail (un rale) upon his back,
and carries him to a warmer climate.”

Recapitulation.

1. All birds of passage can exist in the climates, where they are
produced.

2. They are subject in their migrations to the same accidents and
difficulties, that mankind are subject to in navigation.

3. The same species of birds migrate from some countries, and are
resident in others.

From all these circumstances it appears that the migrations of birds
are not produced by a necessary instinct, but are accidental
improvements, like the arts among mankind, taught by their cotemporaries,
or delivered by tradition from one generation of them to another.

XIII. In that season of the year which
supplies the nourishment proper for the expected brood, the birds enter
into a contract of marriage, and with joint labour construct a bed for
the reception of their offspring. Their choice of the proper season,
their contracts of marriage, and the regularity with which they construct
their nests, have in all ages excited the admiration of naturalists; and
have always been attributed to the power of instinct, which, like the
occult qualities of the antient philosophers, prevented all further
enquiry. We shall consider them in their order.

Their Choice of the Season.

Our domestic birds, that are plentifully supplied throughout the year
with their adapted food, and are covered with houses from the inclemency
of the weather, lay their eggs at any season: which evinces that the
spring of the year is not pointed out to them by a necessary
instinct.

Whilst the wild tribes of birds choose this time of the year from
their acquired knowledge, that the mild temperature of the air is more
convenient for hatching their eggs, and is soon likely to supply that
kind of nourishment, that is wanted for their young.

If the genial warmth of the spring produced the passion of love, as it
expands the foliage of trees, all other animals should feel its influence
as well as birds: but, the viviparous creatures, as they suckle their
young, that is, as they previously digest the natural food, that it may
better suit the tender stomachs of their offspring, experience the
influence of this passion at all seasons of the year, as cats and
bitches. The graminivorous animals indeed generally produce their young
about the time when grass is supplied in the greatest plenty, but this is
without any degree of exactness, as appears from our cows, sheep, and
hares, and may be a part of the traditional knowledge, which they learn
from the example of their parents.

Their Contracts of Marriage.

Their mutual passion, and the acquired knowledge, that their joint
labour is necessary to procure sustenance for their numerous family,
induces the wild birds to enter into a contract of marriage, which does
not however take place among the ducks, geese, and fowls, that are
provided with their daily food from our barns.

An ingenious philosopher has lately denied, that animals can enter
into contracts, and thinks this an essential difference between them and
the human creature:—but does not daily observation convince us,
that they form contracts of friendship with each other, and with mankind?
When puppies and kittens play together, is there not a tacit contract,
that they will not hurt each other? And does not your favorite dog expect
you should give him his daily food, for his services and attention to
you? And thus barters his love for your protection? In the same manner
that all contracts are made amongst men, that do not understand each
others arbitrary language.

Construction of their Nests.

1. They seem to be instructed how to build
their nests from their observation of that, in which they were educated,
and from their knowledge of those things, that are most agreeable to
their touch in respect: to warmth, cleanliness, and stability. They
choose their situations from their ideas of safety from their enemies,
and of shelter from the weather. Nor is the colour of their nests a
circumstance unthought of; the finches, that build in green hedges, cover
their habitations with green moss; the swallow or martin, that builds
against rocks and houses, covers her’s with clay, whilst the lark chooses
vegetable straw nearly of the colour of the ground she inhabits: by this
contrivance, they are all less liable to be discovered by their
adversaries.

2. Nor are the nests of the same species
of birds constructed always of the same materials, nor in the same form;
which is another circumstance that ascertains, that they are led by
observation.

In the trees before Mr. Levet’s house in Lichfield, there are annually
nests built by sparrows, a bird which usually builds under the tiles of
houses, or the thatch of barns. Not finding such convenient situations
for their nests, they build a covered nest bigger than a man’s head, with
an opening like a mouth at the side, resembling that of a magpie, except
that it is built with straw and hay, and lined with feathers, and so
nicely managed as to be a defence against both wind and rain.

The following extract from a Letter of the Rev. Mr. J. Darwin, of
Carleton Scroop in Lincolnshire, authenticates a curious fact of this
kind. “When I mentioned to you the circumstance of crows or rooks
building in the spire of Welbourn church, you expressed a desire of being
well informed of the certainty of the fact. Welbourn is situated in the
road from Grantham to Lincoln on the Cliff row; I yesterday took a ride
thither, and enquired of the rector, Mr. Ridgehill, whether the report
was true, that rooks built in the spire of his church. He assured me it
was true, and that they had done so time immemorial, as his parishioners
affirmed. There was a common tradition, he said, that formerly a rookery
in some high trees adjoined the church yard, which being cut down
(probably in the spring, the building season), the rooks removed to the
church, and built their nests on the outside of the spire on the tops of
windows, which by their projection a little from the spire made them
convenient room, but that they built also on the inside. I saw two nests
made with sticks on the outside, and in the spires, and Mr. Ridgehill
said there were always a great many.

“I spent the day with Mr. Wright, a clergyman, at Fulbeck, near
Welbourn, and in the afternoon Dr. Ellis of Headenham, about two miles
from Welbourn, drank tea at Mr. Wright’s, who said he remembered, when
Mr. Welby lived at Welbourn, that he received a letter from an
acquaintance in the west of England, desiring an answer, whether the
report of rooks building in Welbourn church was true, as a wager was
depending on that subject; to which he returned an answer ascertaining
the fact, and decided the wager.” Aug. 30, 1794.

So the jackdaw (corvus monedula) generally builds in church-steeples,
or under the roofs of high houses; but at Selbourn, in Southamptonshire,
where towers and steeples are not sufficiently numerous, these birds
build in forsaken rabbit burrows. See a curious account of these
subterranean nests in White’s History of Selbourn, p. 59. Can the skilful
change of architecture in these birds and the sparrows above mentioned be
governed by instinct? Then they must have two instincts, one for common,
and the other for extraordinary occasions.

I have seen green worsted in a nest, which no where exists in nature:
and the down of thistles in those nests, that were by some accident
constructed later in the summer, which material could not be procured for
the earlier nests: in many different climates they cannot procure the
same materials, that they use in ours. And it is well known, that the
canary birds, that are propagated in this country, and the finches, that
are kept tame, will build their nests of any flexile materials, that are
given them. Plutarch, in his Book on Rivers, speaking of the Nile, says,
“that the swallows collect a material, when the waters recede, with which
they form nests, that are impervious to water.” And in India there is a
swallow that collects a glutinous substance for this purpose, whose nest
is esculent, and esteemed a principal rarity amongst epicures, (Lin.
Syst. Nat.) Both these must be constructed of very different materials
from those used by the swallows of our country.

In India the birds exert more artifice in building their nests on
account of the monkeys and snakes: some form their pensile nests in the
shape of a purse, deep and open at top; others with a hole in the side;
and others, still more cautious, with an entrance at the very bottom,
forming their lodge near the summit. But the taylor-bird will not ever
trust its nest to the extremity of a tender twig, but makes one more
advance to safety by fixing it to the leaf itself. It picks up a dead
leaf, and sews it to the side of a living one, its slender bill being its
needle, and its thread some fine fibres; the lining consists of feathers,
gossamer, and down; its eggs are white, the colour of the bird light
yellow, its length three inches, its weight three sixteenths of an ounce;
so that the materials of the nest, and the weight of the bird, are not
likely to draw down an habitation so slightly suspended. A nest of this
bird is preserved in the British Museum, (Pennant’s Indian Zoology). This
calls to one’s mind the Mosaic account of the origin of mankind, the
first dawning of art there ascribed to them, is that of sewing leaves
together. For many other curious kinds of nests see Natural History for
Children, by Mr. Galton. Johnson. London. Part I. p. 47. Gen.
Oriolus.

3. Those birds that are brought up by our
care, and have had little communication with others of their own species,
are very defective in this acquired knowledge; they are not only very
awkward in the construction of their nests, but generally scatter their
eggs in various parts of the room or cage, where they are confined, and
seldom produce young ones, till, by failing in their first attempt, they
have learnt something from their own observation.

4. During the time of incubation birds are
said in general to turn their eggs every day; some cover them, when they
leave the nest, as ducks and geese; in some the male is said to bring
food to the female, that she may have less occasion of absence, in others
he is said to take her place, when she goes in quest of food; and all of
them are said to leave their eggs a shorter time in cold weather than in
warm. In Senegal the ostrich sits on her eggs only during the night,
leaving them in the day to the heat of the sun; but at the Cape of Good
Hope, where the heat is less, she sits on them day and night.

If it should be asked, what induces a bird to sit weeks on its first
eggs unconscious that a brood of young ones will be the product? The
answer must be, that it is the same passion that induces the human mother
to hold her offspring whole nights and days in her fond arms, and press
it to her bosom, unconscious of its future growth to sense and manhood,
till observation or tradition have informed her.

5. And as many ladies are too refined to
nurse their own children, and deliver them to the care and provision of
others; so is there one instance of this vice in the feathered world. The
cuckoo in some parts of England, as I am well informed by a very distinct
and ingenious gentleman, hatches and educates her own young; whilst in
other parts she builds no nest, but uses that of some lesser bird,
generally either of the wagtail, or hedge sparrow, and depositing one egg
in it, takes no further care of her progeny.

As the Rev. Mr. Stafford was walking in Glosop Dale, in the Peak of
Derbyshire, he saw a cuckoo rise from its nest. The nest was on the stump
of a tree, that had been some time felled, among some chips that were in
part turned grey, so as much to resemble the colour of the bird, in this
nest were two young cuckoos: tying a string about the leg of one of them,
he pegged the other end of it to the ground, and very frequently for many
days beheld the old cuckoo feed these her young, as he stood very near
them.

The following extract of a Letter from the Rev. Mr. Wilmot, of Morley,
near Derby, strengthens the truth of the fact above mentioned, of the
cuckoo sometimes making a nest, and hatching her own young.

“In the beginning of July 1792, I was attending some labourers on my
farm, when one of them said to me, “There is a bird’s nest upon one of
the Coal-slack Hills; the bird is now sitting, and is exactly like a
cuckoo. They say that cuckoo’s never hatch their own eggs, otherwise I
should have sworn it was one.” He took me to the spot, it was in an open
fallow ground; the bird was upon the nest, I stood and observed her some
time, and was perfectly satisfied it was a cuckoo; I then put my hand
towards her, and she almost let me touch her before she rose from the
nest, which she appeared to quit with great uneasiness, skimming over the
ground in the manner that a hen partridge does when disturbed from a new
hatched brood, and went only to a thicket about forty or fifty yards from
the nest; and continued there as long as I staid to observe her, which
was not many minutes. In the nest, which was barely a hole scratched out
of the coal-slack in the manner of a plover’s nest, I observed three
eggs, but did not touch them. As I had labourers constantly at work in
that field, I went thither every day, and always looked to see if the
bird was there, but did not disturb her for seven or eight days, when I
was tempted to drive her from the nest, and found two young ones,
that appeared to have been hatched some days, but there was no appearance
of the third egg. I then mentioned this extraordinary circumstance (for
such I thought it) to Mr. and Mrs. Holyoak of Bidford Grange,
Warwickshire, and to Miss M. Willes, who were on a visit at my house, and
who all went to see it. Very lately I reminded Mr. Holyoak of it, who
told me he had a perfect recollection of the whole, and that, considering
it a curiosity, he walked to look at it several times, was perfectly
satisfied as to its being a cuckoo, and thought her more attentive to her
young, than any other bird he ever observed, having always found her
brooding her young. In about a week after I first saw the young ones, one
of them was missing, and I rather suspected my plough-boys having taken
it; though it might possibly have been taken by a hawk, some time when
the old one was seeking food. I never found her off her nest but once,
and that was the last time I saw the remaining young one, when it was
almost full feathered. I then went from home for two or three days, and,
when I returned, the young one was gone, which I take for granted had
flown. Though during this time I frequently saw cuckoos in the thicket I
mention, I never observed any one, that I supposed to be the cock-bird,
paired with this hen.”

Nor is this a new observation, though it is entirely overlooked by the
modern naturalists, for Aristotle speaking of the cuckoo, asserts that
she sometimes builds her nest among broken rocks, and on high mountains,
(L. 6. H. c. 1.) but adds in another place that she generally possesses
the nest of another bird, (L. 6. H. c. 7.) And Niphus says that cuckoos
rarely build for themselves, most frequently laying their eggs in the
nests of other birds, (Gesner, L. 3. de Cuculo.)

The Philosopher who is acquainted with these facts concerning the
cuckoo, would seem to have very little reason himself, if he could
imagine this neglect of her young to be a necessary instinct!

XIV. The deep recesses of the ocean are
inaccessible to mankind, which prevents us from having much knowledge of
the arts and government of its inhabitants.

1. One of the baits used by the fisherman
is an animal called an Old Soldier, his size and form are somewhat like
the craw-fish, with this difference, that his tail is covered with a
tough membrane instead of a shell; and to obviate this defect, he seeks
out the uninhabited shell of some dead fish, that is large enough to
receive his tail, and carries it about with him as part of his clothing
or armour.

2. On the coasts about Scarborough, where
the haddocks, cods, and dog-fish, are in great abundance, the fishermen
universally believe that the dog-fish make a line, or semicircle, to
encompass a shoal of haddocks and cod, confining them within certain
limits near the shore, and eating them as occasion requires. For the
haddocks and cod are always found near the shore without any dog-fish
among them, and the dog-fish further off without any haddocks or cod; and
yet the former are known to prey upon the latter, and in some years
devour such immense quantities as to render this fishery more expensive
than profitable.

3. The remora, when he wishes to remove
his situation, as he is a very slow swimmer, is content to take an
outside place on whatever conveyance is going his way; nor can the
cunning animal be tempted to quit his hold of a ship when she is sailing,
not even for the lucre of a piece of pork, lest it should endanger the
loss of his passage: at other times he is easily caught with the
hook.

4. The crab-fish, like many other
testaceous animals, annually changes its shell; it is then in a soft
state, covered only with a mucous membrane, and conceals itself in holes
in the sand or under weeds; at this place a hard shelled crab always
stands centinel, to prevent the sea insects from injuring the other in
its defenceless state; and the fishermen from his appearance know where
to find the soft ones, which they use for baits in catching other
fish.

And though the hard shelled crab, when he is on this duty, advances
boldly to meet the foe, and will with difficulty quit the field; yet at
other times he shews great timidity, and has a wonderful speed in
attempting his escape; and, if often interrupted, will pretend death like
the spider, and watch an opportunity to sink himself into the sand,
keeping only his eyes above. My ingenious friend Mr. Burdett, who
favoured me with these accounts at the time he was surveying the coasts,
thinks the commerce between the sexes takes place at this time, and
inspires the courage of the creature.

5. The shoals of herrings, cods, haddocks,
and other fish, which approach our shores at certain seasons, and quit
them at other seasons without leaving one behind; and the salmon, that
periodically frequent our rivers, evince, that there are vagrant tribes
of fish, that perform as regular migrations as the birds of passage
already mentioned.

6. There is a cataract on the river Liffey
in Ireland about nineteen feet high: here in the salmon season many of
the inhabitants amuse themselves in observing these fish leap up the
torrent. They dart themselves quite out of the water as they ascend, and
frequently fall back many times before they surmount it, and baskets made
of twigs are placed near the edge of the stream to catch them in their
fall.

I have observed, as I have sat by a spout of water, which descends
from a stone trough about two feet into a stream below, at particular
seasons of the year, a great number of little fish called minums, or
pinks, throw themselves about twenty times their own length out of the
water, expecting to get into the trough above.

This evinces that the storgee, or attention of the dam to provide for
the offspring, is strongly exerted amongst the nations of fish, where it
would seem to be the most neglected; as these salmon cannot be supposed
to attempt so difficult and dangerous a task without being conscious of
the purpose or end of their endeavours.

It is further remarkable, that most of the old salmon return to the
sea before it is proper for the young shoals to attend them, yet that a
few old ones continue in the rivers so late, that they become perfectly
emaciated by the inconvenience of their situation, and this apparently to
guide or to protect the unexperienced brood.

Of the smaller water animals we have still less knowledge, who
nevertheless probably possess many superior arts; some of these are
mentioned in Botanic Garden, P. I. Add. Note XXVII. and XXVIII. The
nympha of the water-moths of our rivers, which cover themselves with
cases of straw, gravel, and shell, contrive to make their habitations,
nearly in equilibrium with the water; when too heavy, they add a bit of
wood or straw; when too light, a bit of gravel. Edinb. Trans.

All these circumstances bear a near resemblance to the deliberate
actions of human reason.

XV. We have a very imperfect acquaintance
with the various tribes of insects: their occupations, manner of life,
and even the number of their senses, differ from our own, and from each
other; but there is reason to imagine, that those which possess the sense
of touch in the most exquisite degree, and whole occupations require the
most constant exertion of their powers, are induced with a greater
proportion or knowledge and ingenuity.

The spiders of this country manufacture nets of various forms, adapted
to various situations, to arrest the flies that are their food; and some
of them have a house or lodging-place in the middle of the net, well
contrived for warmth, security, or concealment. There is a large spider
in South America, who constructs nets of so strong a texture as to
entangle small birds, particularly the humming bird. And in Jamaica there
is another spider, who digs a hole in the earth obliquely downwards,
about three inches in length, and one inch in diameter, this cavity she
lines with a tough thick web, which when taken out resembles a leathern
purse: but what is most curious, this house has a door with hinges, like
the operculum of some sea shells; and herself and family, who tenant this
nest, open and shut the door, whenever they pass or repass. This history
was told me, and the nest with its operculum shewn me by the late Dr.
Butt of Bath, who was some years physician in Jamaica.

The production of these nets is indeed a part of the nature or
conformation of the animal, and their natural use is to supply the place
of wings, when she wishes to remove to another situation. But when she
employs them to entangle her prey, there are marks of evident design, for
she adapts the form of each net to its situation, and strengthens those
lines, that require it, by joining others to the middle of them, and
attaching those others to distant objects, with the same individual art,
that is used by mankind in supporting the masts and extending the sails
of ships. This work is executed with more mathematical exactness and
ingenuity by the field spiders, than by those in our houses, as their
constructions are more subjected to the injuries of dews and
tempests.

Besides the ingenuity shewn by these little creatures in taking their
prey, the circumstance of their counterfeiting death, when they are put
into terror, is truly wonderful; and as soon as the object of terror is
removed, they recover and run away. Some beetles are also said to possess
this piece of hypocrisy.

The curious webs, or chords, constructed by some young caterpillars to
defend themselves from cold, or from insects of prey; and by silk-worms
and some other caterpillars, when they transmigrate into aureliæ or
larvæ, have deservedly excited the admiration of the inquisitive. But our
ignorance of their manner of life, and even of the number of their
senses, totally precludes us from understanding the means by which they
acquire this knowledge.

The care of the salmon in choosing a proper situation for her spawn,
the structure of the nests of birds, their patient incubation, and the
art of the cuckoo in depositing her egg in her neighbour’s nursery, are
instances of great sagacity in those creatures: and yet they are much
inferior to the arts exerted by many of the insect tribes on similar
occasions. The hairy excrescences on briars, the oak apples, the blasted
leaves of trees, and the lumps on the backs of cows, are situations that
are rather produced than chosen by the mother insect for the convenience
of her offspring. The cells of bees, wasps, spiders, and of the various
coralline insects, equally astonish us, whether we attend to the
materials or to the architecture.

But the conduct of the ant, and of some species of the ichneumon fly
in the incubation of their eggs, is equal to any exertion of human
science. The ants many times in a day move their eggs nearer the surface
of their habitation, or deeper below it, as the heat of the weather
varies; and in colder days lie upon them in heaps for the purpose of
incubation: if their mansion is too dry, they carry them to places where
there is moisture, and you may distinctly see the little worms move and
suck up the water. When too much moisture approaches their nest, they
convey their eggs deeper in the earth, or to some other place of safety.
(Swammerd. Epil. ad Hist. Insects, p. 153. Phil. Trans. No. 23. Lowthrop.
V. 2. p. 7.)

There is one species of ichneumon-fly, that digs a hole in the earth,
and carrying into it two or three living caterpillars, deposits her eggs,
and nicely closing up the nest leaves them there; partly doubtless to
assist the incubation, and partly to supply food to her future young,
(Derham. B. 4, c. 13. Aristotle Hist. Animal, L. 5. c. 20.)

A friend of mine put about fifty large caterpillars collected from
cabbages on some bran and a few leaves into a box, and covered it with
gauze to prevent their escape. After a few days we saw, from more than
three fourths of them, about eight or ten little caterpillars of the
ichneumon-fly come out of their backs, and spin each a small cocoon of
silk, and in a few days the large caterpillars died. This small fly it
seems lays its egg in the back of the cabbage caterpillar, which when
hatched preys upon the material, which is produced there for the purpose
of making silk for the future nest of the cabbage caterpillar; of which
being deprived, the creature wanders about till it dies, and thus our
gardens are preserved by the ingenuity of this cruel fly. This curious
property of producing a silk thread, which is common to some sea animals,
see Botanic Garden, Part I. Note XXVII. and is designed for the purpose
of their transformation as in the silk-worm, is used for conveying
themselves from higher branches to lower ones of trees by some
caterpillars, and to make themselves temporary nests or tents, and by the
spider for entangling his prey. Nor is it strange that so much knowledge
should be acquired by such small animals; since there is reason to
imagine, that these insects have the sense of touch, either in their
proboscis, or their antennæ, to a great degree of perfection; and thence
may possess, as far as their sphere extends, as accurate knowledge, and
as subtle invention, as the discoverers of human arts.

XVI. 1. If we
were better acquainted with the histories of those insects that are
formed into societies, as the bees, wasps, and ants, I make no doubt but
we should find, that their arts and improvements are not so similar and
uniform as they now appear to us, but that they arose in the same manner
from experience and tradition, as the arts of our own species; though
their reasoning is from fewer ideas, is busied about fewer objects, and
is exerted with less energy.

There are some kinds of insects that migrate like the birds before
mentioned. The locust of warmer climates has sometimes come over to
England; it is shaped like a grasshopper, with very large wings, and a
body above an inch in length. It is mentioned as coming into Egypt with
an east wind, “The lord brought an east wind upon the land all that day
and night, and in the morning the east wind brought the locusts, and
covered the face of the earth, so that the land was dark,” Exod. x. 13.
The migrations of these insects are mentioned in another part of the
scripture, “The locusts have no king, yet go they forth all of them in
bands,” Prov. xxx. 27.

The accurate Mr. Adanson, near the river Gambia in Africa, was witness
to the migration of these insects. “About eight in the morning, in the
month of February, there suddenly arose over our heads a thick cloud,
which darkened the air, and deprived us of the rays of the sun. We found
it was a cloud of locusts raised about twenty or thirty fathoms from the
ground, and covering an extent of several leagues; at length a shower of
these insects descended, and after devouring every green herb, while they
rested, again resumed their flight. This cloud was brought by a strong
east-wind, and was all the morning in passing over the adjacent country.”
(Voyage to Senegal, 158.)

In this country the gnats are sometimes seen to migrate in clouds,
like the musketoes of warmer climates, and our swarms of bees frequently
travel many miles, and are said in North America always to fly towards
the south. The prophet Isaiah has a beautiful allusion to these
migrations, “The Lord shall call the fly from the rivers of Egypt, and
shall hiss for the bee that is in the land of Assyria,” Isa. vii. 18.
which has been lately explained by Mr. Bruce, in his travels to discover
the source of the Nile.

2. I am well informed that the bees that
were carried into Barbadoes, and other western islands, ceased to lay up
any honey after the first year, as they found it not useful to them: and
are now become very troublesome to the inhabitants of those islands by
infesting their sugar houses; but those in Jamaica continue to make
honey, as the cold north winds, or rainy seasons of that island, confine
them at home for several weeks together. And the bees of Senegal, which
differ from those of Europe only in size, make their honey not only
superior to ours in delicacy of flavour, but it has this singularity,
that it never concretes, but remains liquid as syrup, (Adanson). From
some observations of Mr. Wildman, and of other people of veracity, it
appears, that during the severe part of the winter season for weeks
together the bees are quite benumbed and torpid from the cold, and do not
consume any of their provision. This state of sleep, like that of
swallows and bats, seems to be the natural resource of those creatures in
cold climates, and the making of honey to be an artificial
improvement.

As the death of our hives of bees appears to be owning to their being
kept so warm, as to require food when their stock is exhausted; a very
observing gentleman at my request put two hives for many weeks into a dry
cellar, and observed, during all that time, they did not consume any of
their provision, for their weight did not decrease as it had done when
they were kept in the open air. The same observation is made in the
Annual Register for 1768, p. 113. And the Rev. Mr. White, in his Method
of preserving Bees, adds, that those on the north side of his house
consumed less honey in the winter than those on the south side.

There is another observation on bees well ascertained, that they at
various times, when the season begins to be cold, by a general motion of
their legs as they hang in clusters produce a degree of warmth, which is
easily perceptible by the hand. Hence by this ingenious exertion, they
for a long time prevent the torpid state they would naturally fall
into.

According to the late observations of Mr. Hunter, it appears that the
bee’s-wax is not made from the dust of the anthers of flowers, which they
bring home on their thighs, but that this makes what is termed bee-bread,
and is used for the purpose of feeding the bee-maggots; in the same
manner butterflies live on honey, but the previous caterpillar lives on
vegetable leaves, while the maggots of large flies require flesh for
their food, and those of the ichneumon fly require insects for their
food. What induces the bee who lives on honey to lay up vegetable powder
for its young? What induces the butterfly to lay its eggs on leaves, when
itself feeds on honey? What induces the other flies to seek a food for
their progeny different from what they consume themselves? If these are
not deductions from their own previous experience or observation, all the
actions of mankind must be resolved into instinct.

3. The dormouse consumes but little of its
food during the rigour of the season, for they roll themselves up, or
sleep, or lie torpid the greatest part of the time; but on warm sunny
days experience a short revival, and take a little food, and then relapse
into their former state.” (Pennant Zoolog. p. 67.) Other animals, that
sleep in winter without laying up any provender, are observed to go into
their winter beds fat and strong, but return to day-light in the spring
season very lean and feeble. The common flies sleep during the winter
without any provision for their nourishment, and are daily revived by the
warmth of the sun, or of our fires. These whenever they see light
endeavour to approach it, having observed, that by its greater vicinity
they get free from the degree of torpor, that the cold produces; and are
hence induced perpetually to burn themselves in our candles: deceived,
like mankind, by the misapplication of their knowledge. Whilst many of
the subterraneous insects, as the common worms, seem to retreat so deep
into the earth as not to be enlivened or awakened by the difference of
our winter days; and stop up their holes with leaves or straws, to
prevent the frosts from injuring them, or the centipes from devouring
them. The habits of peace, or the stratagems of war, of these
subterranean nations are covered from our view; but a friend of mine
prevailed on a distressed worm to enter the hole of another worm on a
bowling-green, and he presently returned much wounded about his head. And
I once saw a worm rise hastily out of the earth into the sunshine, and
observed a centipes hanging at its tail: the centipes nimbly quitted the
tail, and seizing the worm about its middle cut it in half with its
forceps, and preyed upon one part, while the other escaped. Which evinces
they have design in stopping the mouths of their habitations.

4. The wasp of this country fixes his
habitation under ground, that he may not be affected with the various
changes of our climate; but in Jamaica he hangs it on the bough of a
tree, where the seasons are less severe. He weaves a very curious paper
of vegetable fibres to cover his nest, which is constructed on the same
principle with that of the bee, but with a different material; but as his
prey consists of flesh, fruits, and insects, which are perishable
commodities, he can lay up no provender for the winter.

M. de la Loubiere, in his relation of Siam, says, “That in a part of
that kingdom, which lies open to great inundations, all the ants make
their settlements upon trees; no ants’ nests are to be seen any where
else.” Whereas in our country the ground is their only situation. From
the scriptual account of these insects, one might be led to suspect, that
in some climates they lay up a provision for the winter. Origen affirms
the same, (Cont. Cels. L. 4.) But it is generally believed that in this
country they do not, (Prov. vi. 6. xxx. 25.) The white ants of the coast
of Africa make themselves pyramids eight or ten feet high, on a base of
about the same width, with a smooth surface of rich clay, excessively
hard and well built, which appear at a distance like an assemblage of the
huts of the negroes, (Adanson). The history of these has been lately well
described in the Philosoph. Transactions, under the name of termes, or
termites. These differ very much from the nest of our large ant; but the
real history of this creature, as well as of the wasp, is yet very
imperfectly known.

Wasps are said to catch large spiders, and to cut off their legs, and
carry their mutilated bodies to their young, Dict. Raison. Tom. I. p.
152.

One circumstance I shall relate which fell under my own eye, and
shewed the power or reason in a wasp, as it is exercised among men. A
wasp, on a gravel walk, had caught a fly nearly as large as himself;
kneeling on the ground I observed him separate the tail and the head from
the body part, to which the wings were attached. He then took the body
part in his paws, and rose about two feet from the ground with it; but a
gentle breeze wafting the wings of the fly turned him round in the air,
and he settled again with his prey upon the gravel. I then distinctly
observed him cut off with his mouth, first one of the wings, and then the
other, after which he flew away with it unmolested by the wind.

Go, thou sluggard, learn arts and industry from the bee, and from the
ant!

Go, proud reasoner, and call the worm thy sister!

XVII. Conclusion.

It was before observed how much the superior accuracy of our sense of
touch contributes to increase our knowledge; but it is the greater energy
and activity of the power of volition (as explained in the former
Sections of this work) that marks mankind, and has given him the empire
of the world.

There is a criterion by which we may distinguish our voluntary acts or
thoughts from those that are excited by our sensations: “The former are
always employed about the means to acquire pleasureable objects,
or to avoid painful ones: while the latter are employed about the
possession of those that are already in our power.”

If we turn our eyes upon the fabric of our fellow animals, we find
they are supported with bones, covered with skins, moved by muscles; that
they possess the same senses, acknowledge the same appetites, and are
nourished by the same aliment with ourselves; and we should hence
conclude from the strongest analogy, that their internal faculties were
also in some measure similar to our own.

Mr. Locke indeed published an opinion, that other animals possessed no
abstract or general ideas, and thought this circumstance was the barrier
between the brute and the human world. But these abstracted ideas have
been since demonstrated by Bishop Berkley, and allowed by Mr. Hume, to
have no existence in nature, not even in the mind of their inventor, and
we are hence necessitated to look for some other mark of distinction.

The ideas and actions of brutes, like those of children, are almost
perpetually produced by their present pleasures, or their present pains;
and, except in the few instances that have been mentioned in this
Section, they seldom busy themselves about the means of procuring
future bliss, or of avoiding future misery.

Whilst the acquiring of languages, the making of tools, and the
labouring for money; which are all only the means of procuring
pleasure; and the praying to the Deity, as another means to
procure happiness, are characteristic of human nature.

SECT. XVII.

THE CATENATION OF MOTIONS.

I. 1.
Catenations of animal motion. 2.
Are produced by irritations, by sensations, by volitions. 3. They continue some time after they have
been excited. Cause of catenation. 4.
We can then exert our attention on other objects. 5. Many catenations of motions go on
together. 6. Some links of the
catenations of motions may be left out without disuniting the chain.
7. Interrupted circles of motion continue
confusedly till they come to the part of the circle, where they were
disturbed. 8. Weaker catenations are
dissevered by stronger. 9. Then new
catenations take place. 10. Much
effort prevents their reuniting. Impediment of speech. 11. Trains more easily dissevered than
circles. 12. Sleep destroys volition
and external stimulus. II. Instances of
various catenations in a young lady playing on the harpsichord. III. 1. What
catenations are the strongest. 2.
Irritations joined with associations from strongest connexions. Vital
motions. 3. New links with increased
force, cold fits of fever produced. 4.
New links with decreased force. Cold bath. 5. Irritation joined with sensation.
Inflammatory fever. Why children cannot tickle themselves. 6. Volition joined with sensation. Irritative
ideas of sound become sensible. 7.
Ideas of imagination, dissevered by irritations, by volition,
production of surprise.

I. 1. To
investigate with precision the catenations of animal motions, it would be
well to attend to the manner of their production; but we cannot begin
this disquisition early enough for this purpose, as the catenations of
motion seem to begin with life, and are only extinguishable with it; We
have spoken of the power of irritation, of sensation, of volition, and of
association, as preceding the fibrous motions; we now step forwards, and
consider, that conversely they are in their turn preceded by those
motions; and that all the successive trains or circles of our actions are
composed of this twofold concatenation. Those we shall call trains of
action, which continue to proceed without any stated repetitions; and
those circles of action, when the parts of them return at certain
periods, though the trains, of which they consist, are not exactly
similar. The reading an epic poem is a train of actions; the reading a
song with a chorus at equal distances in the measure constitutes so many
circles of action.

2. Some catenations of animal motion are
produced by reiterated successive irritations, as when we learn to repeat
the alphabet in its order by frequently reading the letters of it. Thus
the vermicular motions of the bowels were originally produced by the
successive irritations of the passing aliment; and the succession of
actions of the auricles and ventricles of the heart was originally formed
by successive stimulus of the blood, these afterwards become part of the
diurnal circles of animal actions, as appears by the periodical returns
of hunger, and the quickened pulse of weak people in the evening.

Other catenations of animal motion are gradually acquired by
successive agreeable sensations, as in learning a favourite song or
dance; others by disagreeable sensations, as in coughing or nictitation;
these become associated by frequent repetition, and afterwards compose
parts of greater circles of action like those above mentioned.

Other catenations of motions are gradually acquired by frequent
voluntary repetitions; as when we deliberately learn to march, read,
fence, or any mechanic art, the motions of many of our muscles become
gradually linked together in trains, tribes, or circles of action. Thus
when any one at first begins to use the tools in turning wood or metals
in a lathe, he wills the motions of his hand or fingers, till at length
these actions become so connected with the effect, that he seems only to
will the point of the chisel. These are caused by volition, connected by
association like those above described, and afterwards become parts of
our diurnal trains or circles of action.

3. All these catenations of animal
motions, are liable to proceed some time after they are excited, unless
they are disturbed or impeded by other irritations, sensations, or
volitions; and in many instances in spite of our endeavours to stop them;
and this property of animal motions is probably the cause of their
catenation. Thus when a child revolves some minute on one foot, the
spectra of the ambient objects appear to circulate round him some time
after he falls upon the ground. Thus the palpitation of the heart
continues some time after the object of fear, which occasioned it, is
removed. The blush of shame, which is an excess of sensation, and the
glow of anger, which is an excess of volition, continue some time, though
the affected person finds, that those emotions were caused by mistaken
facts, and endeavours to extinguish their appearance. See Sect. XII. 1. 5.

4. When a circle of motions becomes
connected, by frequent repetitions as above, we can exert our attention
strongly on other objects, and the concatenated circle of motions will
nevertheless proceed in due order; as whilst you are thinking on this
subject, you use variety of muscles in walking about your parlour, or in
sitting at your writing-table.

5. Innumerable catenations of motions may
proceed at the same time, without incommoding each other. Of these are
the motions of the heart and arteries; those of digestion and glandular
secretion; of the ideas, or sensual motions; those of progression, and of
speaking; the great annual circle of actions so apparent in birds in
their times of breeding and moulting; the monthly circles of many female
animals; and the diurnal circles of sleeping and waking, of fulness and
inanition.

6. Some links of successive trains or of
synchronous tribes of action may be left out without disjoining the
whole. Such are our usual trains of recollection; after having travelled
through an entertaining country, and viewed many delightful lawns,
rolling rivers, and echoing rocks; in the recollection of our journey we
leave out the many districts, that we crossed, which were marked with no
peculiar pleasure. Such also are our complex ideas, they are catenated
tribes of ideas, which do not perfectly resemble their correspondent
perceptions, because some of the parts are omitted.

7. If an interrupted circle of actions is
not entirely dissevered, it will continue to proceed confusedly, till it
comes to the part of the circle, where it was interrupted.

The vital motions in a fever from drunkenness, and in other periodical
diseases, are instances of this circumstance. The accidental inebriate
does not recover himself perfectly till about the same hour on the
succeeding day. The accustomed drunkard is disordered, if he has not his
usual potation of fermented liquor. So if a considerable part of a
connected tribe of action be disturbed, that whole tribe goes on with
confusion, till the part of the tribe affected regains its accustomed
catenations. So vertigo produces vomiting, and a great secretion of bile,
as in sea-sickness, all these being parts of the tribe of irritative
catenations.

8. Weaker catenated trains may be
dissevered by the sudden exertion of the stronger. When a child first
attempts to walk across a room, call to him, and he instantly falls upon
the ground. So while I am thinking over the virtues of my friends, if the
tea-kettle spurt out some hot water on my stocking; the sudden pain
breaks the weaker chain of ideas, and introduces a new group of figures
of its own. This circumstance is extended to some unnatural trains of
action, which have not been confirmed by long habit; as the hiccough, or
an ague-fit, which are frequently curable by surprise. A young lady about
eleven years old had for five days had a contraction of one muscle in her
fore arm, and another in her arm, which occurred four or five times every
minute; the muscles were seen to leap, but without bending the arm. To
counteract this new morbid habit, an issue was placed over the convulsed
muscle of her arm, and an adhesive plaster wrapped tight like a bandage
over the whole fore arm, by which the new motions were immediately
destroyed, but the means were continued some weeks to prevent a
return.

9. If any circle of actions is dissevered,
either by omission of some of the links, as in sleep, or by insertion of
other links, as in surprise, new catenations take place in a greater or
less degree. The last link of the broken chain of actions becomes
connected with the new motion which has broken it, or with that which was
nearest the link omitted; and these new catenations proceed instead of
the old ones. Hence the periodic returns of ague-fits, and the chimeras
of our dreams.

10. If a train of actions is dissevered,
much effort of volition or sensation will prevent its being restored.
Thus in the common impediment of speech, when the association of the
motions of the muscles of enunciation with the idea of the word to be
spoken is disordered, the great voluntary efforts, which distort the
countenance, prevent the rejoining of the broken associations. See No. II. 10. of this Section. It is thus likewise
observable in some inflammations of the bowels, the too strong efforts
made by the muscles to carry forwards the offending material fixes it
more firmly in its place, and prevents the cure. So in endeavouring to
recal to our memory some particular word of a sentence, if we exert
ourselves too strongly about it, we are less likely to regain it.

11. Catenated trains or tribes of action
are easier dissevered than catenated circles of action. Hence in
epileptic fits the synchronous connected tribes of action, which keep the
body erect, are dissevered, but the circle of vital motions continues
undisturbed.

12. Sleep destroys the power of volition,
and precludes the stimuli of external objects, and thence dissevers the
trains, of which these are a part; which confirms the other catenations,
as those of the vital motions, secretions, and absorptions; and produces
the new trains of ideas, which constitute our dreams.

II. 1. All the
preceding circumstances of the catenations of animal motions will be more
clearly understood by the following example of a person learning music;
and when we recollect the variety of mechanic arts, which are performed
by associated trains of muscular actions catenated with the effects they
produce, as in knitting, netting, weaving; and the greater variety of
associated trains of ideas caused or catenated by volitions or
sensations, as in our hourly modes of reasoning, or imagining, or
recollecting, we shall gain some idea of the innumerable catenated trains
and circles of action, which form the tenor of our lives, and which
began, and will only cease entirely with them.

2. When a young lady begins to learn
music, she voluntarily applies herself to the characters of her
music-book, and by many repetitions endeavours to catenate them with the
proportions of sound, of which they are symbols. The ideas excited by the
musical characters are slowly connected with the keys of the harpsichord,
and much effort is necessary to produce every note with the proper
finger, and in its due place and time; till at length a train of
voluntary exertions becomes catenated with certain irritations. As the
various notes by frequent repetitions become connected in the order, in
which they are produced, a new catenation of sensitive exertions becomes
mixed with the voluntary ones above described; and not only the musical
symbols of crotchets and quavers, but the auditory notes and tones at the
same time, become so many successive or synchronous links in this circle
of catenated actions.

At length the motions of her fingers become catenated with the musical
characters; and these no sooner strike the eye, than the finger presses
down the key without any voluntary attention between them; the activity
of the hand being connected with the irritation of the figure or place of
the musical symbol on the retina; till at length by frequent repetitions
of the same tune the movements of her fingers in playing, and the muscles
of the larynx in singing, become associated with each other, and form
part of those intricate trains and circles of catenated motions,
according with the second article of the preceding propositions in No. 1. of this Section.

3. Besides the facility, which by habit
attends the execution of this musical performance, a curious circumstance
occurs, which is, that when our young musician has began a tune, she
finds herself inclined to continue it; and that even when she is
carelessly singing alone without attending to her own song; according
with the third preceding article.

4. At the same time that our young
performer continues to play with great exactness this accustomed tune,
she can bend her mind, and that intensely, on some other object,
according with the fourth article of the preceding proportions.

The manuscript copy of this work was lent to many of my friends at
different times for the purpose of gaining their opinions and criticisms
on many parts of it, and I found the following anecdote written with a
pencil opposite to this page, but am not certain by whom. “I remember
seeing the pretty young actress, who succeeded Mrs. Arne in the
performance of the celebrated Padlock, rehearse the musical parts at her
harpsichord under the eye of her master with great taste and accuracy;
though I observed her countenance full of emotion, which I could not
account for; at last she suddenly burst into tears; for she had all this
time been eyeing a beloved canary bird, suffering great agonies, which at
that instant fell dead from its perch.”

5. At the same time many other catenated
circles of action are going on in the person of our fair musician, as
well as the motions of her fingers, such as the vital motions,
respiration, the movements of her eyes and eyelids, and of the intricate
muscles of vocality, according with the fifth preceding article.

6. If by any strong impression on the mind
of our fair musician she should be interrupted for a very inconsiderable
time, she can still continue her performance, according to the sixth
article.

7. If however this interruption be
greater, though the chain of actions be not dissevered, it proceeds
confusedly, and our young performer continues indeed to play, but in a
hurry without accuracy and elegance, till she begins the tune again,
according to the seventh of the preceding articles.

8. But if this interruption be still
greater, the circle of actions becomes entirely dissevered, and she finds
herself immediately under the necessity to begin over again to recover
the lost catenation, according to the eighth preceding article.

9. Or in trying to recover it she will
sing some dissonant notes, or strike some improper keys, according to the
ninth preceding article.

10. A very remarkable thing attends this
breach of catenation, if the performer has forgotten some word of her
song, the more energy of mind she uses about it, the more distant is she
from regaining it; and artfully employs her mind in part on some other
object, or endeavours to dull its perceptions, continuing to repeat, as
it were inconsciously, the former part of the song, that she remembers,
in hopes to regain the lost connexion.

For if the activity of the mind itself be more energetic, or takes its
attention more, than the connecting word, which is wanted; it will not
perceive the slighter link of this lost word; as who listens to a feeble
sound, must be very silent and motionless; so that in this case the very
vigour of the mind itself seems to prevent it from regaining the lost
catenation, as well as the too great exertion in endeavouring to regain
it, according to the tenth preceding article.

We frequently experience, when we are doubtful about the spelling of a
word, that the greater voluntary exertion we use, that is the more
intensely we think about it, the further are we from regaining the lost
association between the letters of it, but which readily recurs when we
have become careless about it. In the same manner, after having for an
hour laboured to recollect the name of some absent person, it shall seem,
particularly after sleep, to come into the mind as it were spontaneously;
that is the word we are in search of, was joined to the preceding one by
association; this association being dissevered, we endeavour to recover
it by volition; this very action of the mind strikes our attention more,
than the faint link of association, and we find it impossible by this
means to retrieve the lost word. After sleep, when volition is entirely
suspended, the mind becomes capable of perceiving the fainter link of
association, and the word is regained.

On this circumstance depends the impediment of speech before
mentioned; the first syllable of a word is causable by volition, but the
remainder of it is in common conversation introduced by its associations
with this first syllable acquired by long habit. Hence when the mind of
the stammerer is vehemently employed on some idea of ambition of shining,
or fear of not succeeding, the associations of the motions of the muscles
of articulation with each other become dissevered by this greater
exertion, and he endeavours in vain by voluntary efforts to rejoin the
broken association. For this purpose he continues to repeat the first
syllable, which is causable by volition, and strives in vain, by various
distortions of countenance, to produce the next links, which are subject
to association. See Class IV. 3. 1. 1.

11. After our accomplished musician has
acquired great variety of tunes and songs, so that some of them begin to
cease to be easily recollected, she finds progressive trains of musical
notes more frequently forgotten, than those which are composed of
reiterated circles, according with the eleventh preceding article.

12. To finish our example with the
preceding articles we must at length suppose, that our fair performer
falls asleep over her harpsichord; and thus by the suspension of
volition, and the exclusion of external stimuli, she dissevers the trains
and circles of her musical exertions.

III. 1. Many of
these circumstances of catenations of motions receive an easy explanation
from the four following consequences to the seventh law of animal
causation in Sect. IV. These are, first, that
those successions or combinations of animal motions, whether they were
united by causation, association, or catenation, which have been most
frequently repeated, acquire the strongest connection. Secondly, that of
these, those, which have been less frequently mixed with other trains or
tribes of motion, have the strongest connection. Thirdly, that of these,
those, which were first formed, have the strongest connection. Fourthly,
that if an animal motion be excited by more than one causation,
association, or catenation, at the same time, it will be performed with
greater energy.

2. Hence also we understand, why the
catenations of irritative motions are more strongly connected than those
of the other classes, where the quantity of unmixed repetition has been
equal; because they were first formed. Such are those of the secerning
and absorbent systems of vessels, where the action of the gland produces
a fluid, which stimulates the mouths of its correspondent absorbents. The
associated motions seem to be the next most strongly united, from their
frequent repetition; and where both these circumstances unite, as in the
vital motions, their catenations are indissoluble but by the destruction
of the animal.

3. Where a new link has been introduced
into a circle of actions by some accidental defect of stimulus; if that
defect of stimulus be repeated at the same part of the circle a second or
a third time, the defective motions thus produced, both by the repeated
defect of stimulus and by their catenation with the parts of the circle
of actions, will be performed with less and less energy. Thus if any
person is exposed to cold at a certain hour to-day, so long as to render
some part of the system for a time torpid; and is again exposed to it at
the same hour to-morrow, and the next day; he will be more and more
affected by it, till at length a cold fit of fever is completely formed,
as happens at the beginning of many of those fevers, which are called
nervous or low fevers. Where the patient has slight periodical shiverings
and paleness for many days before the febrile paroxysm is completely
formed.

4. On the contrary, if the exposure to
cold be for so short a time, as not to induce any considerable degree of
torpor or quiescence, and is repeated daily as above mentioned, it loses
its effect more and more at every repetition, till the constitution can
bear it without inconvenience, or indeed without being conscious of it.
As in walking into the cold air in frosty weather. The same rule is
applicable to increased stimulus, as of heat, or of vinous spirit, within
certain limits, as is applied in the two last paragraphs to Deficient
Stimulus; as is further explained in Sect. XXXVI. on the Periods of Diseases.

5. Where irritation coincides with
sensation to produce the same catenations of motion, as in inflammatory
fevers, they are excited with still greater energy than by the irritation
alone. So when children expect to be tickled in play, by a feather
lightly passed over the lips, or by gently vellicating the soles of their
feet, laughter is most vehemently excited; though they can stimulate
these parts with their own fingers unmoved. Here the pleasureable idea of
playfulness coincides with the vellication; and there is no voluntary
exertion used to diminish the sensation, as there would be, if a child
should endeavour to tickle himself. See Sect. XXXIV. 1. 4.

6. And lastly, the motions excited by the
junction of voluntary exertion with irritation are performed with more
energy, than those by irritation singly; as when we listen to small
noises, as to the ticking of a watch in the night, we perceive the most
weak sounds, that are at other times unheeded. So when we attend to the
irritative ideas of sound in our ears, which are generally not attended
to, we can hear them; and can see the spectra of objects, which remain in
the eye, whenever we please to exert our voluntary power in aid of those
weak actions of the retina, or of the auditory nerve.

7. The temporary catenations of ideas,
which are caused by the sensations of pleasure or pain, are easily
dissevered either by irritations, as when a sudden noise disturbs a
day-dream; or by the power of volition, as when we awake from sleep.
Hence in our waking hours, whenever an idea occurs, which is incongruous
to our former experience, we instantly dissever the train of imagination
by the power of volition, and compare the incongruous idea with our
previous knowledge of nature, and reject it. This operation of the mind
has not yet acquired a specific name, though it is exerted every minute
of our waking hours; unless it may be termed INTUITIVE
ANALOGY. It is an act of reasoning of which we are unconscious
except from its effects in preserving the congruity of our ideas, and
bears the same relation to the sensorial power of volition, that
irritative ideas, of which we are inconscious except by their effects, do
to the sensorial power of irritation; as the former is produced by
volition without our attention to it, and the latter by irritation
without our attention to them.

If on the other hand a train of imagination or of voluntary ideas are
excited with great energy, and passing on with great vivacity, and become
dissevered by some violent stimulus, as the discharge of a pistol near
one’s ear, another circumstance takes place, which is termed SURPRISE; which by exciting violent irritation, and
violent sensation, employs for a time the whole sensorial energy, and
thus dissevers the passing trains of ideas, before the power of volition
has time to compare them with the usual phenomena of nature. In this case
fear is generally the companion of surprise, and adds to our
embarrassment, as every one experiences in some degree when he hears a
noise in the dark, which he cannot instantly account for. This catenation
of fear with surprise is owing to our perpetual experience of injuries
from external bodies in motion, unless we are upon our guard against
them. See Sect. XVIII. 17. XIX. 2.

Many other examples of the catenations of animal motions are explained
in Sect. XXXVI. on the Periods of Diseases.

SECT. XVIII.

OF SLEEP.

1. Volition is suspended in sleep.
2. Sensation continues. Dreams prevent
delirium and inflammation. 3.
Nightmare. 4. Ceaseless flow of
ideas in dreams. 5. We seem to receive
them by the senses. Optic nerve perfectly sensible in sleep. Eyes less
dazzled after dreaming of visible objects. 6. Reverie, belief. 7. How we distinguish ideas from
perceptions. 8. Variety of scenery in
dreams, excellence of the sense of vision. 9. Novelty of combination in dreams. 10. Distinctness of imagery in dreams.
11. Rapidity of transaction in
dreams. 12. Of measuring time. Of
dramatic time and place. Why a dull play induces sleep, and an
interesting one reverie. 13.
Consciousness of our existence and identity in dreams. 14. How we awake sometimes suddenly,
sometimes frequently. 15. Irritative
motions continue in sleep, internal irritations are succeeded by
sensation. Sensibility increases during sleep, and irritability. Morning
dreams. Why epilepsies occur in sleep. Ecstacy of children. Case of
convulsions in sleep. Cramp, why painful. Asthma. Morning sweats.
Increase of heat. Increase of urine in sleep. Why more liable to take
cold in sleep. Catarrh from thin night-caps. Why we feel chilly at the
approach of sleep, and at waking in the open air. 16. Why the gout commences in sleep.
Secretions are more copious in sleep, young animals and plants grow more
in sleep. 17. Inconsistency of
dreams. Absence of surprise in dreams. 18. Why we forget some dreams and not
others. 19. Sleep-talkers awake with
surprise. 20. Remote causes of sleep.
Atmosphere with less oxygene. Compression of the brain in spina bifida.
By whirling on an horizontal wheel. By cold. 21. Definition of sleep.

1. There are four situations of our system,
which in their moderate degrees are not usually termed diseases, and yet
abound with many very curious and instructive phenomena; these are sleep,
reverie, vertigo, drunkenness. These we shall previously consider, before
we step forwards to develop the causes and cures of diseases with the
modes of the operation of medicines.

As all those trains and tribes of animal motion, which are subjected
to volition, were the last that were caused, their connection is weaker
than that of the other classes; and there is a peculiar circumstance
attending this causation, which is, that it is entirely suspended during
sleep; whilst the other classes of motion, which are more immediately
necessary to life, as those caused by internal stimuli, for instance the
pulsations of the heart and arteries, or those catenated with pleasurable
sensation, as the powers of digestion, continue to strengthen their
habits without interruption. Thus though man in his sleeping state is a
much less perfect animal, than in his waking hours; and though he
consumes more than one third of his life in this his irrational
situation; yet is the wisdom of the Author of nature manifest even in
this seeming imperfection of his work!

The truth of this assertion with respect to the large muscles of the
body, which are concerned in locomotion, is evident; as no one in perfect
sanity walks about in his sleep, or performs any domestic offices: and in
respect to the mind, we never exercise our reason or recollection in
dreams; we may sometimes seem distracted between contending passions, but
we never compare their objects, or deliberate about the acquisition of
those objects, if our sleep is perfect. And though many synchronous
tribes or successive trains of ideas may represent the houses or walks,
which have real existence, yet are they here introduced by their
connection with our sensations, and are in truth ideas of imagination,
not of recollection.

2. For our sensations of pleasure and pain
are experienced with great vivacity in our dreams; and hence all that
motley group of ideas, which are caused by them, called the ideas of
imagination, with their various associated trains, are in a very vivid
manner acted over in the sensorium; and these sometimes call into action
the larger muscles, which have been much associated with them; as appears
from the muttering sentences, which some people utter in their dreams,
and from the obscure barking of sleeping dogs, and the motions of their
feet and nostrils.

This perpetual flow of the trains of ideas, which constitute our
dreams, and which are caused by painful or pleasurable sensation, might
at first view be conceived to be an useless expenditure of sensorial
power. But it has been shewn, that those motions, which are perpetually
excited, as those of the arterial system by the stimulus of the blood,
are attended by a great accumulation of sensorial power, after they have
been for a time suspended; as the hot-fit of fever is the consequence of
the cold one. Now as these trains of ideas caused by sensation are
perpetually excited during our waking hours, if they were to be suspended
in sleep like the voluntary motions, (which are exerted only by intervals
during our waking hours,) an accumulation of sensorial power would
follow; and on our awaking a delirium would supervene, since these ideas
caused by sensation would be produced with such energy, that we should
mistake the trains of imagination for ideas excited by irritation; as
perpetually happens to people debilitated by fevers on their first
awaking; for in these fevers with debility the general quantity of
irritation being diminished, that of sensation is increased. In like
manner if the actions of the stomach, intestines, and various glands,
which are perhaps in part at least caused by or catenated with agreeable
sensation, and which perpetually exist during our waking hours, were like
the voluntary motions suspended in our sleep; the great accumulation of
sensorial power, which would necessarily follow, would be liable to
excite inflammation in them.

3. When by our continued posture in sleep,
some uneasy sensations are produced, we either gradually awake by the
exertion of volition, or the muscles connected by habit with such
sensations alter the position of the body; but where the sleep is
uncommonly profound, and those uneasy sensations great, the disease
called the incubus, or nightmare, is produced. Here the desire of moving
the body is painfully exerted, by the power of moving it, or volition, is
incapable of action, till we awake. Many less disagreeable struggles in
our dreams, as when we wish in vain to fly from terrifying objects,
constitute a slighter degree of this disease. In awaking from the
nightmare I have more than once observed, that there was no disorder in
my pulse; nor do I believe the respiration is laborious, as some have
affirmed. It occurs to people whose sleep is too profound, and some
disagreeable sensation exists, which at other times would have awakened
them, and have thence prevented the disease of nightmare; as after great
fatigue or hunger with too large a supper and wine, which occasion our
sleep to be uncommonly profound. See No. 14,
of this Section.

4. As the larger muscles of the body are
much more frequently excited by volition than by sensation, they are but
seldom brought into action in our sleep: but the ideas of the mind are by
habit much more frequently connected with sensation than with volition;
and hence the ceaseless flow of our ideas in dreams. Every one’s
experience will teach him this truth, for we all daily exert much
voluntary muscular motion: but few of mankind can bear the fatigue of
much voluntary thinking.

5. A very curious circumstance attending
these our sleeping imaginations is, that we seem to receive them by the
senses. The muscles, which are subservient to the external organs of
sense, are connected with volition, and cease to act in sleep; hence the
eyelids are closed, and the tympanum of the ear relaxed; and it is
probable a similarity of voluntary exertion may be necessary for the
perceptions of the other nerves of sense; for it is observed that the
papillæ of the tongue can be seen to become erected, when we attempt to
taste any thing extremely grateful. Hewson Exper. Enquir. V. 2. 186.
Albini Annot. Acad. L. i. c. 15. Add to this, that the immediate organs
of sense have no objects to excite them in the darkness and silence of
the night, but their nerves of sense nevertheless continue to possess
their perfect activity subservient to all their numerous sensitive
connections. This vivacity of our nerves of sense during the time of
sleep is evinced by a circumstance, which almost every one must at some
time or other have experienced; that is, if we sleep in the daylight, and
endeavour to see some object in our dream, the light is exceedingly
painful to our eyes; and after repeated struggles we lament in our sleep,
that we cannot see it. In this case I apprehend the eyelid is in some
degree opened by the vehemence of our sensations; and, the iris being
dilated, the optic nerve shews as great or greater sensibility than in
our waking hours. See No. 15. of this
Section.

When we are forcibly waked at midnight from profound sleep, our eyes
are much dazzled with the light of the candle for a minute or two, after
there has been sufficient time allowed for the contraction of the iris;
which is owing to the accumulation of sensorial power in the organ of
vision during its state of less activity. But when we have dreamt much of
visible objects, this accumulation of sensorial power in the organ of
vision is lessened or prevented, and we awake in the morning without
being dazzled with the light, after the iris has had time to contract
itself. This is a matter of great curiosity, and may be thus tried by any
one in the day-light. Close your eyes, and cover them with your hat;
think for a minute on a tune, which you are accustomed to, and endeavour
to sing it with as little activity of mind as possible. Suddenly uncover
and open your eyes, and in one second of time the iris will contract
itself, but you will perceive the day more luminous for several seconds,
owing to the accumulation of sensorial power in the optic nerve.

Then again close and cover your eyes, and think intensely on a cube of
ivory two inches diameter, attending first to the north and south sides
of it, and then to the other four sides of it; then get a clear image in
your mind’s eye of all the sides of the same cube coloured red; and then
of it coloured green; and then of it coloured blue; lastly, open your
eyes as in the former experiment, and after the first second of time
allowed for the contraction of the iris, you will not perceive any
increase of the light of the day, or dazzling; because now there is no
accumulation of sensorial power in the optic nerve; that having been
expended by its action in thinking over visible objects.

This experiment is not easy to be made at first, but by a few patient
trials the fact appears very certain; and shews clearly, that our ideas
of imagination are repetitions of the motions of the nerve, which were
originally occasioned by the stimulus of external bodies; because they
equally expend the sensorial power in the organ of sense. See Sect. III. 4. which is analogous to our being as much
fatigued by thinking as by labour.

6. Nor is it in our dreams alone, but even
in our waking reveries, and in great efforts of invention, so great is
the vivacity of our ideas, that we do not for a time distinguish them
from the real presence of substantial objects; though the external organs
of sense are open, and surrounded with their usual stimuli. Thus whilst I
am thinking over the beautiful valley, through which I yesterday
travelled, I do not perceive the furniture of my room: and there are
some, whose waking imaginations are so apt to run into perfect reverie,
that in their common attention to a favourite idea they do not hear the
voice of the companion, who accosts them, unless it is repeated with
unusual energy.

This perpetual mistake in dreams and reveries, where our ideas of
imagination are attended with a belief of the presence of external
objects, evinces beyond a doubt, that all our ideas are repetitions of
the motions of the nerves of sense, by which they were acquired; and that
this belief is not, as some late philosophers contend, an instinct
necessarily connected only with our perceptions.

7. A curious question demands our attention
in this place; as we do not distinguish in our dreams and reveries
between our perceptions of external objects, and our ideas of them in
their absence, how do we distinguish them at any time? In a dream, if the
sweetness of sugar occurs to my imagination, the whiteness and hardness
of it, which were ideas usually connected with the sweetness, immediately
follow in the train; and I believe a material lump of sugar present
before my senses: but in my waking hours, if the sweetness occurs to my
imagination, the stimulus of the table to my hand, or of the window to my
eye, prevents the other ideas of the hardness and whiteness of the sugar
from succeeding; and hence I perceive the fallacy, and disbelieve the
existence of objects correspondent to those ideas, whose tribes or trains
are broken by the stimulus of other objects. And further in our waking
hours, we frequently exert our volition in comparing present appearances
with such, as we have usually observed; and thus correct the errors of
one sense by our general knowledge of nature by intuitive analogy. See
Sect. XVII. 3. 7. Whereas in dreams the
power of volition is suspended, we can recollect and compare our present
ideas with none of our acquired knowledge, and are hence incapable of
observing any absurdities in them.

By this criterion we distinguish our waking from our sleeping hours,
we can voluntarily recollect our sleeping ideas, when we are awake, and
compare them with our waking ones; but we cannot in our sleep
voluntarily recollect our waking ideas at all.

8. The vast variety of scenery, novelty of
combination, and distinctness of imagery, are other curious circumstances
of our sleeping imaginations. The variety of scenery seems to arise from
the superior activity and excellence of our sense of vision; which in an
instant unfolds to the mind extensive fields of pleasurable ideas; while
the other senses collect their objects slowly, and with little
combination; add to this, that the ideas, which this organ presents us
with, are more frequently connected with our sensation than those of any
other.

9. The great novelty of combination is
owing to another circumstance; the trains of ideas, which are carried on
in our waking thoughts, are in our dreams dissevered in a thousand places
by the suspension of volition, and the absence of irritative ideas, and
are hence perpetually falling into new catenations. As explained in Sect.
XVII. 1. 9. For the power of volition is
perpetually exerted during our waking hours in comparing our passing
trains of ideas with our acquired knowledge of nature, and thus forms
many intermediate links in their catenation. And the irritative ideas
excited by the stimulus of the objects, with which we are surrounded, are
every moment intruded upon us, and form other links of our unceasing
catenations of ideas.

10. The absence of the stimuli of external
bodies, and of volition, in our dreams renders the organs of sense liable
to be more strongly affected by the powers of sensation, and of
association. For our desires or aversions, or the obtrusions of
surrounding bodies, dissever the sensitive and associate tribes of ideas
in our waking hours by introducing those of irritation and volition
amongst them. Hence proceeds the superior distinctness of pleasurable or
painful imagery in our sleep; for we recal the figure and the features of
a long lost friend, whom we loved, in our dreams with much more accuracy
and vivacity than in our waking thoughts. This circumstance contributes
to prove, that our ideas of imagination are reiterations of those motions
of our organs of sense, which were excited by external objects; because
while we are exposed to the stimuli of present objects, our ideas of
absent objects cannot be so distinctly formed.

11. The rapidity of the succession of
transactions in our dreams is almost inconceivable; insomuch that, when
we are accidentally awakened by the jarring of a door, which is opened
into our bed-chamber, we sometimes dream a whole history of thieves or
fire in the very instant of awaking.

During the suspension of volition we cannot compare our other ideas
with those of the parts of time in which they exist; that is, we cannot
compare the imaginary scene, which is before us, with those changes of
it, which precede or follow it: because this act of comparing requires
recollection or voluntary exertion. Whereas in our waking hours, we are
perpetually making this comparison, and by that means our waking ideas
are kept confident with each other by intuitive analogy; but this
companion retards the succession of them, by occasioning their
repetition. Add to this, that the transactions of our dreams consist
chiefly of visible ideas, and that a whole history of thieves and fire
may be beheld in an instant of time like the figures in a
picture.

12. From this incapacity of attending to
the parts of time in our dreams, arises our ignorance of the length of
the night; which, but from our constant experience to the contrary, we
should conclude was but a few minutes, when our sleep is perfect. The
same happens in our reveries; thus when we are possessed with vehement
joy, grief, or anger, time appears short, for we exert no volition to
compare the present scenery with the past or future; but when we are
compelled to perform those exercises of mind or body, which, are unmixed
with passion, as in travelling over a dreary country, time appears long;
for our desire to finish our journey occasions us more frequently to
compare our present situation with the parts of time or place, which are
before and behind us.

So when we are enveloped in deep contemplation of any kind, or in
reverie, as in reading a very interesting play or romance, we measure
time very inaccurately; and hence, if a play greatly affects our
passions, the absurdities of passing over many days or years, and or
perpetual changes of place, are not perceived by the audience; as is
experienced by every one, who reads or sees some plays of the immortal
Shakespear; but it is necessary for inferior authors to observe those
rules of the πιθανον and πρεπον inculcated by
Aristotle, because their works do not interest the passions sufficiently
to produce complete reverie.

Those works, however, whether a romance or a sermon, which do not
interest us so much as to induce reverie, may nevertheless incline us to
sleep. For those pleasurable ideas, which are presented to us, and are
too gentle to excite laughter, (which is attended with interrupted
voluntary exertions, as explained Sect. XXXIV.
1. 4.) and which are not accompanied with any other emotion, which
usually excites some voluntary exertion, as anger, or fear, are liable to
produce sleep; which consists in a suspension of all voluntary power. But
if the ideas thus presented to us, and interest our attention, are
accompanied with so much pleasurable or painful sensation as to excite
our voluntary exertion at the same time, reverie is the consequence.
Hence an interesting play produces reverie, a tedious one produces sleep:
in the latter we become exhausted by attention, and are not excited to
any voluntary exertion, and therefore sleep; in the former we are excited
by some emotion, which prevents by its pain the suspension of volition,
and in as much as it interests us, induces reverie, as explained in the
next Section.

But when our sleep is imperfect, as when we have determined to rise in
half an hour, time appears longer to us than in most other situations.
Here our solicitude not to oversleep the determined time induces us in
this imperfect sleep to compare the quick changes of imagined scenery
with the parts of time or place, they would have taken up, had they real
exigence; and that more frequently than in our waking hours; and hence
the time appears longer to us: and I make no doubt, but the permitted
time appears long to a man going to the gallows, as the fear of its quick
lapse will make him think frequently about it.

13. As we gain our knowledge of time by
comparing the present scenery with the past and future, and of place by
comparing the situations of objects with each other; so we gain our idea
of consciousness by comparing ourselves with the scenery around us; and
of identity by comparing our present consciousness with our past
consciousness: as we never think of time or place, but when we make the
companions above mentioned, so we never think of consciousness, but when
we compare our own existence with that of other objects; nor of identity,
but when we compare our present and our past consciousness. Hence the
consciousness of our own existence, and of our identity, is owing to a
voluntary exertion of our minds: and on that account in our complete
dreams we neither measure time, are surprised at the sudden changes of
place, nor attend to our own existence, or identity; because our power of
volition is suspended. But all these circumstances are more or less
observable in our incomplete ones; for then we attend a little to the
lapse of time, and the changes of place, and to our own existence; and
even to our identity of person; for a lady seldom dreams, that she is a
soldier; nor a man, that he is brought to bed.

14. As long as our sensations only excite
their sensual motions, or ideas, our sleep continues sound; but as soon
as they excite desires or aversions, our sleep becomes imperfect; and
when that desire or aversion is so strong, as to produce voluntary
motions, we begin to awake; the larger muscles of the body are brought
into action to remove that irritation or sensation, which a continued
posture has caused; we stretch our limbs, and yawn, and our sleep is thus
broken by the accumulation of voluntary power.

Sometimes it happens, that the act of waking is suddenly produced, and
this soon after the commencement of sleep; which is occasioned by some
sensation so disagreeable, as instantaneously to excite the power of
volition; and a temporary action of all the voluntary motions suddenly
succeeds, and we start awake. This is sometimes accompanied with loud
noise in the ears, and with some degree of fear; and when it is in great
excess, so as to produce continued convulsive motions of those muscles,
which are generally subservient to volition, it becomes epilepsy: the
fits of which in some patients generally commence during sleep. This
differs from the night-mare described in No. 3. of this Section, because in that the
disagreeable sensation is not so great as to excite the power of volition
into action; for as soon as that happens, the disease ceases.

Another circumstance, which sometimes awakes people soon after the
commencement of their sleep, is where the voluntary power is already so
great in quantity as almost to prevent them from falling asleep, and then
a little accumulation of it soon again awakens them; this happens in
cases of insanity, or where the mind has been lately much agitated by
fear or anger. There is another circumstance in which sleep is likewise
of short duration, which arises from great debility, as after great
over-fatigue, and in some fevers, where the strength of the patient is
greatly diminished, as in these cases the pulse intermits or flutters,
and the respiration is previously affected, it seems to originate from
the want of some voluntary efforts to facilitate respiration, as when we
are awake. And is further treated of in Vol. II. Class I. 2. 1. 2. on the
Diseases of the Voluntary Power. Art. Somnus interruptus.

15. We come now to those motions which
depend on irritation. The motions of the arterial and glandular systems
continue in our sleep, proceeding slower indeed, but stronger and more
uniformly, than in our waking hours, when they are incommoded by external
stimuli, or by the movements of volition; the motions of the muscles
subservient to respiration continue to be stimulated into action, and the
other internal senses of hunger, thirst, and lust, are not only
occasionally excited in our sleep, but their irritative motions are
succeeded by their usual sensations, and make a part of the farrago of
our dreams. These sensations of the want of air, of hunger, thirst, and
lust, in our dreams, contribute to prove, that the nerves of the external
senses are also alive and excitable in our sleep; but as the stimuli of
external objects are either excluded from them by the darkness and
silence of the night, or their access to them is prevented by the
suspension of volition, these nerves of sense fall more readily into
their connexions with sensation and with association; because much
sensorial power, which during the day was expended in moving the external
organs of sense in consequence of irritation from external stimuli, or in
consequence of volition, becomes now in some degree accumulated, and
renders the internal or immediate organs of sense more easily excitable
by the other sensorial powers. Thus in respect to the eye, the irritation
from external stimuli, and the power of volition during our waking hours,
elevate the eye-lids, adapt the aperture of the iris to the quantity of
light, the focus of the crystalline humour, and the angle of the optic
axises to the distance of the object, all which perpetual activity during
the day expends much sensorial power, which is saved during our
sleep.

Hence it appears, that not only those parts of the system, which are
always excited by internal stimuli, as the stomach, intestinal canal,
bile-ducts, and the various glands, but the organs of sense also may be
more violently excited into action by the irritation from internal
stimuli, or by sensation, during our sleep than in our waking hours;
because during the suspension of volition, there is a greater quantity of
the spirit of animation to be expended by the other sensorial powers. On
this account our irritability to internal stimuli, and our sensibility to
pain or pleasure, is not only greater in sleep, but increases as our
sleep is prolonged. Whence digestion and secretion are performed better
in sleep, than in our waking hours, and our dreams in the morning have
greater variety and vivacity, as our sensibility increases, than at night
when we first lie down. And hence epileptic fits, which are always
occasioned by some disagreeable sensation, so frequently attack those,
who are subject to them, in their sleep; because at this time the system
is more excitable by painful sensation in consequence of internal
stimuli; and the power of volition is then suddenly exerted to relieve
this pain, as explained Sect. XXXIV. 1.
4.

There is a disease, which frequently affects children in the cradle,
which is termed ecstasy, and seems to consist in certain exertions to
relieve painful sensation, in which the voluntary power is not so far
excited as totally to awaken them, and yet is sufficient to remove the
disagreeable sensation, which excites it; in this case changing the
posture of the child frequently relieves it.

I have at this time under my care an elegant young man about
twenty-two years of age, who seldom sleeps more than an hour without
experiencing a convulsion fit; which ceases in about half a minute
without any subsequent stupor. Large doses of opium only prevented the
paroxysms, so long as they prevented him from sleeping by the
intoxication, which they induced. Other medicines had no effect on him.
He was gently awakened every half hour for one night, but without good
effect, as he soon slept again, and the fit returned at about the same
periods of time, for the accumulated sensorial power, which occasioned
the increased sensibility to pain, was not thus exhausted. This case
evinces, that the sensibility of the system to internal excitation
increases, as our sleep is prolonged; till the pain thus occasioned
produces voluntary exertion; which, when it is in its usual degree, only
awakens us; but when it is more violent, it occasions convulsions.

The cramp in the calf of the leg is another kind of convulsion, which
generally commences in sleep, occasioned by the continual increase of
irritability from internal stimuli, or of sensibility, during that state
of our existence. The cramp is a violent exertion to relieve pain,
generally either of the skin from cold, or of the bowels, as in some
diarrhœas, or from the muscles having been previously overstretched,
as in walking up or down steep hills. But in these convulsions of the
muscles, which form the calf of the leg, the contraction is so violent as
to occasion another pain in consequence of their own too violent
contraction; as soon as the original pain, which caused the contraction,
is removed. And hence the cramp, or spasm, of these muscles is continued
without intermission by this new pain, unlike the alternate convulsions
and remissions in epileptic fits. The reason, that the contraction of
these muscles of the calf of the leg is more violent during their
convulsion than that of others, depends on the weakness of their
antagonist muscles; for after these have been contracted in their usual
action, as at every step in walking, they are again extended, not, as
most other muscles are, by their antagonists, but by the weight of the
whole body on the balls of the toes; and that weight applied to great
mechanical advantage on the heel, that is, on the other end of the bone
of the foot, which thus acts as a lever.

Another disease, the periods of which generally commence during our
sleep, is the asthma. Whatever may be the remote cause of paroxysms of
asthma, the immediate cause of the convulsive respiration, whether in the
common asthma, or in what is termed the convulsive asthma, which are
perhaps only different degrees of the same disease, must be owing to
violent voluntary exertions to relieve pain, as in other convulsions; and
the increase of irritability to internal stimuli, or of sensibility,
during sleep must occasion them to commence at this time.

Debilitated people, who have been unfortunately accustomed to great
ingurgitation of spirituous potation, frequently part with a great
quantity of water during the night, but with not more than usual in the
day-time. This is owing to a beginning torpor of the absorbent system,
and precedes anasarca, which commences in the day, but is cured in the
night by the increase of the irritability of the absorbent system during
sleep, which thus imbibes from the cellular membrane the fluids, which
had been accumulated there during the day; though it is possible the
horizontal position of the body may contribute something to this purpose,
and also the greater irritability of some branches of the absorbent
vessels, which open their mouths in the cells of the cellular membrane,
than that of other branches.

As soon as a person begins to sleep, the irritability and sensibility
of the system begins to increase, owing to the suspension of volition and
the exclusion of external stimuli. Hence the actions of the vessels in
obedience to internal stimulation become stronger and more energetic,
though less frequent in respect to number. And as many of the secretions
are increased, so the heat of the system is gradually increased, and the
extremities of feeble people, which had been cold during the day, become
warm. Till towards morning many people become so warm, as to find it
necessary to throw off some of their bed-clothes, as soon as they awake;
and in others sweats are so liable to occur towards morning during their
sleep.

Thus those, who are not accustomed to sleep in the open air, are very
liable to take cold, if they happen to fall asleep on a garden bench, or
in a carriage with the window open. For as the system is warmer during
sleep, as above explained, if a current of cold air affects any part of
the body, a torpor of that part is more effectually produced, as when a
cold blast of air through a key-hole or casement falls upon a person in a
warm room. In those cases the affected part possesses less irritability
in respect to heat, from its having previously been exposed to a greater
stimulus of heat, as in the warm room, or during sleep; and hence, when
the stimulus of heat is diminished, a torpor is liable to ensue; that is,
we take cold. Hence people who sleep in the open air, generally feel
chilly both at the approach of sleep, and on their awaking; and hence
many people are perpetually subject to catarrhs if they sleep in a less
warm head-dress, than that which they wear in the day.

16. Not only the sensorial powers of
irritation and of sensation, but that of association also appear to act
with greater vigour during the suspension of volition in sleep. It will
be shewn in another place, that the gout generally first attacks the
liver, and that afterwards an inflammation of the ball of the great toe
commences by association, and that of the liver ceases. Now as this
change or metastasis of the activity of the system generally commences in
sleep, it follows, that these associations of motion exist with greater
energy at that time; that is, that the sensorial faculty of association,
like those of irritation and of sensation, becomes in some measure
accumulated during the suspension of volition.

Other associate tribes and trains of motions, as well as the
irritative and sensitive ones, appear to be increased in their activity
during the suspension of volition in sleep. As those which contribute to
circulate the blood, and to perform the various secretions; as well as
the associate tribes and trains of ideas, which contribute to furnish the
perpetual dreams of our dreaming imaginations.

In sleep the secretions have generally been supposed to be diminished,
as the expectorated mucus in coughs, the fluids discharged in
diarrhœas, and in salivation, except indeed the secretion of sweat,
which is often visibly increased. This error seems to have arisen from
attention to the excretions rather than to the secretions. For the
secretions, except that of sweat, are generally received into reservoirs,
as the urine into the bladder, and the mucus of the intestines and lungs
into their respective cavities; but these reservoirs do not exclude these
fluids immediately by their stimulus, but require at the same time some
voluntary efforts, and therefore permit them to remain during sleep. And
as they thus continue longer in those receptacles in our sleeping hours,
a greater part is absorbed from them, and the remainder becomes thicker,
and sometimes in less quantity, though at the time it was secreted the
fluid was in greater quantity than in our waking hours. Thus the urine is
higher coloured after long sleep; which shews that a greater quantity has
been secreted, and that more of the aqueous and saline part has been
reabsorbed, and the earthy part left in the bladder; hence thick urine in
fevers shews only a greater action of the vessels which secrete it in the
kidneys, and of those which absorb it from the bladder.

The same happens to the mucus expectorated in coughs, which is thus
thickened by absorption of its aqueous and saline parts; and the same of
the feces of the intestines. From hence it appears, and from what has
been said in No. 15. of this Section
concerning the increase of irritability and of sensibility during sleep,
that the secretions are in general rather increased than diminished
during these hours of our existence; and it is probable that nutrition is
almost entirely performed in sleep; and that young animals grow more at
this time than in their waking hours, as young plants have long since
been observed to grow more in the night, which is their time of
sleep.

17. Two other remarkable circumstances of
our dreaming ideas are their inconsistency, and the total absence of
surprise. Thus we seem to be present at more extraordinary metamorphoses
of animals or trees, than are to be met with in the fables of antiquity;
and appear to be transported from place to place, which seas divide, as
quickly as the changes of scenery are performed in a play-house; and yet
are not sensible of their inconsistency, nor in the least degree affected
with surprise.

We must consider this circumstance more minutely. In our waking trains
of ideas, those that are inconsistent with the usual order of nature, so
rarely have occurred to us, that their connexion is the slightest of all
others: hence, when a consistent train of ideas is exhausted, we attend
to the external stimuli, that usually surround us, rather than to any
inconsistent idea, which might otherwise present itself; and if an
inconsistent idea should intrude itself, we immediately compare it with
the preceding one, and voluntarily reject the train it would introduce;
this appears further in the Section on Reverie, in which state of the
mind external stimuli are not attended to, and yet the streams of ideas
are kept consistent by the efforts of volition. But as our faculty of
volition is suspended, and all external stimuli are excluded in sleep,
this slighter connexion of ideas takes place; and the train is said to be
inconsistent; that is, dissimilar to the usual order of nature.

But, when any consistent train of sensitive or voluntary ideas is
flowing along, if any external stimulus affects us so violently, as to
intrude irritative ideas forcibly into the mind, it disunites the former
train of ideas, and we are affected with surprise. These stimuli of
unusual energy or novelty not only disunite our common trains of ideas,
but the trains of muscular motions also, which have not been long
established by habit, and disturb those that have. Some people become
motionless by great surprise, the fits of hiccup and or ague have been
often removed by it, and it even affects the movements of the heart, and
arteries; but in our sleep, all external stimuli are excluded, and in
consequence no surprise can exist. See Section XVII. 3. 7.

18. We frequently awake with pleasure from
a dream, which has delighted us, without being able to recollect the
transactions of it; unless perhaps at a distance of time, some analogous
idea may introduce afresh this forgotten train: and in our waking
reveries we sometimes in a moment lose the train of thought, but continue
to feel the glow of pleasure, or the depression of spirits, it
occasioned: whilst at other times we can retrace with ease these
histories of our reveries and dreams.

The above explanation of surprise throws light upon this subject. When
we are suddenly awaked by any violent stimulus, the surprise totally
disunites the trains of our sleeping ideas from these of our waking ones;
but if we gradually awake, this does not happen; and we readily unravel
the preceding trains of imagination.

19. There are various degrees of surprise;
the more intent we are upon the train of ideas, which we are employed
about, the more violent must be the stimulus that interrupts them, and
the greater is the degree of surprise. I have observed dogs, who have
slept by the fire, and by their obscure barking and struggling have
appeared very intent on their prey, that shewed great surprise for a few
seconds after their awaking by looking eagerly around them; which they
did not do at other times of waking. And an intelligent friend of mine
has remarked, that his lady, who frequently speaks much and articulately
in her sleep, could never recollect her dreams in the morning, when this
happened to her: but that when she did not speak in her sleep, she could
always recollect them.

Hence, when our sensations act so strongly in sleep as to influence
the larger muscles, as in those, who talk or struggle in their dreams; or
in those, who are affected with complete reverie (as described in the
next Section), great surprise is produced, when they awake; and these as
well as those, who are completely drunk or delirious, totally forget
afterwards their imaginations at those times.

20. As the immediate cause of sleep
consists in the suspension of volition, it follows, that whatever
diminishes the general quantity of sensorial power, or derives it from
the faculty of volition, will constitute a remote cause of sleep; such as
fatigue from muscular or mental exertion, which diminishes the general
quantity of sensorial power; or an increase of the sensitive motions, as
by attending to soft music, which diverts the sensorial power from the
faculty of volition; or lastly, by increase of the irritative motions, as
by wine, or food; or warmth; which not only by their expenditure of
sensorial power diminish the quantity of volition; but also by their
producing pleasureable sensations (which occasion other muscular or
sensual motions in consequence), doubly decrease the voluntary power, and
thus more forcibly produce sleep. See Sect. XXXIV. 1. 4.

Another method of inducing sleep is delivered in a very ingenious work
lately published by Dr. Beddoes. Who, after lamenting that opium
frequently occasions restlessness, thinks, “that in most cases it would
be better to induce sleep by the abstraction of stimuli, than by
exhausting the excitability;” and adds, “upon this principle we could not
have a better soporific than an atmosphere with a diminished proportion
of oxygene air, and that common air might be admitted after the patient
was asleep.” (Observ. on Calculus, &c. by Dr. Beddoes, Murray.) If it
should be found to be true, that the excitability of the system depends
on the quantity of oxygene absorbed by the lungs in respiration according
to the theory of Dr. Beddoes, and of M. Girtanner, this idea of sleeping
in an atmosphere with less oxygene in its composition might be of great
service in epileptic cases, and in cramp, and even in fits of the asthma,
where their periods commence from the increase of irritability during
sleep.

Sleep is likewise said to be induced by mechanic pressure on the brain
in the cases of spina bifida. Where there has been a defect of one of the
vertebræ of the back, a tumour is protruded in consequence; and, whenever
this tumour has been compressed by the hand, sleep is said to be induced,
because the whole of the brain both within the head and spine becomes
compressed by the retrocession of the fluid within the tumour. But by
what means a compression of the brain induces sleep has not been
explained, but probably by diminishing the secretion of sensorial power,
and then the voluntary motions become suspended previously to the
irritative ones, as occurs in most dying persons.