ALL our knowledge is derived from comparing the relations and discrepancies which subsist between different objects.  If brute animals had no existence, the nature of man would be still more incomprehensible.  Having formerly considered man as a detached being, let us now institute a comparison between him and the other animals.  Let us examine the nature of the animal world; let us investigate their organization, and study their general oeconomy.  This inquiry will enable us to draw particular in- [208] ferences, to discover relations, to reconcile apparent differences, and, from a combination of facts, to distinguish the principal effects of the living machine, and lead us to that important science, of which man is the ultimate object.

            I shall begin with explaining the subject, and by reducing it to its just limits.

            The general properties of matter, being common to animated as well as inanimated beings, belong not to our subject.*  The qualities possessed by plants as well as animals, ought likewise  to be rejected.  It is for this reason that we have treated of nutrition, of growth, of reproduction, and even of generation, properties common to the plant and animal, before entering upon those qualities which are peculiar to, and constitute animated bodies.

            In the next place, as many beings are comprehended in the class of animals, whose organization differs greatly from that of man, and the more perfect animals, we shall likewise keep these out of our view, and examine such only as make the nearest approaches to ourselves.

            But, as man is not a simple animal, and as his nature is superior to that of other animals, we shall endeavour to investigate the cause of this superiority, in order that we may be enabled to distinguish what is peculiar to him, from what he possesses in common with other animated beings.  [209]

            Having thus circumscribed our subject, and lopt [sic] off its extremities, we shall proceed to the general division of it.  Before giving a detail of the various parts, and of their functions, let us attend to the general results of the animal machine; and, before reasoning upon the causes, let us enumerate and describe the effects.

            An animal is distinguished by two modes of existence, that of motion, and that of rest, which alternately succeed one another during the whole of life.  In the former, all the springs of the machine are in action; in the latter, al is at rest, excepting one part, and that part acts equally when the animal is asleep and when it is awake.  This part, therefore, is absolutely necessary, since the animal cannot exist in any manner without it.  This part is likewise independent of the other, because it can act alone; and the other part depends upon this, because it cannot act without its assistance.  The one is a fundamental part of the animal oeconomy, because it acts continually, and without interruption; the other is less essential, because it acts only be alternate intervals.

            This first division of the animal oeconomy is general, and seems to be well founded.  It is not so difficult to examine an animal when asleep, as when awake and in action.  This distinction is essential, and not a simple change of condition, as in an inanimated body, which is equally indifferent to rest or motion; for an inanimated body would continue perpetually in [210] either of these states, unless it were constrained to change, by the application of some impelling or resisting force.  But an animal changes its state by its own proper powers.  It passes naturally, and without restraint, from motion to rest, and from rest to motion.  The moment of awaking returns as necessarily as that of sleep, and both happen independent of foreign causes; because the animal can exist during a certain time only in either state; and continued walking or sleeping would be equally fatal to life.

            The animal oeconomy, then, may be divided into two parts; the first of which acts perpetually without any interruption, and the second acts by intervals only.  The action of the heart and lungs, in animals which respire, and the action of the heart in the foetus state, constitute the former; and the action of the senses, joined to the movements of the members, constitute the latter.

            If we conceive the existence of beings endowed by Nature with this first part of the animal oeconomy only, though deprived of sense and progressive motion, they would still be animated, and would differ in nothing from animals asleep.  An oyster, or a zoophyte, which appear not to possess either external senses, or the power of progressive motion, are animals destined to sleep continually.  A vegetable, in this view, is a sleeping animal:  And, in general, every organized being, deprived of sense and motion, may [211] be compared to an animal constrained by Nature to perpetual sleep.

            Sleep, in the animal, therefore, is not an accidental state induced by the exercise of its functions while awake:  It is, on the contrary, an essential mode of existence, and serves as a basis to the animal oeconomy.  Our being commences with sleep; the foetus sleeps perpetually; and the infant consumes most of its time in that state.

            Sleep, therefore, which appears to be a state purely passive, a species of death, is, on the contrary, the original condition of animated beings, and the very foundation of life itself.  It is not a privation of certain qualities and exertions, but a real and more general mode of existence than any other.  With sleep our existence commences:  All organized beings, which are not endowed with senses, remain perpetually in this condition; none exist in continued action; and the existence of every animal consists more or less of this state of repose.

            If the most perfect animal were reduced to that part alone which acts perpetually, it would not differ, in appearance, from those beings to which we can hardly ascribe the name of Animal.  With regard to external functions, it would have a striking resemblance to a vegetable; for, though the animal and vegetable differ in external organization, they both exhibit the same results:  they both receive nourishment, [212] grow, expand, and are endowed with internal movements and a vegetating life.  On this supposition, they would be equally deprived of progressive motion, action, and sentiment; and they would have no external or apparent character of animation.  But, if this internal part be clothed with a proper cover, or, in other words, if it be endowed with senses and members, animal life will instantly manifest itself; and, in proportion to the quantity of sense and members contained in this cover, the animation will be more complete, and the animal more perfect.  It is this envelope or cover, therefore, which constitutes the distinction between different animals.  The internal part, which is the basis of the animal oeconomy, is common to every animated being, without exception; and, as to its mode, it is nearly the same in man and in all animals which consist of flesh and blood.  But the external cover is exceedingly diversified, and the greatest differences originate from the extremities of this cover.

            To illustrate this subject, let us compare the body of a man with that of a horse, an ox, &c.  The internal part, which acts perpetually, namely the heart and lungs, or the organs of circulation and respiration, is nearly the same in man and in the animal.  But the external cover is extremely different.  The solids of the animal’s body, though composed of parts similar to those of the human frame, differ prodigiously in [213] number, magnitude, and position.  The bones are more or less shortened, rounded, lengthened, flattened, &c.  Their extremities are more or less elevated, or hollowed; and several of them are sometimes united into one.  Some, as the clavicles, are entirely wanting; the number of others is augmented, as the cartilages of the nose, the vertebrae, the ribs, &c.  Of others, the number is diminished, as the bones of the carpus, metacarpus, tarsus, metatarsus, phalanges, &c. which give rise to great varieties in the figure of animals, compared with that of the human body.

            We will be still farther convinced, that the principal distinctions between the body of man, and those of the other animals, arise from the extremities, it we attend to the following circumstances.  Let us divide the body into three principal parts, the trunk, the head, and the members.  The head and members, which are the extremities of the body, constitute the chief differences between man and the other animals.  By examining these three principal parts, we find that the greatest differences in the trunk are found at its superior and inferior extremities; for the animals have no clavicles on the superior extremity of the trunk, and the inferior is terminated by a tail, which consists of a certain number of external vertebrae, which exist not in man.  In the same manner, the inferior extremity of the head, or jaw-bones, and the superior, [214] or frontal bone, differ widely in man and the quadrupeds:  The jaw-bones of most animals are greatly lengthened, and their frontal bones, on the contrary are contracted.  In fine, by comparing the members of a brute with those of a man, it is easy to perceive that they differ chiefly in their extremities; for, at the first glance of the eye, nothing has less resemblance to the human hand, than the foot of a horse or an ox.

            Regarding the heart, therefore, as the centre of the animal machine, it is obvious that man resembles the other animals in this and the neighbouring parts; and that the farther from this centre, the differences become more considerable, till we arrive at the exgtremities, where they are by much the greatest.  But, where this centre, or the heart itself, differs, then the animal is infinitely removed from man, and possesses nothing in common with the creatures under consideration.  In most insects, for example, the organization of this principal part of the animal oeconomy is singular.  Instead of a heart and lungs, we find parts which perform similar functions, and for that reason have been regarded as analogous to those viscera, but which, in reality, are very different, both in their structure, and in the result of their action.  A slight variation in the central parts is always accompanied with an amazing differ- [215] ence in the external configuration.  The heart of a turtle is of a singular structure; and its figure is so extraordinary, that it has no resemblance to any other creature.

            In contemplating men, quadrupeds, birds, fishes, and reptiles, what a prodigious variety occurs in the figure and proportion of their bodies, in the number and position of their members, in the substance of their flesh, bones, and integuments?  The quadrupeds have tails and horns; and all their extremities differ remarkably from those of man.  The cetaceous animals live in a different element; and, though they generate in a manner similar to the quadrupeds, their figure is extremely different, being totally deprived of interior extremities.  The birds differ still more from man, by their beak, their feathers, their flying, and their multiplication by means of eggs.  The fishes and amphibious animals are still farther removed from the human figure; and the reptiles are entirely destitute of members.  Thus we find, that the greatest diversity consists in the envelope or external cover, the internal structure, on the contrary, being nearly the same:  All animals are furnished with a heart, a liver, a stomach, intestines, and organs of generation.  These, therefore, ought to be regarded as the most essential parts of the animal oeconomy, because they are the most constant, and least subjected to variation.  [216]

            But it is worthy of remark, that, even in this cover, some parts are more constant than others.  None of these animals are deprived of all the senses.  In treating of the sense, we explained what might be their species of feeling.  We know not the nature of their smelling and taste; but we are certain, that they are all endowed with the sense of seeing, and perhaps also with that of hearing.  The senses, therefore, may be considered as another essential part of the animal oeconomy, as well as the brain, which is the origin of all sensation.  Even the insects, which differ so much in their central parts from other animals, have something analogous to a brain, and its functions are similar to those of the other animals:  And those animals, as the oister, which seem to be deprived of a brain, ought to be regarded as beings only half animated, and as forming the shade between animal and vegetable life.

            Thus we have discovered the brain and the senses to be a second essential part of the animal oeconomy.  The brain is the centre of the envelope or cover, as the heart is the centre of the internal part of the animal.  It is from the brain that the external parts receive their power of moving and acting, by means of the spinal marrow and the nerves, which are only prolongations of this marrow:  And, as the heart and the whole interior parts communicate with the brain and ex- [217] ternal cover, by means of the distribution of blood-vessels, the brain has a similar communication with the internal parts by the ramification of the nerves.  This union is intimate and reciprocal; and, though the functions of the two organs be totally different, they cannot be separated, without instant destruction to the animal.

            The heart, and the whole interior parts, act continually, without the smallest interruption, and independent of external causes.  But the senses and envelope act only by alternate intervals, and successive vibrations excited by external causes.  Objects act upon the senses, and this action is modified by the senses, and transported, in this modified form, to the brain, where the impression first receives the appellation of Sensation:  The brain, in consequence of this impression, acts upon the nerves, and communicates the vibrations it receives; and these vibrations produce progressive motion, and all the other external actions of the body.  When a body is acted upon by any cause, it is well known, that the body re-acts upon the cause.  Thus objects act upon animals by means of the senses, and animals re-act upon objects by their external movements; and, in general, action is the cause, and re-action the effect.

            The effect, it may be said, is not, in this case, proportioned to the cause:  In solid bodies, which follow the laws of mechanism, action and reaction are always equal.  But, in the animal [218] body, re-action, or external motion, seems to be incomparably greater than action; and, consequently, progressive motion, and the other external movements, ought not to be regarded as simple effects of the impressions of objects upon the senses.  To this objection I reply, that, though effects, in certain circumstances, appear to be proportioned to their cause; yet there are in nature innumerable instances where the effects have no proportion to their apparent causes.  A single spark of fire will inflame a magazine of powder, and blow up a citadel.  A slight friction produces, by electricity, a concussion so violent, that it is communicated to great distances, and affects equally a thousand persons at the same time.  It is not, therefore, surprising that a slight impression on the sense should produce a violent re-action in the animal body, manifesting itself by external movements.

            Causes which admit of measurement, and the quantity of whole effects can be exactly estimated, are not so numerous as those whose qualities and manner of acting are perfectly unknown; and, consequently, the proportion they may have to their effects must be equally unknown.  To measure a cause, it must be simple; its action must be constant, and uniformly the same, or, at least, it must vary only according to a known law.  Now, most effects in nature are produced by a combination of different causes, the action of which varies, and which observe no constant [219] law; and, of course, they can neither be measured, nor estimated, but by endeavouring to approach the truth by probable conjectures. 

            I pretend not, therefore, to lay it down as a demonstrated fact, that progressive motion, and the other external movements of animals, have no other cause but that of the impressions of objects upon the senses.  I only say, that the fact is probable, and seems to be founded on strong analogies:  For I find, that all organized beings, which are deprived of senses, are likewise deprived of the power of progressive motion, and that all those which are endowed with senses, enjoy likewise the loco-motive faculty.  I also find, that this action of objects upon the senses often makes the animal move instantaneously, and even involuntarily; and that, when the movement is determined by the will, it is always the effect either of the immediate action of objects upon the senses, or of the remembrance of a former impression.

            To render this matter more clear, let us analyze the physical laws of our own actions.  When an object strikes any of our senses, and produces an agreeable sensation, and, of course, a desire, this desire must have a relation to some quality or mode of our enjoyment.  We cannot desire an object in any other way than to have an inclination to see, hear, taste, smell, or touch it; and this desire is only to gratify more fully either that sense with which we perceive the object, or some [220] of our other senses at the same time; or, in other words, to heighten the agreeableness of the first sensation, or to excite another, which is a new mode of enjoying an object:  For, the moment we perceive our object, if we could fully enjoy it by all the senses at once, we would have nothing to desire.  Desire, then, originates from our being ill situated with regard to the object perceived.  We are either too near or too distant from it.  We, therefore, naturally change our situation; because, at the same time that we perceive the object, we also perceive the obstruction to the full enjoyment of it, arising from the distance or proximity of our situation.  Hence the movements we perform in consequence of desire, and the desire itself, proceed entirely from the impression made by the object upon our senses.

            When we perceive an object with the eye, and have an inclination to touch it, if it be near, we seize it with our hand, and, if at a distance, we move forward in order to approach it.  A man, when deeply occupied with study, if he be hungry, will lay hold of bread which he feels under his hand, and even carry it to his mouth and eat it, without being conscious of his having acted in this manner. These motions necessarily result from the first impression made by the object; and they would never fail to succeed the impression, if this natural effect were not opposed by other impressions, which, by acting at the [221] same time, often weaken and efface the action of the first.

            An organized being, therefore, without sensation, as an oyster, which probably enjoys the sense of feeling very imperfectly, is deprived not only of progressive motion, but of sentiment and intelligence; because each of them would be equally excite desire, and this desire would manifest itself by external movements.  I am uncertain whether beings deprived of senses have any perception of their own existence; if they have, it must be very imperfect, since they are unable to perceive the existence of others.

            To illustrate this subject still farther, let us suppose a man, at the moment he wishes to approach an object, suddenly deprived of all his members, would he not endeavour to trail his trunk along the ground in order to gratify his desire?  Nay, were he reduced to a globular form, and actuated by the same desires, though deprived of every faculty of motion, he would still exert al lhis force to obtain a change of situation:  But, on this supposition, as he could only act against the point that supported him, he would still evince his passion by raising his body.  Thus external and progressive motion depend not on the organization and figure of the body, since, whatever be the confirmation of any being, if endowed with senses and a desire of gratifying them, it would not fail to move.  [222]

The facility, the quickness, the direction, and the continuation of motion, depend, it is true, upon external organization:  But the cause, principle, and determination of it, proceed solely from desire, excited by the impression of objects upon the sense; for, if a man were deprived of sight, he would make no movement to gratify his eyes.  The same thing would happen if he were deprived of any of the other senses; and, if deprived of every sense, he would remain perpetually at rest; and no object would excite him to move, though, by his external conformation, he were fully capable of motion.

Natural wants, as that of taking nourishment, are internal movements, which necessarily excite desire or appetite.  These movements may produce external motion in animals; and, provided they are not entirely deprived of external sense, relative to these wants, they will act in order to supply them.  Want is not desire; the former differs from the latter as cause differs from effect; desire, therefore, cannot be produced without the intervention of senses.  Whenever an animal perceives an object fitted to supply its wants, desire is instantly excited, and action or motion succeeds.

The action of external objects must necessarily produce some effect; and it is easy to perceive that this effect is animal motion, since every time the senses are struck in the same manner, the same movements uniformly succeed.  But how [223] does the action of objects excite desire or aversion?  How shall we obtain a clear conception of the operation of that principle to which the senses communicate their notices?  The senses are only the middle term between the action of objects and animal action.  This principle, however, has the power of determining all our motions; for it can modify and alter the animal action, and even sometimes counteract it, notwithstanding the impression of objects.

With regard to man, whose nature is so different from that of other animals, this question is difficult to solve; because the soul participates all our movements; and it is not easy to distinguish the effects of this spiritual substance from those produced solely by the material part of our frame.  Of this we can form no judgment but by analogy, and by comparing our actions to the natural operations of the other animals.  But, as this spiritual substance has been conferred on man alone, by which he is enabled to think and reflect, and, as the brutes are purely material, and neither think nor reflect, and yet act, and seem to be determined by motives, we cannot hesitate in pronouncing the principle of motion in them to be perfectly mechanical, and to depend absolutely on their organization.

            I apprehend, therefore, that, in the animal, the action of objects on the sense produces another on the brain, which I consider as a general internal sense, that receives all the impres- [224] sions to it by the external senses.  This internal sense is not only susceptible of vib rations from the action of the senses, but is capable of retaining, for a long time, the vibrations thus excited; and it is the continuation of these vibrations that constitute impressions, which are more or less deep, in proportion to the duration of the vibrations.

            The internal sense, therefore, differs, in the first place, from the external senses by the faculty which it possesses of receiving every species of impression; while the external senses are only affected in one mode, corresponding to their conformation:  The eye, for instance, is not more affected with sound than the ear with light.  2dly, The internal sense differs from the external senses, by the duration of the vibrations excited by external causes.  In every other article, both these species of senses are of the same nature.  The internal sense of a brute, as well as its external senses, are pure results of matter and mechanical organization.  Like the animal, man possesses this internal material sense; but he is likewise endowed with a sense of a very different and superior nature, residing in that spiritual substance which animates us, and superintends our determinations.

            Hence the brain of an animal is a general sense, which receives all impressions transmitted to it by the external senses; and these impressions or vibrations continue longer in the internal [225] than the external senses.  Of this we may easily form a conception, since the duration of impressions, even on the external senses, is very different.  The impression of light on the eye is well known to last much longer than that of sound on the ear.  A rapid succession of sounds can be heard distinctly; but a succession of colours equally rapid confounds the eye.  It is for this reason that the vibrations transmitted to the internal sense by the eye are stronger than those conveyed by the ear, and that we describe objects which we have seen in a more lively manner that those we have heard.  The vibrations excited by objects on the eye seem to continue longer than those made upon any of the other senses; and, therefore, it appears to participate more of the nature of the internal sense.  This might be proved by the quantity of nerves expanded on the eye; for it alone receives nearly as many as the three organs of hearing, smelling, and tasting.

            The eye, therefore, may be regarded as a continuation of the internal sense.  It consists, as was remarked in another place, almost entirely of nervous fibres, and is only a prolongation of the organ in which the internal sense resides.  It is not, of course, surprising that it should make the nearest approach to this internal sense.  Its impressions are not only more durable, but, like the internal sense, it possesses [226] powers of a nature superior to those of the other senses.

            The eye exhibits external marks of internal impressions.  It expresses desire or aversion excited by agreeable or disagreeable objects.  Like the internal sense, it is active; but all the other senses are purely passive:  They are simple organs, destined for the reception of external impressions, but incapable of preserving or reflecting them.

            When any of the senses, it must be allowed, are long and strongly acted upon, the vibrations continue some time after the action of the object has ceased.  But the eye possesses this power in a supereminent degree; and it is only exceeded by the brain, which not only preserves the impressions received, but propagates their action by communicating vibrations to the nerves.  The external organs of sense, the brain, the spinal marrow, and the nerves, which are expanded over the whole body, ought to be regarded as one continued mass, as an organic machine, of which the senses are the parts to which the action of external objects is applied.  The brain is the fulcrum or basis; and the nerves are the parts which receive motion from the acting powers.  But what renders this machine different from all others is, that its fulcrum not only resists and re-acts, but is even active itself; because it long retains received impressions. And, as this internal sense, the brain and its mem- [227] branes is very large, and endowed with great sensibility, it can admit many successive and contemporary vibrations, and retain them in the same order they were received; because each impression communicates vibrations to one part only of the brain, and successive impressions affect the same part, or contiguous parts, in a different manner.

            If we suppose an animal deprived of a brain, but endowed with an external sense of great extent and sensibility, as an eye, for example, having a retina as large as the brain, and possessing the faculty of retaining received impressions; it is certain, that an animal of this kind would see, at the same time, both present objects, and those which it had formerly seen; because, on this supposition, the vibrations always remaining, and the extent of the retina being large enough to receive them on different parts, the animal would perceive, at the same time, both present and past objects; and would, therefore, be mechanically determined to act according to the number or force of the vibrations produced by the images, corresponding with, or opposite to this determination.  If the number of images fitted to excite desire surpassed those suited to produce aversion, the animal would necessarily be determined to move, in order to gratify this appetite:  But, if the number and force of different images were equal, the animal, having no superior motive, would remain at rest.  I say, that all this [228] would happen mechanically, and without the intervention of memory; for, by seeing and being acted upon by all the images at the same time, those which correspond with desire would be opposed by those that correspond with aversion, and from this equilibrium, or from the excess in number or force of one set of images above another, the animal could alone be determined to rest or to action.

            From these facts it appears, that, in brutes, the internal sense differs only from the external senses, by the faculty it possesses of retaining received impressions.  This faculty is alone sufficient to explain all the actions of animals, and to give us some idea of what passes within them.  It likewise demonstrates the essential and infinite difference between them and us, and, at the same time, enables us to distinguish what we possess in common with them.

            Animals have some sense of exquisite acuteness; but, in general, they are not equal to those of man:  And, it is worthy of remark, that the degrees of excellence in the senses follow not the same order in the brute, as in the human species.  The sense most analogous to thinking is that of touch; and this sense is more perfect in man than in other animals. The sense of smelling is most analogous to instinct and appetite; and the brute enjoys it in a superior degree.  Hence man should excell [sic] in knowledge, and the brute in appetite.  In man, the [229] first sense for excellence is touching, and smelling is the last:  In the brute, the sense of smelling is the first, and that of touching is the last.  This difference has a perfect correspondence to the nature of each.  The sense of seeing is exceeding imperfect and delusive, without the aid of that of touching; and the former, accordingly, is less perfect in the brute than in man.  The ear, though perhaps equally well constructed in the animals as in man, is not nearly so useful to them, because they are deprived of speech, which, in man, depends on the ear, an organ which gives activity to this sense, and enables him to communicate his ideas:  But hearing, in the brute, is a sense almost entirely passive.  Hence man enjoys the senses of touching, seeing, and hearing, more perfectly, and that of smelling more imperfectly, than the animal; and, as taste is an internal smelling, and is more analogous to appetite than any of the other sense, the animals also possess it in superior degree, as appears from their invincible aversion against certain aliments, and their natural appetite for such as correspond to their constitutions:  But man, if he were not instructed, would eat the fruit of the manicella like an apple, and the hemlock like parsley.

            The excellence of the senses is the gift of nature; but art and habit may bestow on them a great degree of perfection.  A musician, whose ear is accustomed to harmony, is shocked with [230] discord :  A painter, with one glance of his eye, perceives a number of shades which escape a common observer.  The senses and even the appetites of animals may also be improved.  Some birds learn to sing, and to repeat words; and the ardor of a dog for the chace [sic] may be increased by rewarding him for his labours.

            But this excellence and improvement of the senses are most conspicuous in the brute, who always appears to be more active and intelligent in proportion to the perfection of his senses.  Man, on the contrary, has too great a portion of reason and genius to bestow much attention to the improvement of his ear or his eye.  Persons who are short-sighted, dull of hearing, or insensible of smell, suffer not, for that reason, any diminution of capacity:  An evident proof that man is endowed with something superior to an internal animal sense, which is a material organ, similar to the external organs of sensation, and differs from them only by the faculty of retaining received impressions.  But the soul of man is a superior sense, or spiritual substance, totally different, both in its action and essence, from the nature of the external senses.

            We mean not, however, to maintain that man is not possessed of an internal material sense, analogous to the external senses.  Inspection alone is sufficient to establish this point.  In man, the brain is proportionally larger than in any other animal, which is an evident proof of his [231] being endowed with this internal material sense.  What I mean to inculcate, is, that this sense is infinitely superior to the other.  It is subject to the commands of the spiritual substance, which, at pleasure, suppresses, or gives rise to all its operations.  In the animals, this sense is the principle which determines all its movements; but, in man, it is only an intermediate and secondary cause of action.

            But, let us examine more closely the powers of this internal material sense.  When we have once fixed the extent of its action, every thing beyond this limit must, of necessity, originate from the spiritual sense, and we will be furnished with a criterion for distinguishing what we possess in common with the other animals, and in what articles we excell [sic] them.

            The internal material sense receives indifferently every impression conveyed by the external senses.  These impressions proceed from the action of objects, and quickly pass through the external senses, where they only excite momentary vibrations.  But their progress stops at the brain, and produce, in this organ of the internal sense, vibrations which are both distinct and durable.  These vibrations give rise to desire or aversion, according to the present state and disposition of the animal.  Immediately after birth, the young animal begins to respire, and to feel a desire for food.  The organ of smelling receives the effluvia of the milk contained in the dugs of the [232] mother. Vibrations are excited in this sense by the odorous particles, and these vibrations are transmitted to the brain, which, in turn, acts upon the nerves; and the animal is thus stimulated to make the proper movements, or, in other words, to open its mouth, in order to procure the nourishment desired.  The senses peculiar to appetite being more obtuse in man than in the brutes, the new-born child feels only the desire of taking nourishment, which he announces by crying. But he is incapable of procuring it himself; neither is he stimulated by the sense of smelling; his mouth must be applied to the breat, before he can use the means of gratifying his appetite.  Then, indeed, the senses of smelling and of touching communicate vibrations to the brain, which, by re-acting on the nerves, stimulates the child to make the necessary motions for receiving and sucking the milk.  It is only by the senses of appetite, namely, those of smelling or tasting, that the brute animal is apprised of the presence of nourishment, or of the pace where it is to be found.  Its eyes are not yet open; and, though they were, they would not, at first, be capable of determining it to use the proper efforts.  The eye, which is a sense more analogous to intelligence than to appetite, is open in man from the moment of birth; but remains shut, in most other animals, for several days.  The senses of appetite, on the contrary, are more perfect and mature in the young [233] animal than in the infant. This affords another proof, that, in man, the organs of appetite are less perfect than those of intelligence; and that, in the animal, the organs of intelligence are more imperfect than those of appetite.

            The same remark may be made with regard to progressive motion, and all the other external movements.  It is long before the infant can use its members, or has strength enough to change place.  But a young animal soon acquires these faculties.  These powers, in the animal, are all relative to appetite, which is vehement, quickly unfolded, and the sole principle of motion.  But appetite, in man, is feeble, long before it is unfolded, and ought not to have such influence, as intelligence, upon the determination of his movements.  Man, therefore, is, in this respect, later in arriving at maturity.

            Hence, every circumstance, even in physics, concurs in demonstrating that the brutes are actuated by appetite only, and that man is influenced by a superior principle.  The only doubt that remains is the difficulty of conceiving how appetite alone should produce, in animals, effects so similar to those produced in men by intelligence; and how to distinguish the actions we perform in consequence of our intellectual powers, from those which originate from the force of appetite.  I despair not, however, of being able to remove this difficulty.  [234]

            The internal material sense, as formerly remarked, retains, for a long time, the vibrations it receives.  This sense, the organ of which is the brain, is common to every animal, and receives impressions transmitted to it by each of the external senses.  When an object acts upon the senses, this action produces lasting vibrations in the internal sense, and these vibrations communicate motion to the animal.  When the impression proceeds from the senses of appetite, the movements is determined, the animal either  advances to lay hold of the object, or flies to avoid it.  This motion may be uncertain, when the impression is transmitted by the senses analogous to intelligence, as the eye, and the ear.  When an animal sees or hears for the first time, he feels the impression of light or of sound; but the motions produced must be uncertain, because these senses have no relation to appetite.  It is only by repeated acts, and after the animal has joined to the impressions of seeing or hearing those of smelling, tasting, or touching, that he feels a determination to approach or retire from objects which experience alone renders analogous to his appetite.

            To illustrate this subject, let us examine the conduct of an animal that has been instructed by man.  A dog, for example, though excited by the most violent appetite, will not venture to wrest, from the hand of his master, the object that would gratify him; but he, at the same time, [235] makes a number of movements in order to obtain it.  Does not the dog, in this case, seem to combine ideas?  Does he not appear to desire, and to fear, in a word, to reason nearly in the same manner as a man, when violently tempted to take what belong to another, but is retrained by the fear of punishment?  This is the vulgar mode of accounting for the conduct of animals.  We naturally transfer our own motives to animals, when placed in similar circumstances; and the analogy is said to be well founded, because in man, and in the animal, the conformation of both the internal and external senses is similar.  Though this analogy, however, were just, is not something more required?  Is it not necessary that the animals should, on some occasions, do every thing which we perform?  But the contrary is evident:  Animals never invent, nor bring any thing to perfection; of course, they have no reflection; they uniformly do the same things in the same manner.  This destroys the force of the analogy so much, that we may even doubt of its reality:  We ought, therefore, to inquire, whether the actions of brutes proceed not from principles entirely different from those which actuate men, and whether their senses alone are not sufficient to produce their actions, without the necessity of ascribing to them the powers of reflection.

            Their internal sense is strongly agitated by every thing that relates to their appetites.  A [236] dog would instantly seize the object he desires, if his internal sense retained not impressions of pain, that had formerly accompanied this action.  But the animal has received new qualities from external impressions:  This prey is not presented to a simple dog, but to a dog that has been beat:  Every time he implicitly obeyed the dictates of appetite, has been followed with blows:  The impressions of pain, therefore, uniformly accompany those of appetite, because they have always been made at the same time.  The animal being thus acted upon at once by two contrary impulses, which mutually destroy each other, he remains in equilibrio [sic], between two equal powers.  The cause determining him to motion being counterbalanced, he makes no effort to obtain the object of his desire.  But, though the vibrations occasioned by appetite and aversion, or by pleasure and pain, destroy the effects of each other, a third vibration, which always accompanies the other two, is renewed in the brain of the animal, by the action of his master, from whose hand he has often received his food: And, as this third vibration is not counterbalanced by any opposite power, it becomes a cause sufficient to excite motion.  The dog is, therefore, determined to move towards his master, and to frisk about till his appetite be fully gratified.

            In the same manner, and upon the same principles, may all the actions of animals, however complicated they appear, be explained, without [237] the necessity of attributing to them either thought or reflection.  Their internal sense is sufficient to produce every motion they perform.  One thing only remains to be illustrated, and that is the nature of their sensations, which, according to the present doctrine, must be very different from ours. Have the animals, it may be asked, no knowledge, no sentiment, or no consciousness of their existence?  Since you pretend to explain all their actions by mechanism, do you not reduce them to mere machines, or insensible automatons?

            If I have properly explained myself, the reader ought to perceive, that, so far from depriving animals of all powers, I have already allowed them the possession of every thing but thought and reflection.  Their feelings are even more exquisite than ours.  They are conscious of their actual or present existence; but they have no knowledge of that existence which is past.  They have sensations; but they want the faculty of comparing them, or of forming ideas; for ideas are only the results of the association or comparison of sensations.

            Let us consider each of these articles separately.  The feelings of animals are more exquisite than those of man.  This, I imagine, has already been sufficiently proved by what was remarked concerning the excellence of their senses relative to appetite; by their natural and invincible aversion against certain objects, and their [238] uniform and determined attachment to others; and by the faculty of instantly distinguishing with certainty what is salutary or noxious.  Animals, therefore, as well as men, are capable of pleasure and pain.  They have no knowledge of good and evil; but they feel the distinction.  Whatever is agreeable to them is good, and whatever is disagreeable is bad.  Both are only relations comformable [sic] or repugnant to their nature and organization.  The pleasure of tickling, and the pain of an wound [sic], are common to us and the animals; because they depend absolutely upon an external material cause, namely, a weaker or stronger action in the nerves, which are the organs of sensation.  Every thing that acts gently on these organs gives pleasure; and every thing that acts with violence is the cause of pain.  All sensations, then, are sources of pleasure, when they are temperate and natural; but, when too violent, they produce pain, which, in physics, is the extreme, rather than the opposite of pleasure.

            Disagreeable sensations are excited by a light too brilliant, too near an approach to fire, loud noises, strong smells, insipid or coarse victuals, and hard friction.  But a gentle light, a moderate heat, a soft sound, a delicate perfume, a fine savour [sic], and slight friction, produce sensations of the most agreeable kind.  Thus every gentle application to the senses is pleasure, and every shock, or violent impression, is pain.  As the [239] causes, therefore, which give rise to violent impressions, occur more seldom in nature than those that produce soft and moderate movements; and as animals, by the exercise of their senses, soon acquire the habit of avoiding hurtful objects, and of distinguishing and approaching such as are agreeable to them, the sum of agreeable sensations must exceed that of the disagreeable; and therefore the quantity of pleasure must be greater than that of pain.

            If animal pleasure consists of whatever flatters the senses, and if, in physics, what flatters the senses be every thing that corresponds to nature; if, on the other hand, pain be whatever wounds the organs, and is repugnant to nature; if, in a word, pleasure be physical good, and pain physical evil, it is evident, that every sentient being must enjoy more pleasure than pain; for every thing that corresponds with his nature, contributes to his preservation, or supports his existence, is pleasant; and every thing that tends to his destruction, to derange his organization, or to change his natural condition, is pain.  It is by pleasure alone, therefore, that a sentient being can continue to exist; and, if the sum of agreeable sensations surpassed not that of the disagreeable, deprived of pleasure, he would first languish for want of good, and, loaded with pain, he would next perish by a superabundance of evil.  [240]

            In man, physical good and evil constitute the smallest part of his pleasures and pains.  His imagination, which is never idle, is a constant source of unhappiness; for it presents to the mind nothing but vain phantoms, or exaggerated pictures.  More occupied by these illusions than by real objects, the mind loses both its faculty of judging and its empire:  It compares chimeras only; it sees only at second hand, and often sees impossibilities.  The will, of which the mind has now no command, becomes a burden:  In fine, his extravagant desires are real pains, and his vain hopes are at most but false pleasures, which vanish as soon as the mind resumes its faculty of discerning and of judging without passion.

            Thus, when we search for pleasure, we create to ourselves pain; we are miserable from the moment we desire to augment our happiness.  Good exists only within ourselves, and it has been bestowed on us by Nature; evil is external, and we go in quest of it.  The peaceable enjoyment of the mind is our only true good:  We cannot augment this good, without the danger of losing it:  The less we desire, the more we possess:  Whatever we wish beyond what Nature has bestowed on us is pain; and nothing is pleasure but what she offers us.

            Now, pleasures innumerable are constantly presented to us by Nature:  She has provided for our wants, and fortified us against pain:  Physi- [241] cal good infinitely exceeds physical evil.  It is not, therefore, realities, but chimeras, which we ought to dread.  Neither bodily pain, nor disease, nor death, are formidable; but agitation of mind, the passions, and languor, are the only evils we have to apprehend.

            The animals have only one mode of acquiring pleasure, the exercise of their sensations to gratify their desires.  We also possess this faculty:  But we are endowed with another source of pleasure, the exercise of the mind, the appetite of which is the desire of knowledge.  This source of pleasure would be more pure and copious, were its current not interrupted by our passions, which destroy all contemplation.  Whenever they obtain the ascendant, reason is silenced, or only makes feeble and unavailing efforts.  We, of course, lose all relish of truth; the charm of illusion augments; error fortifies its dominion, and drags us on to misery:  For what misery can be greater than no longer to see things as they are, to have the faculty of judging perverted by passion, to act only according to its dictates, to appear, consequently, unjust or ridiculous to others, and, lastly, to be obliged to despise ourselves, whenever we can command a moment’s reflection?

            In this state of darkness and illusion, we would willingly change the nature of the soul; she has been bestowed on us for the purposes of knowledge, and we would employ her only for those [242] of sensation.  If we could extinguish her light entirely, instead of regretting the loss, we would envy the condition of idiots.  As we only reason by intervals, and as these intervals are burdensome to us, and pass in secret reproaches, we wish to suppress them.  Thus, proceeding always from illusion to illusion, voluntarily seek to lose sight of ourselves, and to terminate the whole by forgetting our existence.

            Uninterrupted passion is madness; and madness is the death of the soul.  Violent passions, with intervals, are paroxysms of folly, diseases of the mind, whose danger consists in their frequency and duration.  Wisdom is only the sum of these intervals of health which we enjoy between the paroxysms of passion, and this sum is not entirely made up of happiness; for we then perceive that the mind has been diseased; we accuse our passions; we condemn our actions.  Folly is the germ of misery, and wisdom unfolds it.  Most people who call themselves unhappy, are passionate men, or, in other words, fools, who have some intervals of reason, during which they perceive their folly, and, of course, feel their misery:  And as, in the elevated conditions of life, there are more false appetites, more vain pretensions, more disordered passions, more abuse of the mind, than in the inferior, men of birth and opulence must unquestionably be the most unhappy.  [243]

            But, let us turn from these melancholy objects, these humiliating truths, and consider the wise man, who alone merits examination.  He is both master of himself and of events.  Content with his condition, he desires not to live in any other manner than he has always lived:  Possessed of sufficient resources, he seldom requires the aid of others.  Occupied perpetually in exercising the faculties of his mind, he improves his understanding, cultivates his genius, acquires fresh sources of knowledge; and, being neither tormented with disgust nor remorse, he enjoys the universe, by enjoying himself.

            Such a man is, doubtless, the happiest being in nature.  To the pleasures of the body, which he possesses in common with the other animals, he joins those of the mind, that are peculiar to him.  He has two modes of being happy, which mutually aid and fortify each other; and if, by disease or accident, he be afflicted with pain, he suffers less than the fool:  He is supported by the strength of his mind, and reason affords him consolation:  Even in suffering pain, he has the pleasure of perceiving that he is able to endure it.

            Health, in man, is more feeble and precarious than in any other animal.  He is oftener sick; his sickness is of longer duration; and he dies at every age.  The brutes, on the contrary, seem to run through the space allotted to their existence with firm and equal steps.  This circum- [244] stance appears to proceed from two causes, which, though very different, mutually contribute to produce the same effect.  The first is the agitation of mind occasioned by the derangement of our internal material sense.  The passions have an influence on health, and introduce disorder into the vital principles.  The majority of men lead either a timid or contentious life, and most of them die of chagrin.  The second is the imperfection of those of our sense which are analogous to appetite. The brute animals distinguish better what is agreeable to their nature:  They are never deceived in the choice of their aliment; they never exceed in their pleasures; guided only by the perception of their actual wants, they remain satisfied, and never search for new sources of gratification.  But man, independent of wishing for excess in every article, independent of that ardour with which he seeks to destroy himself by attempting to force nature, is not so alert in distinguishing the effects of particular species of food.  He despises simple aliment, and prefers compounded dishes, because his taste is corrupted, and because he has converted the sense of pleasure into an instrument of debauchery, which can only be gratified by irritation.

            It is not, therefore, surprising that we are more subject to diseases than the brutes, since we cannot, like them, distinguish so easily what is noxious or salutary to our frame.  Our experi- [245] ence, in this article, is less certain than their sentiment.  Besides, we even abuse those sensations of appetite, which they possess in a more perfect degree:  In brutes, these sensations are the means of health and preservation; but, in man, they become the causes of malady and destruction.  Intemperance alone is more fatal to man than the united force of all the other evils incident to human nature.

            By these considerations we are led to believe, that the feelings of animals are more determined and more exquisite than ours; for, though it were allowed that brutes frequently poison themselves, it must likewise be granted, that they never taken poison but when concealed among other food, or when so pressed with hunger, that they eat whatever is presented to them; and many instances have occurred where animals have perished for want, rather than eat what was repugnant to their constitution.

            The superior strength of sentiment in brutes may be still farther proved, by attending to their sense of smelling, which, in most animals, is so powerful, that they smell farther than they see:  They not only scent actual objects at a distance, but they can trace them by their effluvia long after they are gone.  Such a sense is an universal organ of perception; it is an eye that sees objects, not only where they are, but where they have been.  In a word, it is a sense by which the animal is enabled to distinguish with certain- [246] ty what is agreeable to its nature, and by which it perceives what is fitted to gratify its appetite.  Hence brute animals enjoy, in a superior degree, the senses relative to appetite; and, of course, have feelings more exquisite than those of men. They are likewise conscious of their actual existence; but retain no consciousness of their past existence. This latter proposition, as well as the first, merits consideration.

[I separated this lengthy article into separate sections.  Click here for the continuation]

* See above, Vol. II. Chap. 1 [back to page 209].