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A DISSERTATION ON THE NATURE of ANIMALS.

ALL our knowledge is derived from com|paring 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 na|ture of the animal world; let us investigate their organization, and study their general oeconomy. This inquiry will enable us to draw particular in|ferences, Page  209 to discover relations, to reconcile appa|rent 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 com|mon to animated as well as inanimated beings, belong not to our subject*. The qualities pos|sessed by plants as well as animals, ought like|wise to be rejected. It is for this reason that we have treated of nutrition, of growth, of re|production, and even of generation, properties common to the plant and animal, before enter|ing upon those qualities which are peculiar to, and constitute animated bodies.

In the next place, as many beings are com|prehended in the class of animals, whose orga|nization 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 be|ings.

Page  210 Having thus circumscribed our subject, and lopt 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 ma|chine; 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, all is at rest, excepting one part, and that part acts e|qually 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 inde|pendent 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 inter|ruption; the other is less essential, because it acts only by 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 a|sleep, as when awake and in action. This di|stinction 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 Page  211 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 na|turally, 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 for|mer; and the action of the senses, joined to the movements of the members, constitute the lat|ter.

If we conceive the existence of beings endow|ed 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 orga|nized being, deprived of sense and motion, may Page  212 be compared to an animal constrained by Nature to perpetual sleep.

Sleep, in the animal, therefore, is not an ac|cidental state induced by the exercise of its func|tions while awake: It is, on the contrary, an essential mode of existence, and serves as a basis to the animal oeconomy. Our being commen|ces 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 con|trary, 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 com|mences: All organized beings, which are not en|dowed 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 Ani|mal. 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, Page  213 grow, expand, and are endowed with internal movements and a vegetating life. On this sup|position, they would be equally deprived of progressive motion, action, and sentiment; and they would have no external or apparent cha|racter of animation. But, if this internal part be clothed with a proper cover, or, in other words, if it be endowed with senses and mem|bers, 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 diffe|rent animals. The internal part, which is the basis of the animal oeconomy, is common to e|very animated being, without exception; and, as to its mōde, 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, name|ly the heart and lungs, or the organs of circula|tion 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 Page  214 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 num|ber 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, if we attend to the following cir|cumstances. 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 ter|minated by a tail, which consists of a certain number of external vertebrae, which exist not in man. In the same manner, the inferior extre|mity of the head, or jaw-bones, and the superior, Page  215 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 consi|derable, till we arrive at the extremities, where they are by much the greatest. But, where this centre, or the heart itself, differs, then the ani|mal is infinitely removed from man, and posses|ses 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 func|tions, 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. Insects, accordingly, differ as much as possible from man and the qua|drupeds. A slight variation in the central parts is always accompanied with an amazing differ|ence Page  216 in the external configuration. The heart of a turtle is of a singular structure; and its figure is so extraordinary, that it has no resem|blance to any other creature.

In contemplating men, quadrupeds, birds, fishes, and reptiles, what a prodigious variety occurs in the figure and proportion of their bo|dies, in the number and position of their mem|bers, in the substance of their flesh, bones, and integuments? The quadrupeds have tails and horns; and all their extremities differ remark|ably 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 inferior extremities. The birds dif|fer still more from man, by their beak, their fea|thers, their flying, and their multiplication by means of eggs. The fishes and amphibious ani|mals are still farther removed from the human figure; and the reptiles are entirely destitute of members. Thus we find, that the greatest di|versity 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 ani|mal oeconomy, because they are the most con|stant, and least subjected to variation.

Page  217 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 senses, 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 ori|gin of all sensation. Even the infects, 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 re|garded as beings only half animated, and as forming the shade between animal and vege|table life.

Thus we have discovered the brain and the senses to be a second essential part of the animal oeco|nomy. 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 inte|rior parts communicate with the brain and ex|ternal Page  218 cover, by means of the distribution of blood-vessels, the brain has a similar communi|cation with the internal parts by the ramifica|tions of the nerves. This union is intimate and reciprocal; and, though the functions of the two organs be totally different, they cannot be sepa|rated, without instant destruction to the animal.

The heart, and the whole internal parts, act continually, without the smallest interruption, and independent of external causes. But the senses and envelope act only by alternate inter|vals, and successive vibrations excited by exter|nal 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 Sensa|tion: The brain, in consequence of this impres|sion, 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 re|action are always equal. But, in the animal Page  219 body, re-action, or external motion, seems to be incomparably greater than action; and, conse|quently, progressive motion, and the other ex|ternal 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 causes; 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 senses should produce a violent re-action in the animal body, manifesting itself by external movements.

Causes which admit of measurement, and the quantity of whose effects can be exactly estima|ted, 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 Page  220 law; and, of course, they can neither be mea|sured, nor estimated, but by endeavouring to ap|proach 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 ob|jects 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 depri|ved 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 in|voluntarily; 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 inclina|tion 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 Page  221 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 no|thing to desire. Desire, then, originates from our being ill situated with regard to the object perceived. We are either too near or too di|stant from it. We, therefore, naturally change our situation; because, at the same time that we perceive the object, we also perceive the obstruc|tion 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 ob|ject; and they would never fail to succeed the impression, if this natural effect were not opposed by other impressions, which, by acting at the Page  222 same time, often weaken and efface the action of the first.

An organized being, therefore, without sen|sation, 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 equal|ly excite desire, and this desire would manifest itself by external movements. I am uncertain whether beings deprived of senses have any per|ception 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 ap|proach 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 depri|ved of every faculty of motion, he would still exert all his force to obtain a change of situa|tion: 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.

Page  223 The facility, the quickness, the direction, and the continuation of motion, depend, it is true, upon external organization: But the cause, prin|ciple, and determination of it, proceed solely from desire, excited by the impression of objects upon the senses; 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 de|prived of any of the other senses; and, if depri|ved 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 pro|duce external motion in animals; and, provided they are not entirely deprived of external senses, 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 with|out 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 Page  224 does the action of objects excite desire or aver|sion? 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 ani|mal action, and even sometimes counteract it, notwithstanding the impression of objects.

With regard to man, whose nature is so dif|ferent from that of other animals, this question is difficult to solve; because the soul participates all our movements; and it is not easy to distin|guish 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 de|pend absolutely on their organization.

I apprehend, therefore, that, in the animal, the action of objects on the senses produces an|other on the brain, which I consider as a ge|neral internal sense, that receives all the impres|sions Page  225 transmitted to it by the external senses. This internal sense is not only susceptible of vi|brations from the action of the senses, but is ca|pable 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 facul|ty which it possesses of receiving every species of impression; while the external senses are only affected in one mode, corresponding to their con|formation: 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 ex|ternal senses, are pure results of matter and me|chanical 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 impres|sions or vibrations continue longer in the internal Page  226 than the external senses. Of this we may easily form a conception, since the duration of impres|sions, even on the external senses, is very diffe|rent. 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 in|ternal sense by the eye are stronger than those conveyed by the ear, and that we describe ob|jects which we have seen in a more lively man|ner than 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 ex|panded 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 en|tirely of nervous fibres, and is only a prolon|gation of the organ in which the internal sense resides. It is not, of course, surprising that it should make the nearest approach to this inter|nal sense. Its impressions are not only more durable, but, like the internal sense, it possesses Page  227 powers of a nature superior to those of the other senses.

The eye exhibits external marks of internal impressions. It expresses desire or aversion ex|cited by agreeable or disagreeable objects. Like the internal sense, it is active; but all the other senses are purely passive: They are simple or|gans, destined for the reception of external im|pressions, but incapable of preserving or reflect|ing 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 ob|ject has ceased. But the eye possesses this power in a supereminent degree; and it is only exceed|ed by the brain, which not only preserves the impressions received, but propagates their ac|tion by communicating vibrations to the nerves. The external organs of sense, the brain, the spinal marrow, and the nerves, which are ex|panded over the whole body, ought to be re|garded 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 diffe|rent from all others is, that its fulcrum not only resists and re-acts, but is even active itself; be|cause it long retains received impressions. And, as this internal sense, the brain and its mem|branes, Page  228 is very large, and endowed with great sensibility, it can admit many successive and con|temporary vibrations, and retain them in the same order they were received; because each im|pression communicates vibrations to one part only of the brain, and successive impressions af|fect the same part, or contiguous parts, in a dif|ferent manner.

If we suppose an animal deprived of a brain, but endowed with an external sense of great ex|tent and sensibility, as an eye, for example, ha|ving 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 me|chanically 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 deter|mined to move, in order to gratify this appetite: But, if the number and force of different images were equal, the animal, having no superior mo|tive, would remain at rest. I say, that all this Page  229 would happen mechanically, and without the intervention of memory; for, by seeing and be|ing acted upon by all the images at the same time, those which correspond with desire would be opposed by those that correspond with aver|sion, and from this equilibrium, or from the ex|cess in number or force of one set of images a|bove another, the animal could alone be deter|mined 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 re|ceived impressions. This faculty is alone suffi|cient 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 senses of exquisite acute|ness; but, in general, they are not all equal to those of man: And, it is worthy of remark, that the degrees of excellence in the senses fol|low 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 the other animals. The sense of smelling is most analogous to instinct and appetite; and the brute enjoys it in a supe|rior degree. Hence man should excell in know|ledge, and the brute in appetite. In man, the Page  230 first sense for excellence is touching, and smel|ling is the last: In the brute, the sense of smel|ling 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 ex|ceeding imperfect and delusive, without the aid of that of touching; and the former, according|ly, 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 senses, the animals also possess it in a superior degree, as ap|pears from their invincible aversion against cer|tain 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 mancinella like an apple, and the hemlock like parsley.

The excellence of the senses is the gift of na|ture; but art and habit may bestow on them a greater degree of perfection. A musician, whose ear is accustomed to harmony, is shocked with Page  231 discord: A painter, with one glance of his eye, perceives a number of shades which escape a com|mon observer. The senses and even the appetites of animals may also be improved. Some birds learn to sing, and to repeat words; and the ar|dor of a dog for the chace 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 insen|sible 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 dif|ferent, 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, a|nalogous to the external senses. Inspection a|lone 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 Page  232 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 o|perations. In the animal, this sense is the prin|ciple 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 furnish|ed with a criterion for distinguishing what we possess in common with the other animals, and in what articles we excell them.

The internal material sense receives indiffe|rently every impression conveyed by the exter|nal senses. These impressions proceed from the action of objects, and quickly pass through the external senses, where they only excite momen|tary vibrations. But their progress stops at the brain, and produce, in this organ of the internal sense, vibrations which are both distinct and du|rable. These vibrations give rise to desire or aver|sion, 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 ef|fluvia of the milk contained in the dugs of the Page  233 mother. Vibrations are excited in this sense by the odorous particles, and these vibrations are transmitted to the brain, which, in its turn, acts upon the nerves; and the animal is thus stimu|lated to make the proper movements, or, in o|ther words, to open its mouth, in order to pro|cure the nourishment desired. The senses pe|culiar to appetite being more obtuse in man than in the brutes, the new-born child feels only the desire of taking nourishment, which he announ|ces by crying. But he is incapable of procu|ring it himself; neither is he stimulated by the sense of smelling; his mouth must be applied to the breast, before he can use the means of gra|tifying his appetite. Then, indeed, the senses of smelling and of touching communicate vibra|tions to the brain, which, by re-acting on the nerves, stimulates the child to make the neces|sary 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 place 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 ap|petite, is open in man from the moment of birth; but remains shut, in most other animals, for se|veral days. The senses of appetite, on the con|trary, are more perfect and mature in the young Page  234 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 exter|nal movements. It is long before the infant can use its members, or has strength enough to change place. But a young animal soon ac|quires these faculties. These powers, in the a|nimal, are all relative to appetite, which is ve|hement, quickly unfolded, and the sole princi|ple of motion. But appetite, in man, is feeble, long before it is unfolded, and ought not to have such influence, as intelligence, upon the deter|mination 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 ac|tuated by appetite only, and that man is influ|enced 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 intelli|gence; 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.

Page  235 The internal material sense, as formerly re|marked, retains, for a long time, the vibrations it receives. This sense, the organ of which is the brain, is common to every animal, and re|ceives 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 com|municate motion to the animal. When the impression proceeds from the senses of appetite, the movement is determined, the animal either advances to lay hold of the object, or flies to a|void it. This motion may be uncertain, when the impression is transmitted by the senses ana|logous 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 analo|gous 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, Page  236 makes a number of movements in order to ob|tain 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 belongs to another, but is restrained by the fear of punishment? This is the vulgar mode of accounting for the conduct of animals. We naturally transfer our own motives to ani|mals, 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 simi|lar. Though this analogy, however, were just, is not something more required? Is it not neces|sary that the animals should, on some occasions, do every thing which we perform? But the con|trary 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, with|out the necessity of ascribing to them the powers of reflection.

Their internal sense is strongly agitated by e|very thing that relates to their appetites. A Page  237 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 accom|pany those of appetite, because they have always been made at the same time. The animal being thus acted upon at once by two contrary impul|ses, which mutually destroy each other, he re|mains in equilibrio, between two equal powers. The cause determining him to motion being coun|terbalanced, he makes no effort to obtain the object of his desire. But, though the vibrations occasioned by appetite and aversion, or by plea|sure 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 prin|ciples, may all the actions of animals, however complicated they appear, be explained, without Page  238 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 ask|ed, no knowledge, no sentiment, or no conscious|ness 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 read|er 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 compa|rison of sensations.

Let us consider each of these articles separate|ly. The feelings of animals are more exquisite than those of man. This, I imagine, has al|ready been sufficiently proved by what was re|marked concerning the excellence of their senses relative to appetite; by their natural and invin|cible aversion against certain objects, and their Page  239 uniform and determined attachment to others; and by their faculty of instantly distinguishing with certainty what is salutary or noxious. A|nimals, 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 conformable or repugnant to their na|ture and organization. The pleasure of tickling, and the pain of an wound, are common to us and the animals; because they depend absolutely upon an external material cause, namely, a weak|er 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 plea|sure.

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 mode|rate heat, a soft sound, a delicate perfume, a fine favour, 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 Page  240 causes, therefore, which give rise to violent im|pressions, 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 a|greeable to them, the sum of agreeable sensations must exceed that of the disagreeable; and there|fore 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 phy|sical evil, it is evident, that every sentient being must enjoy more pleasure than pain; for every thing that corresponds with his nature, contri|butes to his preservation, or supports his exist|ence, 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 be|ing can continue to exist; and, if the sum of agreeable sensations surpassed not that of the dis|agreeable, deprived of pleasure, he would first languish for want of good, and, loaded with pain, he would next perish by a superabundance of evil.

Page  241 In man, physical good and evil constitute the smallest part of his pleasures and pains. His i|magination, 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 chime|ras 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 sine, 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 fa|culty of discerning and of judging without pas|sion.

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 enjoy|ment 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 plea|sure 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|cal Page  242 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 plea|sure would be more pure and copious, were its current not interrupted by our passions, which destroy all contemplation. Whenever they ob|tain the ascendant, reason is silenced, or only makes feeble and unavailing efforts. We, of course, lose all relish of truth; the charm of illu|sion 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 pas|sion, to act only according to its dictates, to ap|pear, consequently, unjust or ridiculous to others, and, lastly, to be obliged to despise ourselves, whenever we can command a moment's re|flection?

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 know|ledge, and we would employ her only for those Page  243 of sensation. If we could extinguish her light entirely, instead of regretting the loss, we would envy the condition of idiots. As we only rea|son by intervals, and as these intervals are bur|densome to us, and pass in secret reproaches, we wish to suppress them. Thus, proceeding always from illusion to illusion, we voluntarily seek to lose sight of ourselves, and to terminate the whole by forgetting our existence.

Uninterrupted passion is madness; and mad|ness is the death of the soul. Violent passions, with intervals, are paroxysms of folly, diseases of the mind, whose danger consists in their fre|quency and duration. Wisdom is only the sum of these intervals of health which we enjoy be|tween 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 un|folds it. Most people who call themselves un|happy, 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 con|ditions 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.

Page  244 But, let us turn from these melancholy ob|jects, these humiliating truths, and consider the wise man, who alone merits examination. He is both master of himself and of events. Con|tent with his condition, he desires not to live in any other manner than he has always lived: Possessed of sufficient resources, he seldom re|quires the aid of others. Occupied perpetually in exercising the faculties of his mind, he im|proves 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 en|dure 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 exist|ence with firm and equal steps. This circum|stance Page  245 appears to proceed from two causes, which, though very different, mutually contribute to produce the same effect. The first is the agita|tion 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 im|perfection of those of our senses which are analo|gous to appetite. The brute animals distinguish better what is agreeable to their nature: They are never deceived in the choice of their ali|ment; 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, inde|pendent 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 par|ticular species of food. He despises simple ali|ment, and prefers compounded dishes, because his taste is corrupted, and because he has con|verted 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|ence, Page  246 in this article, is less certain than their sen|timent. 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 be|come the causes of malady and destruction. In|temperance alone is more fatal to man than the united force of all the other evils incident to hu|man 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 them|selves, it must likewise be granted, that they ne|ver take 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 re|pugnant 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 univer|sal 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|ty Page  247 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 ex|istence; but retain no consciousness of their past existence. This latter proposition, as well as the first, merits consideration.

In man, consciousness of existence is composed of the perception of actual existence, as well as remembrance of past existence. Remembrance is a perception equally present with the first im|pression; it even sometimes affects us more strongly than actual sensations. As these two species of sensation are different, and as the mind has the faculty of comparing and forming ideas from them, the consciousness of our existence is more certain and extensive, in proportion to the number and frequency of past objects recalled by the memory, and to the frequent combining and comparing of them with each other, and with present objects. Each object is accompanied with a certain number of sensations, or different existences, relative to the different states in which it was originally perceived. This number of sensations, by the comparison made between them by the mind, becomes a succession or train of ideas. The idea of time, and indeed every other idea, originates from the comparison of our sensations. But this train of ideas, or of Page  248 existences, often presents itself to us in an order or arrangement very different from that in which our sensations were received. It is the arrange|ment of our ideas that we perceive, and not the order of our sensations; and in this consist chiefly the differences of character and of ge|nius; for two men, though similar in organiza|tion, and educated in the same manner, and though they received their sensations in the same order, might, notwithstanding, think very dif|ferently. As the temperament of their minds was not the same, and as each combined and compared similar sensations in a manner peculiar to himself, the general results of these compari|sons, or the ideas, genius, and character acqui|red, would likewise be different.

Some minds are peculiarly active in compa|ring sensations and forming ideas. Such men are always the most ingenious, and, if not pre|vented by circumstances, make the most brilliant figure in life. There are others, whose minds being more obtuse, allow every sensation to e|scape, but such as make strong impressions: These men have less genius and vivacity than the former. Lastly, there are other men, and these constitute the multitude, who have so little activity of mind, and so great an aversion from thinking, that they never compare or combine sensations, at least, quickly. The sensations must be strong, and repeated a thousand times, before their minds can be roused to compare Page  249 them, or to form ideas. These men are exceed|ingly stupid, and only differ from the brutes by the small number of ideas which their minds have formed with so much labour.

The consciousness of our existence being thus composed not only of our actual sensations, but of the train of ideas which results from a com|parison of our sensations, and of our past exist|ences, it is evident, that the more ideas a man possesses, he is more certain of his existence; that his existence is proportioned to his genius; and that, by the power alone of reflection, we are conscious of our former existence, and that we will continue to exist, the idea of future be|ing only the inverse comparison of the present with the past; for, in this view, the present is past, and the future present.

Now, the power of reflection being denied to brutes, it is obvious, that they cannot form ideas, and, consequently, that their consciousness of their existence must be less certain and less extensive than ours; for they have no idea of time, no knowledge of the past, or of the future. Their consciousness of existence is simple; it depends solely on the sensations which actually affect them, and consists of the internal feelings produced by these sensations.

We may, perhaps, acquire some notion of the consciousness of existence which animals possess, by reflecting on our own condition, when Page  250 strongly occupied with any object, or so vio|lently agitated with passion as to preclude every reflex idea of ourselves. This condition is ex|pressed by saying, A man is absent, or out of himself. We are out of ourselves when fully immersed in actual sensations, and especially when these sensations are violent, rapid, and leave the mind no leisure to reflect. In this state, we feel every degree of pleasure and pain; we even retain the consciousness of our existence, without any sensible participation of the mind. This condition, in which we have only momen|tary impressions of our existence, is the habitu|al state of animals; deprived of ideas, and fur|nished with sensations, they know not their ex|istence, but they feel it.

To illustrate this difference more fully, let us compare the powers and actions of brute ani|mals with those of man. Like us, they have senses, and receive impressions from exernal objects. They have also an internal sense, an organ which retains the vibrations excited by these impressions; and, consequently, sensations, which, like ours, may be renewed, and are more or less strong and durable. Still, however, they have neither imagination, understanding, nor memory; because they possess not the power of comparing their sensations, and because these three faculties of the mind depend upon this power.

Page  251 Have brute animals no memory? The con|trary, I shall be told, is demonstrably evident: Do they not recollect, after long absence, the persons with whom they have lived, the places where they dwelt, the roads they frequented? Do they not remember the chastisements they had suffered, the caresses they had received, the lessons they had been taught? Every thing con|curs in showing that, though deprived of imagi|nation and reason, they possess an active, exten|sive, and, perhaps, more faithful memory than our own. But, however striking these appear|ances may be, and however strong the prejudices to which they have given rise. I imagine it is capable of demonstration that they are deceitful, and that the brutes have no knowledge of past events, no idea of time, and, of course, no me|mory.

In man, memory originates from the faculty of reflection; for our remembrance of past e|vents supposes not only a continuation of the impressions made upon the internal material sense, or a renewal of former sensations, but likewise the comparison the mind makes between its sensations, or the ideas it forms. If memory consisted not in the renovation of past sensations, these sensations would be represented in our in|ternal sense, without leaving any determined impressions; they would be exhibited without order or connection, like the ravings of persons mad or intoxicated, where objects are so de|ranged Page  252 and confused, that no remembrance of them is retained; for we cannot remember things that have no relation to those which have preceded or followed them. No isolated sensa|tion, however strong, can leave any traces on the mind. Now, it is the mind alone that ascer|tains the relations of objects, by the comparison it makes between them, and connects our sen|sations by a continued train of ideas. Memory, therefore, consists in a succession of ideas, and necessarily supposes the existence of the power by which they are produced.

But, to leave no room for doubt on this im|portant point, let us examine that species of re|membrance left by our sensations, when unac|companied with ideas. Pain and pleasure are sensations of the purest and strongest kind; yet our recollection of these feelings is feeble and confused. We only remember that we felt pleasure or pain; but our remembrance is indi|stinct: We cannot figure either the species, the degree, or the duration of those feelings which af|fected us so powerfully; and still less are we able to have clear ideas of those which have been seldom repeated. A violent pain, for example, which is felt but once, continues only a few moments, and differs from all former pains, would neces|sarily be soon forgot. We might recollect that we felt a great pain; but, while we distinctly remembered the circumstances which attended it, Page  253 and the time when it happened, we would have only a faint impression of the sensation itself.

Why is every thing that passed in our infancy entirely obliterated? Why do old men recollect what happened in their youthful years better than what occurred during their old age? Can there be a stronger proof that sensations alone are insufficient for the production of memory, and that it has no existence but in the train of ideas which the mind forms from its sensations? In infancy, our sensations are perhaps as lively and rapid as in middle age; yet they leave little or no traces behind them; because, at this period, the power of reflection, which alone forms ideas, is almost totally inactive; and, when it does act, its comparisons are superficial, and it is incapable of reducing objects to any regular arrangement. At the age of maturity, reason is fully unfold|ed, because the power of reflection is at its me|ridian. We then derive from our sensations all the fruit they can produce, and we form various orders of ideas and chains of thought, each of which, by being frequently revolved, makes an impression so deep and indelible, that, when old age arrives, the same ideas recur with more force than those derived from present sensations; be|cause, at that period, our sensations are slow and feeble, and the mind itself participates the lan|guor of the body. Infancy is totally occupied with the present time: In mature years, we en|joy equally the past, the present, and the future; Page  254 and, in old age, we have but slight feelings of the present, we turn our eyes to futurity, and only live in the past. Do not these differences depend entirely on the arrangement the mind has made of its sensations; and are they not more or less connected with the faculty we possess, at different ages, of forming, acquiring, and retain|ing ideas? Neither the prattling of the child, nor the garrulity of old age, have the tone of reasoning, because they are equally deficient in ideas; the first is yet unable to form them, and the last has lost the faculty.

An idiot, whose senses and bodily organs ap|pear to be perfectly sound, possesses, in common with us, every kind of sensation, and, if he li|ved in society, and were obliged to act like other men, he would possess them in the very same or|der. But, as these sensations give rise to no i|deas; as there is no correspondence between his mind and his body; and, as he has not the facul|ty of reflection; he is, of course, deprived of me|mory, and of all knowledge of himself. With regard to external powers, this man differs not from the brutes; for, though he has a soul, and possesses the principle of reason, as this principle remains inactive, and receives no intelligence from the bodily organs, it can have no influence on his actions, which, like those of the brute animals, are solely determined by his sensations, and by the consciousness of his actual existence and present wants. Thus, an idiot and a brute Page  255 are beings whose operations are in every respect the same; because the latter has no soul, and the former makes no use of it: Both want the power of reflection, and, consequently, have neither understanding, imagination, nor memo|ry; but they both possess sensations, feelings, and the faculty of moving.

If it shall still, however, be asked, Do not idiots and brutes often act as if they were deter|mined by the knowledge of past objects? Do they not recollect the person with whom they have lived, the places where they dwelt, &c.? Do not these actions necessarily imply the exer|tions of memory? and, does not this prove that memory flows not from the power of reflec|tion?

The reader ought to recollect, that I have al|ready distinguished two species of memory, which, though they resemble each other in their effects, proceed from very different causes: The first is occasioned by the impressions of our ide|as; and the second, which I would rather call reminiscence than memory, is only a renewal of our sensations, or of the vibrations that produced them. The first is an emanation of the mind, and, as already remarked, is more perfect in man than the second. But the latter is only a renovation of the vibrations of the internal ma|terial sense; and it alone is possessed by idiots and brute animals. Their former sensations are re|newed by actual sensations; the principal and Page  256 present recall the accessory and past images; they feel as they formerly felt, and consequently act as they formerly acted; they perceive the present and the past; but they have not the ca|pacity of distinguishing, or comparing objects, and, of course, have no proper knowledge of them.

I am aware that dreams will be adduced as another proof of the memory of brutes. It is undeniable, that the objects which occupy ani|mals when awake, are likewise presented to them during sleep. Dogs bark in their sleep; and, though this barking be feeble, it is easy to distin|guish the sounds peculiar to the chace, to anger, to desire, to complaint, &c. It is, therefore, unque|stionable, that dogs have a lively and active me|mory, and very different from what has been a|bove described, since it acts independent of ex|ternal causes.

To obviate this difficulty, we must examine the nature of dreams, and inquire whether they proceed from the mind, or depend solely on our internal material sense. If we can prove that they reside entirely in the latter, the objection will not only be removed, but a new demon|stration will be furnished against the understand|ing and memory of brutes.

Idiots, whose minds are totally inactive, dream like other men: Dreams, therefore, are produ|ced independent of the mind. Brute animals, though they have no mind, not only dream, but Page  257 I am tempted to think that all dreams are inde|pendent of mind. Let any man reflect upon his dreams, and endeavour to discover why the parts of them are so ill connected, and the events so ridiculous and absurd. The chief reason, I have always thought, proceeds from this circum|stance, that dreams are entirely derived from sen|sations, and not from ideas. The idea of time, for example, never enters into dreams: Persons whom we never saw are represented; we even see those who have been long dead in the same form as when they were alive; but they are al|ways connected with present objects and persons, or with those which are past. It is the same with the idea of place: In dreams we never see per|sons where they are; objects must be seen where they are not, or they cannot be perceived at all. If the mind acted, it would instantly reduce this chaos of sensations to order. But, instead of acting, the mind generally allows these illusory representations to succeed each other in the order they occur; and, though each object appears in lively colours, the succession is often confused, and always chimerical. If, however, the mind be half roused by the absurdity of the represen|tations, or by the mere force of the sensations, a glimmering of light breaks in upon the dark|ness, and produces a real idea in the midst of chimeras; we then begin to dream, or rather to think, that the whole may be only a dream. Though this action be only a feeble exertion of Page  258 the mind, it is neither a sensation nor a dream; it is a real thought or reflection; but, as it has not strength enough to dissipate the allusion, it mixes with, and becomes part of the dream, and allows the succession of images to proceed; so that, when we awake, we imagine we have dreamed what we in reality thought.

In dreams we see much, but seldom under|stand: Though we feel in the most lively man|ner, we never reason: Images and sensations succeed each other; but the mind never unites or compares them. We have, therefore, sensa|tions, but no ideas; for ideas are the results of compared sensations. Hence dreams reside on|ly in the internal material sense; they are pro|duced without the intervention of the mind; and, therefore, constitute a part of that material or purely animal reminiscence which we have formerly mentioned. Memory, on the contra|ry, cannot exist without the idea of time, with|out the actual comparison of former ideas; and, since ideas enter not into dreams, it is obvious, that they can neither be a consequence, nor an effect, nor a proof of memory. But, though i|deas should sometimes accompany dreams, though the somnambulists, who walk, speak sensibly, answer questions, &c. in their sleep, should be quoted to prove that ideas are not so entirely ex|cluded from dreams as I pretend, it is sufficient for my purpose that dreams may be produced by the renewal of sensations alone, without the intervention of mind: For then brute animals Page  259 can only have dreams of this species; and these dreams, instead of supposing the existence of memory, indicate, on the contrary, nothing more than a material reminiscence.

I am, however, far from believing that som|nambulists are really occupied with ideas: The mind seems to take no part in their actions; for, though they go about and return, they act without reflection or knowledge of their situ|ation. They are neither conscious of the dan|gers nor inconveniencies which accompany their expeditions. The animal faculties are alone em|ployed, and even not the whole of them. A somnambulist, therefore, is in a more stupid state than that of an idiot; because he exerts only a part of his senses; but an idiot employs the whole, and enjoys extensively every species of feeling: And as to the people who speak during sleep, they never say any thing new. The an|swering some trivial questions, the repetition of some common phrases, prove not the action of the mind: All this may be performed indepen|dent of the thinking principle. Why may not a man asleep speak without thinking, since per|sons fully awake, especially when occupied with passion, utter many things without reflection?

With regard to the occasional cause of dreams, or the reason why former sensations are renew|ed, without being excited by present objects, it may be remarked, that we never dream during a profound sleep. Every thing is then extin|guished; Page  260 we sleep both externally and internally. But the internal sense sleeps last, and awakes first; because it is more active, and more su|sceptible of impressions than the external senses. We dream most, when our sleep is least perfect and profound. Former sensations, especially those which require no reflection, are renewed. The internal sense, occupied with actual sensa|tions, on account of the inactivity of the exter|nal senses, exercises itself with its past sensations. The strongest always present themselves first; and the stronger they are, the supposed situations become more keenly interesting. It is for this reason that dreams are almost perpetually either dreadful or ravishing.

It is not even necessary that the external senses should be absolutely lulled, before the internal sense can exert its independent powers: The simple inaction of these senses is sufficient to pro|duce this effect. The habit of going to repose at stated times often prevents us from sleeping easily. The body and its members are softly extended without motion; the eyes are involved in darkness; the tranquility of the place, and the silence of the night, render the ear useless; the other senses are equally inactive; all is in a state of repose, but nothing as yet entirely lulled or asleep. In this condition, and when the mind is also unoccupied with ideas, the internal material sense alone exerts itself. This is the season of illusive images and fleeting shades. We are a|wake, Page  261 and yet we feel the effects of sleep. If we be in health and vigour, the succession of i|mages and illusions is enchanting. But, when the body is disordered, or fatigued, the images are of a different nature: We are then torment|ed with hideous and threatening phantoms, which succeed each other with equal whimsicalness and rapidity. This scene of chimeras may be cal|led a magic lanthorn which fills the brain with illusions, when void of all other sensations: The objects of this scene are more lively, numerous, and disagreeable, in proportion to the weakness of the body and delicacy of the nerves; for, the vibrations occasioned by real sensations being, in a state of weakness or disease, much stronger and more disagreeable than in a healthy state, the re|presentations of these sensations, produced by a renewal of the same vibrations, must likewise be more lively and painful.

In fine, we remember dreams for the same reason that we remember former sensations: The only difference between us and the brutes is, that we can distinguish dreams from ideas or real sen|sations; and this capacity of distinguishing is a result of comparison, an operation of memory, which includes the idea of time. But the brutes, who are deprived of memory and of the faculty of comparing past and present time, cannot di|stinguish their dreams from their actual sensa|tions.

Page  262 In the article concerning the nature of man, I imagine I have proved, in a satisfactory man|ner, that animals possess not the power of reflec|tion. Now, the understanding, which is a re|sult of this power, may be distinguished by two different operations: The first is the faculty of comparing sensations, and forming ideas from them; and the second is the power of comparing the ideas themselves, and forming a chain of reasoning. By the first operation, we acquire particular ideas, or the knowledge of sensible ob|jects: By the second, we form general ideas, which are necessary for the acquisition of abstract truths. The brute animals possess neither of these faculties, because they have no understanding; and the understanding of the bulk of mankind seems to be limited to the first of the above ope|rations.

If all men were equally capable of comparing and generalizing ideas, they would equally exhi|bit their ingenuity by new productions, which would be always different from those of others, and often more perfect; all men would be en|dowed with inventive powers, or, at least, with the capacity of improving and perfecting. But this is by no means the case: Reduced to a ser|vile imitation, most men execute only what they have seen performed by others; they think only from memory, and in the same order as others have thought; their understanding is limited en|tirely Page  263 to form and imitation, and their power of reflecting is too feeble for invention.

Imagination is another faculty of the mind: If, by imagination, we understand the power of comparing images with ideas, of illuminating our thoughts, of aggrandizing our sensations, of painting our sentiments, in a word, of perceiving with rapidity all the qualities and relations of objects, this power is the most brilliant and most active faculty of the mind, and the brutes are still more devoid of it, than either of understand|ing or memory. But there is another species of imagination, which depends solely on corporeal organs, and is common to us with the brutes, namely, that tumultuary emotion excited by ob|jects analogous or opposite to our appetites, that lively and deep impression of the images of ob|jects, which perpetually and involuntarily re|curs, and forces us to act, like the brutes, with|out deliberation or reflection. By this represen|tation of objects, which is more active than their presence, every thing is exaggerated, and paint|ed in false colours. This species of imagination is the grand enemy of the human mind: It is the source of illusion, the mother of those pas|sions which, in spite of the efforts of reason, rule over us, and render us the unhappy theatre of a perpetual combat, in which we are almost con|stantly vanquished.