ANIMAL, in natural history, an organized and living body, which is also endowed with sensation: thus, minerals are said to grow or increase, plants to grow and live, but animals alone to have sensation.
It is this property of sensation alone that can be deemed the essential characteristic of an animal; and by which the animal and vegetable kingdoms seem to be so essentially separated, that we cannot even imagine the least approximation of the one to the other. Those naturalists, indeed, who have supposed the distinction between animals and vegetables to consist in any thing else than what we have already mentioned, have found themselves greatly embarrassed; and have generally agreed, that it was extremely difficult, if not impossible, to settle the boundaries between the animal and vegetable kingdoms. But this difficulty will be easily seen to arise from their taking the characteristic marks of the animal kingdom, from something that was evidently common to both. Thus, Boerhaave attempted to distinguish an animal from a vegetable, by the former having a mouth, which the latter has not: but here, as the mouth of an animal is only the instrument by which nourishment is conveyed to its body, it is evident, that this can be no essential distinction, because vegetables also require nourishment, and have instruments proper for conveying it into their bodies; and where the end is the same, a difference in the means can never be essential. The fixing the difference in an animal's having a gullet, stomach, and intestines, as is done by Dr Tyson, is as little to the purpose.
The power of moving from one place to another, hath by many been thought to constitute their difference; and indeed, in most cases, it is the obvious mark by which we distinguish an animal from a vegetable: but Lord Kaimes hath given several very curious instances of the locomotive power of plants; some of which, as he says, would do honour to an animal.—“Upon the slightest touch, the sensitive plant shrinks back and folds up its leaves, similar to a snail; which on the slightest touch retires within its shell. A new species of the sensitive plant hath been lately discovered*. If a fly perch upon one of its flower-leaves, it closes instantly, and crushes the insect to death. There is not an article in botany more admirable than a contrivance, visible in many plants, to take advantage of good weather, and to protect themselves against bad. They open and close their flowers and leaves in different circumstances: some close before sunset, some after: some open to receive rain, some close to avoid it. The petals of many flowers expand in the sun; but contract at night, or on the approach of rain. After the seeds are fecundated, the petals no longer contract. All the trefoils may serve as a barometer to the husbandman; they always contract their leaves on an impending storm. Some plants follow the sun, others turn from it. Many plants, on the sun's recess, vary the position of their leaves, which is styled the sleep of plants. A singular plant † was lately discovered in Bengal. Its leaves are in continual motion all day long; but when night approaches, they fall down from an erect posture to rest.
“A plant has a power of directing its roots for procuring food. The red whortle-berry, a low evergreen plant, grows naturally on the tops of our highest hills, among stones and gravel. This shrub was planted in an edging to a rich border, under a fruit wall. In two or three years, it over-ran the adjoining deep-laid gravel walk; and seemed to fly from the border, in which not a single runner appeared. An effort to come at food in a bad situation, is extremely remarkable in the following instance. Among the ruins of Newabbey, formerly a monastery in Galloway, there grows on the top of a wall a plane-tree about 20 feet high. Straitened for nourishment in that barren situation, it several years ago directed roots down the side of the wall, till they reached the ground ten feet below; and now the nourishment it afforded to those roots during the time of their descending is amply repaid, having every year since that time made vigorous shoots. From the top of the
Animal. the wall to the surface of the earth, these roots have not thrown out a single fibre; but are now united in a single root.
“Plants, when forced from their natural position, are endowed with a power to restore themselves. A hop-plant, twisting round a stick, directs its course from south to west, as the sun does. Untwist it, and tie it in the opposite direction: it dies. Leave it loose in the wrong direction: it recovers its natural direction in a single night. Twist a branch of a tree so as to invert its leaves, and fix it in that position: if left in any degree loose, it untwists itself gradually, till the leaves be restored to their natural position. What better can an animal do for its welfare? A root of a tree meeting with a ditch in its progress, is laid open to the air. What follows? It alters its course like a rational being, dips into the ground, surrounds the ditch, rises on the opposite side to its wonted distance from the surface, and then proceeds in its original direction. Lay a wet sponge near a root laid open to the air; the root will direct its course to the sponge. Change the place of the sponge; the root varies its direction. Thrust a pole into the ground at a moderate distance from a scandent plant: the plant directs its course to the pole, lays hold of it, and rises on it to its natural height. A honeysuckle proceeds in its course, till it be too long for supporting its weight; and then strengthens itself by shooting into a spiral. If it meet with another plant of the same kind, they coalesce for mutual support; the one screwing to the right, the other to the left. If a honeysuckle twig meets with a dead branch, it screws from the right to the left. The clasps of briony shoot into a spiral, and lay hold of whatever comes in their way for support. If, after completing a spiral of three rounds, they meet with nothing, they try again by altering their course.”
By comparing these and other instances of seeming voluntary motion in plants, with that share of life where-with some of the inferior kinds of animals are endowed, we can scarce hesitate at ascribing the superiority to the former; that is, putting sensation out of the question. Muscles, for instance, are fixed to one place as much as plants are; nor have they any power of motion, besides that of opening and shutting their shells: and in this respect they have no superiority over the motion of the sensitive plant; nor doth their action discover more sagacity, or even so much as the roots of the plane-tree mentioned by Lord Kaimes.
Mr Buffon, who seems to be desirous of confounding the animal and vegetable kingdoms, denies sensation to be any essential distinction. “Sensation (says he) more essentially distinguishes animals from vegetables: but sensation is a complex idea, and requires some explication. For if sensation implied no more than motion consequent upon a stroke or an impulse, the sensitive plant enjoys this power. But if, by sensation, we mean the faculty of perceiving and comparing ideas, it is uncertain whether brute animals are endowed with it. If it should be allowed to dogs, elephants, &c. whose actions seem to proceed from motives similar to those by which men are actuated, it must be denied to many species of animals, particularly to those which appear not to possess the faculty of progressive motion. If the sensation of an oyster, for example, differed only in degree from that of a dog; why do we not ascribe the same sensation to vegetables, though in a degree still
inferior? This distinction, therefore, between the animal and vegetable, is neither sufficiently general nor determined.
“From this investigation we are led to conclude, that there is no absolute and essential distinction between the animal and vegetable kingdoms; but that nature proceeds, by imperceptible degrees, from the most perfect to the most imperfect animal, and from that to the vegetables; and the fresh water polypus may be regarded as the last of animals, and the first of plants.”
It were to be wished, that philosophers would on some occasions consider, that a subject may be dark as well on account of their inability to see, as when it really affords no light. Our author boldly concludes, that there is no essential difference between a plant and an animal, because we ascribe sensation to an oyster, and none to the sensitive plant; but we ought to remember, that, though we cannot perceive a distinction, it may nevertheless exist. Before Mr Buffon, therefore, had concluded in this manner, he ought to have proved that some vegetables were endowed with sensation.
It is no doubt, however, as much incumbent on those who take the contrary side of the question, to prove that vegetables are not endowed with sensation, as it was incumbent on Mr Buffon to have proved that they are. But a little attention will shew us, that the difficulty here proceeds entirely from our inability to see the principle of sensation. We perceive this principle in ourselves, but no man can perceive it in another. Why then does every individual of mankind conclude that his neighbour has the same sensations with himself? It can only be from analogy: Every man perceives his neighbour formed in a manner similar to himself; he acts in a similar manner on similar occasions; &c. Just so it is with brute animals. It is no more doubtful that they have sensations, than that we have them ourselves. If a man is wounded with a knife, for instance, he expresses a sense of pain, and endeavours to avoid a repetition of the injury. Wound a dog in the same manner, he will also express a sense of pain; and, if you offer to strike him again, will endeavour to escape, before he feels the stroke. To conclude, here, that the action of the dog proceeded from a principle different from that of the man, would be absurd and unphilosophical to the last degree.
We must further take notice, that there are sensations essentially distinct from one another; and in proportion as an animal is endowed with more or fewer of these different species, it is more or less perfect as an animal: but, as long as one of them remains, it makes not the least approach to the vegetable kingdom; and, when they are all taken away, is so far from becoming a vegetable, that it is only a mass of dead matter. The senses of a perfect animal, for instance, are five in number. Take away one of them, suppose sight; he becomes then a less perfect animal, but is as unlike a vegetable as before. Suppose him next deprived of hearing: his resemblance to a vegetable would be as little as before; because a vegetable can neither feel, taste, nor smell, and we suppose him still to enjoy these three senses. Let us, lastly, suppose him endowed only with the sense of feeling, which, however, seems to include that of taste; and he is no more a vegetable than formerly, but only an imperfect animal. If this sense is then taken away, we connect him not with the vegetable kingdom, but with what Mr Buffon calls
Animal. brute-matter. It is to this kingdom, and not to the vegetable, that animals plainly approximate as they descend. Indeed, to suppose an approximation between the vegetable and animal kingdoms, is very absurd: for, at that rate, the most imperfect animal ought to be the most perfect plant; but we observe no such thing. All animals, from the highest to the lowest, are possessed of vegetable life; and that, as far as we can perceive, in an equal degree, whether the animal-life is perfect or imperfect: nor doth there seem to be the smallest connexion between the highest degree of vegetation and the lowest degree of sensation. Though all animals, therefore, are possessed of vegetable life, these two seem to be as perfectly distinct and incommensurate to one another, as any two things we can possibly imagine.
The power of vegetation, for instance, is as perfect in an onion or leek, as in a dog, an elephant, or a man: and yet, though you threaten a leek or an onion ever so much, it pays no regard to your words, as a dog would do; nor, though you wound it, does it avoid a second stroke. It is this principle of self-preservation in all animals, which, being the most powerful one in their nature, is generally taken, and with very good reason, as the true characteristic of animal-life. This principle is undoubtedly a consequence of sensation; and as it is never observed to take place in vegetables, we have a right to say that the foundation of it, namely sensation, belongs not to them.—There is no animal, which makes any motion in consequence of external impulse, where danger is threatened, but what puts itself in a posture of defence; but no vegetable whatever does so. A muscle, when it is touched, immediately shuts its shell; and as this action puts it in a state of defence, we conclude that it proceeded from the principle of self-preservation. When the sensitive plant contracts from a touch, it is no more in a state of defence than before; for whatever would have destroyed it in its expanded state, will also do it in its contracted state. We conclude, therefore, that the motion of the sensitive plant proceeds only from a certain property called by physicians irritability; and which, though our bodies possess it in an eminent degree, is a characteristic neither of animal nor vegetable life, but belongs to us in common with brute-matter. It is certain, that an electrified silk-thread shews a much greater variety of motions than any sensitive plant. If a bit of silk-thread is dropped on an electrified metal-plate, it immediately erects itself; spreads out the small fibres like arms; and, if not detained, will fly off. If a finger is brought near it, the thread seems greedily to catch at it. If a candle approaches, it claps close to the plate, as if afraid of it.—Why do we not conclude that the thread in this case is really afraid of the candle? For this plain reason, That its seeming flight is not to get away from the candle, but to get towards the electrified metal; and, if allowed to remain there, will suffer itself to be burnt without offering to stir.—The sensitive plant, in like manner, after it has contracted, will suffer itself to be cut in pieces, without making the least effort to escape. The case is not so with the meanest animal. An hedge-hog, when alarmed, draws its body together, and expands its prickles, thereby putting itself in a posture of defence. Throw it into water; and the same principle of self-preservation prompts it to expand its body, and swim. A snail, when touched,
withdraws itself into its shell; but if a little quicklime is sprinkled upon it, so that its shell is no longer a place of safety, it is thrown into agonies, and endeavours to avail itself of its locomotive power in order to escape the danger. In muscles and oysters, indeed, we cannot observe this principle of self-preservation so strongly, as nature has deprived them of the power of progressive motion: but, as we observe them constantly to use the means which nature has given them for self-preservation, we can have no reason to think that they are destitute of that principle upon which it is founded.
But there is no need of arguments drawn from the inferior creation.—We ourselves are possessed both of the animal and vegetable life, and certainly must know whether there is any connection between vegetation and sensation or not.—We are conscious that we exist; that we hear, see, &c.: but of our vegetation we are absolutely unconscious. We feel a pleasure, for instance, in gratifying the calls of hunger, and thirst; but of the process by which our aliment is formed into chyle, the chyle mixed with the blood, the circulation of that fluid, and the separation of all the humours from it, we are altogether ignorant. If we then, who are more perfect than other vegetables, are utterly insensible of our own vegetable life, why should we imagine that the less perfect vegetables are sensible of it?
To illustrate our reasoning here by an example.—The direction of the roots of the plane-tree mentioned by Lord Kaimes, shews as much sagacity, if we are to look only to the outward action, as can be observed in any motion of the most perfect animal whatever; nevertheless, we have not the least suspicion, either that the tree saw the ground at a distance, or that it was informed of its being there by the rest of its roots. If a wound is made in the body of a man, and a loss of substance is to be repaired, the same sagacity will be observed in the arrangement of the fibres, not only as if they were animated, but they will dispose of themselves seemingly with a degree of wisdom far superior to what we have any idea of; yet this is done without our having the least knowledge either how it is done, or of its being done at all. We have therefore in ourselves a demonstration, that vegetable life acts without knowing what it does: and if vegetables are ignorant of their most sagacious actions, why should we suspect that they have a sensation, let it be ever so obscure, of any of their inferior ones, such as contracting from a touch, turning towards the sun, or advancing to meet a pole?
Thus we may easily give Mr Buffon a reason why we ascribe sensation to an oyster, and none to a vegetable; namely, because we perceive the vegetable do nothing but what is also performed in our own bodies, without our having the least sensation of it; whereas an oyster puts itself in a defensive posture on the approach of danger; and this being an action similar to our own upon a like occasion, we conclude that it proceeds from the same principle of sensation. Here it may also be observed, that though the inferior animals are deficient in the number, they are by no means so in the acuteness of their sensations; on the contrary, though a muscle or an oyster is probably endowed with no other sense than that of feeling, yet this sense is so exquisite, that it will contract upon the slightest touch, such as we would be altogether insensible of.
As to that power of contractility, or irritability, which is observed in some plants; our solids have it, when deprived both of vegetable and animal life: for a muscle, cut out of a living body, will continue to contract, if it is irritated by pricking it, after it has neither sensation nor vegetation.
A very good moral reason may also be adduced why we do not believe vegetables to be endowed with sensation.—Had they been so, we must suppose them to suffer pain when they are cut or destroyed; and, if so, what an unhappy state must they be in, who have not the least power to avoid the injuries daily offered them? In fact, the goodness of the Deity is very conspicuous in not giving to vegetables the same sensations as to animals; and, as he hath given them no means of defence, though we had not been told it by himself, we might have known that he gave them for food to animals; and, in this case, to have endowed them with sensation would have been a piece of cruelty. Though animals without number prey upon one another, yet all of them have some means of defence; from whence we may justly conclude, that their mutual destruction was not an original appointment of the creator, but what he foresaw would happen in a course of time, and which he therefore gave every one of them some means of guarding against. It may no doubt be here objected, that the giving some means of self-defence to every animal cannot be reckoned a sufficient proof that it was not the original design of the Creator that they should be destroyed, seeing these means are not always effectual for their preservation.—This objection, however, cannot be completely obviated without a solution of the question concerning the origin of evil among the works of a perfectly good Being. But whatever difficulty there may be in solving this question, it is certain, that, as some means of self-defence is given to every animal, it has been the original design of the Creator, that, in all cases, one species of animals should not be destroyed at the pleasure of any other species; and as no means of self-defence is given to any vegetable, it is as plain, that they have been destined for a prey to every species of animals that had access to them. Philosophers have insisted much on the necessity of one animal's devouring another, that there might be room sufficient for all; but this, so far from being a system worthy of the divine wisdom, seems to us to be a reflection upon it, as if the author of nature could not have found means to preserve the life of one part of his creatures, without the destruction and misery of the rest. The sacred writings leave us at no loss to see how this carnivorous disposition came in; and, in the next world, this piece of perfection, (as the sanguinary philosophers abovementioned would have it to be), seems to be left out; for there, it is said, "They shall not hurt nor destroy, the lion shall eat straw like the ox, and there shall be no more pain."
When speaking of the food of plants, we took occasion to mention a certain power, totally different from that of attraction or repulsion, by which the food of a plant, after it was attracted, or otherwise brought to it, was assimilated to its substance. This power, which we there distinguish by the name of transmutation, be-
longs in a more eminent degree to animals. The alimentary substance is changed into two kinds of matter. (1.) An excrementitious one, which passes off through the intestines; and (2.) A fluid, which is the direct pabulum of the animal. Different substances, however, are not equally changeable by this process. The human stomach is not capable of acting upon any animal substance till it has lost its vital principle: the stomachs of some animals cannot act upon creatures of their own species: some have an apparatus for grinding their food after it is swallowed, &c. and there are no animals but what are subject to death by taking certain substances into their stomach. Some substances also, though they resist the action of the stomach, and pass unchanged into the system, produce no bad effects. Thus, madder will turn the bones of animals red; rhubarb will communicate its purgative nature to the milk, and its deep yellow colour to the urine.—All these changes, however, seem to belong to the vegetative part of our system: for as every one of them are performed without our knowledge of the manner how; and not only so, but while we are absolutely unconscious of their being done; we can have no reason to suppose, that the animal life, properly so called, is at all connected with them, any farther than as they are at present the means of preserving the creature alive, and making the connexion betwixt the principle of life and this visible creation.
The description, history, and classing of animals, makes not only a considerable, but the most excellent, part of Natural History, known by the name of Zoology. See the article ZOOLOGY.
For particulars relating to different animals, their analogous structure, sagacity, instinct, peculiarities, &c. see COMPARATIVE ANATOMY, INSTINCT, MIGRATION, PAIRING, AMPHIBIOUS, BIRD, FISH, QUADRUPED, &c. SINGING, NIDIFICATION, VIVIPAROUS, OVIPAROUS, &c.