56 Functions of living beings. 57 Motion. General tributed through those parts in a different manner in Phenomena the various tribes of organized beings. In plants, and of Life. in a few of the inferior animals, as the zoophyta, it seems to exist independently in almost every part. A bud, slip, or sucker, torn from the parent plant, and inserted within the bark of another plant, or placed within the earth, in favourable circumstances, vegetates, increases, and in due time becomes a perfect plant, in all respects similar to the parent stock. If a polypus be cut in pieces, each piece lives and grows, till it becomes itself a complete polypus. If a worm be cut in two, so as to leave one part with the head, and the other with the tail, each part becomes a perfect worm, possessing both head and tail. As we ascend, however, in the scale of beings, we find life less equally and independently diffused. A part cut or torn from the body of most animals quickly loses its vitality; but this is lost sooner in some animals than in others. The head of a turtle or a snake is able to bite many hours or even days, after it is severed from the body; and in the former instance, the animal seems for a long time to experience little inconvenience from its loss. The heart of a frog is seen to move many hours after it is cut out. The principal effects of the presence of life appear in the exercise of those functions or actions by which living beings preserve their existence, or reproduce their like. One of the most general properties of organized beings is that susceptibility to motion, which is called irritability, which appears essential to life, and is possessed, in a greater or less degree, by every class of organized beings. The motions of plants are sometimes very remarkable, and approach very nearly to those which take place in animals. The stamina of the cistus helianthemum are seen to move in various directions when the sun shines on them; the leaves of the mimosa pudica (sensitive plant), when touched by the hand, or when irritated by the alighting of an insect on them, immediately contract; the dionaea muscipula (Venus's fly-trap), when a fly touches its leaves, closes the thorny fringes with which they are beset, on the presumptuous insect, and crushes it to death; but the motions of the hedysarum gyrans are the most remarkable of all those that take place in plants. The leaves of this extraordinary vegetable are seen in constant motion through the greatest part of the day, without the intervention of any apparent external impulse; and even when a branch is cut off and kept in water, the motion of the leaves continues for many hours together. All the plants which grow above the earth, expose their leaves and flowers to the warm sunshine, and when situ ated in a place which is supplied by light only from one quarter, they gradually direct their branches towards that part by which the light enters. In stormy weather they retract their leaves, and fold up their flowers, and when confined in the dark, their branches retain the position which they had when last exposed to the light. The motions of many of the lower animals, though sufficiently apparent, are more obscure than those of plants. A muscle or an oyster seems to possess little more motion than is necessary to open and close the valves of its shell, and, no more than plants, has the faculty of conveying itself from place to place. This facalty of locomotion, which in all the higher classes of animals is dependent on the will, will be fully consider- General ed in the second chapter. Phenomena of Life. 58 The function which appears to be most universally diffused in living beings, is digestion, (including nutrition) or that by which the substances intended for their Digestion. nourishment are assimilated to the nature of the body which they enter. This function varies considerably in the different classes. Plants merely attract water from the earth in which they grow, by means of the fibrous parts of their roots, whence it is conveyed by innumerable capillary vessels throughout the whole plant, in which it appears partly to be decomposed, and partly to remain in the state of water, diluting some of the vegetable principles, and thus forming the juices of the plant. In some of the inferior animals, digestion seems to be almost the only function which they are capable of performing. Thus, many of the zoophytes, as the polypi, appear to be almost entirely composed of a stomach, resembling the finger of a glove, into which the aliment is received, the nutritive part extracted, and the excrementitious part thrown out by the same opening. In most other animals, the alimentary canal has two distinct openings, one for the reception of the food, and the other for the ejection of the excrement. By some animals the food is swallowed entire, and digestion is performed by a simple solution or trituration in the stomach; while in others the mouth is furnished with teeth, or other hard parts, capable of reducing the aliment to a pulpy state, in order to render its further digestion more easy and expeditious. In most animals, the food having undergone some change in the digestive organs, is taken up from them by certain very minute vessels, and carried to every part of the body; but in some it appears rather to exude through pores in the sides of the alimentary canal. 59 The function of circulation, by which the fluids are Circulation, constantly moved through every part of the body, is not so general as either of the former functions. In plants there is no proper circulation; for although there are numerous vessels by which water enters into the substance of the plant, and in which the peculiar juices of the vegetable move, the motions of these fluids are not uniform, and do not tend towards one centre. The same defective circulation appears in many of the inferior animals, as in zoophytes and inseets. As we rise, however, to the higher classes, we find a perfect circulation. In these there is always a peculiar organ from which the fluids are conveyed to the rest of the body, and to which they again return in a perpetual round. In some animals this central organ is single, while in others it consists of two similar organs joined together, from one of which the whole of the fluids proceed through one particular organ in a lesser circulation, and thence return to the other part, before they are distributed to the general system. 60 All organized beings require more or less the presence Respiraof atmospheric air for their subsistence, or at least for tion. the due performance of the vital functions. In some, the agency of this fluid is conveyed merely by pores upon the surface; as in plants, in which the leaves absorb the air; and in several of the inferior animals, as insects and worms, over the surface of whose bodies are distri buted numerous openings, by which the air enters. In animals of the higher orders there are peculiar organs called of Life. General called lungs or gills, through which air, or water conPhenomena taining air, enters, and from which its beneficial influence is imparted to the fluids which are circulating through them. In general, these beings exist for a very short time, when deprived of atmospheric air, or when the element in which they live is deprived of oxygen; but in some of the lower classes of animals the absence of oxygen is much less injurious; and there are instances of reptiles in particular having been preserved in a state susceptible of life and motion, while buried for many years in the heart of a tree, or in the middle of a block of stone. Respiration, then, though in general necessary to the continuance of vitality, may, in many tribes of organized beings, be suspended for a considerable time, without the principle of life being entirely destroyed. στ Reproduction. A function equally general, and equally indispensible with that of digestion, and one which forms another characteristic of living beings, is the function of regeneration, a function more peculiarly necessary, as all organized beings, though capaple of resisting for a consider able time the operation of external agents, tend ultimately to corruption and decay; and as they cannot, like inorganic matter, be regenerated by a reunion of their component principles, it was necessary that they should possess the capacity of producing, while in existence, a creature similar to themselves, to supply their place in the scale of being. It has been a very general opinion among naturalists, that all living beings, both plants and animals, originate from seeds or eggs produced by the parent. This, although very generally true, is not a universal fact. Most plants, indeed, with which we are acquainted, appear capable, in their natural state, of producing seeds, which form the embryo of a future plant. But in a great many of them new plants are obtained from buds, slips, or suckers, furnished by the parent. In some animals too, as the polypi, reproduction may be effected by dividing the parent into several pieces; and even the natural generation of these animals is performed by protuberances which grow from the body of the parent, and seem to drop off spontaneously, when capable of an independent existence. There are two striking differences in the manner by which living beings are generated. In some, two distinct sets of organs are necessary, and by the mutual action of these generation is effected; while in others, as in the instances we have mentioned of the polypus, this act of copulation appears to be unnecessary. Almost all plants possess distinct sexual organs, and in most both male and female organs are situated in the same individual. In these plants the female ovum is impregnated by a very fine powder, which is contained in part of the male organs, and is applied to those of the female. We are fully convinced of the necessity of the vegetable copulation, by observing that the females of those plants which have the sexual organs situated in distinct individuals are not capable of producing fruit, or a least do not produce this in perfection, if they are excluded from the influence of the male; and that an artificial impregnation may be brought about by bringing the male and female organs in contact. Many animals are hermaphrodite; and among these the individuals of some species generate without the assistance of another individual of the same species. This appears to be the case with the bivalve shell-fish. Others again, as snails, and General most of the mollusca, which crawl upon the earth, copu- Phenomena late reciprocally, or each individual performs the dou-of Life. ble office of male and female. In most animals, however, the sexes are distinct, and probably a real hermaphrodite in the superior classes never existed. Another striking difference with respect to generation in animals is the more or less perfect state in which they bring forth their young. A large propertion of animale, among which are the insect tribe, fi-hes and birds, produce eggs, which are afterwards hatched by the heat of the parent, or by that of the sun. Other classes again, as some of the amphibia, and the whole of the mammalia, carry their young for a certain time within an organ destined for that purpose, from which they are excluded in the state of perfect animals. 62 The last function which we shall here notice, is sen- Sensation. sation. This appears to be less general than any which we have hitherto mentioned. It has indeed been supposed by many philosophers and naturalists, that plants possess a degree of sensibility; and this opinion has been lately avowed and strenuously supported by the elegant but enthusiastic author of the Botanic Garden, and the Loves of the Plants. That plants possess a suceptibility of receiving impressions, and in consequence of that of being roused into action by external stimuli, we shall readily admit, and shall hereafter assign to this susceptibility its due importance; but as there is no reason to believe that it ever produces sensation, we must not confound it with the sensibility of animals; nor is the difficulty of explaining some of the functions of vegetables, without resorting to the hypothesis of a vegetable sensorium, a sufficient reason for investing them with this faculty. It has even been doubted whether some of the inferior animals, as the zoophytes, possess this function, as nervous fibres have not yet been detected in their organization. It is probable, that there is a regular gradation in the tribes of organized beings with respect to sensation, as well as the other functions; and though we have not been able to discover all the links of this chain, these will probably, as our knowledge of nature increases, come more into view, and we shall then be able to reconcile many circumstances which we cannot at present comprehend. With respect to the varieties that take place in the number and degree of the external senses, as possessed by the various classes of animals, we may refer the reader to what has been said on that subject in the first chapter of the comparative part of the article ANA TOMY. 63 The duration of life is exceedingly various. We Duration of know that there are animals which live but a few hours, life. as the insects called ephemera; and that others, as the elephant, the raven, and the pike, may exist for a century. The term of life allotted to plants is also various; some live only for a year, and are hence called annual plants; others exist for two years, and are called biennial plants; while a few surpass in longevity any thing with which we are acquainted in animated nature. Thus, the oak is said to require 100 years, in order to acquire its full maturity; to retain its perfect vigour for the like term, and to complete at least a third century before it entirely decays. The chesnut is a still more remarkable instance of vegetab e longevity. The account of the gigantic chesnut on Mount Etna, given General by Brydone and other travellers, which has existed for Phenomena many centuries, must be familiar to most of our readers. of Life. We have hitherto considered life as displayed in the exercise of functions; but it may exist independently of this exercise, or it may lie dormant for a considerable time, till called into action by particular circumstances. Every one knows how long a seed or an egg, when excluded from heat, air, and moisture, will retain the faculty of producing a plant or an animal. The only proof we have, that this faculty still exists, is, that when we place the seed or the egg in circumstances favourable to the developement of the embryo which it contains, the process of generation goes on, till the plant or the animal is excluded. We know also, that after an organized being has commenced the exercise of its functions, this exercise may cease for a time, or at least become almost imperceptible, while yet the vital power shall remain susceptible of reviving its activity at a future period. We then say that the animal or vegetable is in a torpid state. On this part of the history of life we shall not enter at present, but shall defer the consideration of it till we come to treat of sleep and death. The above is a hasty comparative sketch of the functions, exercised by the various tribes of organized beings. It is sufficient to show, that there is in these beings a vital power which completely distinguishes them from brute or inorganic matter. 64 Cause of life. A question which naturally arises in every thinking mind is, What is the essence of life, or on what does it depend? Though we profess ourselves unable to answer this question in a satisfactory manner, and believe that all who have hitherto attempted to do so, have failed in their attempts, it may be acceptable to most of our readers to know the opinions of the most respectable writers on this abstruse subject. These, therefore, we shall briefly state. 65 Opinions These opinions have chiefly rested on the question, respecting whether life be an independent, immaterial principle, or the vital merely a physical or chemical modification of matter. principle. We have already, in the historical view which we have given of the progress of physiology, mentioned some of the more remarkable doctrines respecting the principle of life that have been delivered prior to the 18th century; we shall here, therefore, only mention those which have been maintained since that time. 66 John Hun ser. 67 Goodwin, Mr John Hunter, in his valuable treatise on the blood, supposes the principle of vitality to exist in that fluid, or that the blood has life; and has founded this doctrine chiefly on the following proofs. First, It unites living parts, when it is effused between them. Secondly, It becomes vascular like other living parts; its temperature as it flows from the vessel, is always equal in the most opposite temperature in which the body can bear exposure. Thirdly, It is capable of being acted upon by a stimulus, as is the case when it coagulates. Fourth, Paralytic limbs, though deprived of motion and sensation, are yet nourished and preserved alive by the blood circulating through them. Mr Hunter's idea of the vitality of the blood is merely the revival of one of the oldest physiological doctrines on record; namely, that delivered to the Israelites by Moses, that in the blood is the life of an animal. Dr Goodwin, in his work on the connection of life with respiration, is of opinion, that the heart is the great seat of the principle of life in all the more perfect aniVOL. XVI. Part II. mals; and that the contractions of the heart with the General ordinary stimulus is the only mark of the presence of this Phenom na principle; that when the heart contracts under such of it. circumstances, the body is alive; when not, it is dead. Life he therefore defines to be the faculty of propelling the fluids through the circulatory system. According to him, the external concomitant circumstances which operate upon the body in health are heat and respiration, which excite the vital principle to action; and whenever the functions of an animal are suddenly suspended, and the body puts on the appearance of death, it is always in our power to determine whether it be really dead, by restoring the temperature, and by inflating the lungs with proper air. He is of opinion, with some others, that there are no means of determining the absolute deprivation of the vital principle but by the presence of putrefaction. 63 It has lately become fashionable to consider life as the consequence of certain chemical changes, which are going on in the body; an opinion which is chiefly supported by Hufeland, Girtanner, and Humboldt. According to Hufeland, life is a chemico-animal Hufeland. flame, to the production of which oxygen is absolutely necessary, and the vital power is the most general and powerful of all the powers of nature. He considers it as the cause of organization, and as possessing the following properties. 1. It has a greater affinity to some organized bodies than to others; thus, the polypus may be cut in pieces without being divested of it, and a decapitated tortoise or a frog deprived of its heart will live a long time after; whilst to the human body, or a quadruped, it would be instant death. According to this physiologist, it is a general rule, that the stronger the affinity between life and an organized being, the more imperfect is the animal; hence the zoophytes, whose whole organization consists in a mouth, a stomach, and a gut, have a life exceedingly tenacious, and difficult to be destroyed. 2. It is in greater quantity in some organized bodies than in others. In general, cold-blooded animals live longer than those with warm blood. 3. It frees bodies from the chemical laws of inanimate matter, and transfers the component parts of a body from the physical or chemical to the organic or living world. 4. It prevents putrefaction, for no organized body can putrefy unless deprived of life. ნი Humboldt is of opinion, that the degree of vitality Humboldt depends upon the reciprocal balance of the chemical affinities of all the elementary parts of which the animal body is composed. 70 Some physiologists of the present day deny the exist- Cuvier. ence of the vital principle altogether, "The idea of life (says Cuvier), is one of those general and obscure ideas produced in us by observing a certain series of phenomena, possessing mutual relations, and succeeding each other in a constant order. We know not indeed the nature of the link that unites these phenomena, but we are sensible that a connection must exist; and this conviction is sufficient to induce us to give it a name, which the vulgar are apt to regard as the sign of a particular principle, though in fact that name can only indicate the totality of the phenomena which have occa、 sioned its formation." Dr Ferriar, in his observations concerning the vital Ferriar principle, thinks, that some direct arguments may be 3 N brought General brought against the general supposition of an independPhenomena ent living principle. These arguments he divides into of Life, two kinds, viz. refutations of the general proofs offered in support of the vital principle; and instances of the direct influence of the mind and brain over what is termed the independent living principle. The great proofs for the support of a vital principle, are the contraction of muscles separated from the body on the application of stimulants; the performance of the vital and involuntary motions without any exertion or even consciousness of the mind, and the birth of full grown foetuses destitute of a brain. In all these cases, something is alleged to operate, independently of the mind, in producing muscular motion. Dr Ferriar, in answer to the first argument drawn from the contraction of separated muscles, affirms, it may be said, 1st, That the power of contraction, in a separate muscle, is lost before putrefaction takes place, i. e. before the destruction of its texture; but if its vitality depended on its texture, this ought not to happen. 2dly, The power of contraction, in a separated muscle, is strongest upon its first separation, and becomes weaker by degrees; therefore, the contracting power seems to have been derived from some source from which it is detached by the excision of the part. 3dly, Irritation of the medulla oblongata, or of the nerves supplying particular muscles, occasions stronger contractions than irritation of the muscles themselves; and Dr Whytt furnishes an experiment on a frog, directly proving, that the action of separated muscles depends upon the nervous energy. 4thly, Dr Haller himself is obliged to make on this subject a concession sufficient to destroy his favourite hypothesis of the vis insita. 5thly, When a paralytic limb is convulsed by the electric shock, the motion never takes place without the patient's consciousness. In this case there is no distinction between the vital principle, and that exertion which in voluntary motion is always attributed to the mind. See Chap. iii. In answer to the second argument, in favour of a vital principle, drawn from the performances of the vital and other involuntary motions, Dr Ferriar contents himself with only observing, that, allowing the organs of those motions to be supplied with nervous energy, their motions may be very well accounted for by the stimulus of their contained fluids. The force of the third argument, drawn from the want of a brain in full-grown fœtuses, is taken off by Dr Whytt, who remarks, that as the heart is sometimes wanting in full-grown foetuses, the argument would equally prove, that the heart is not necessary for the continuance of circulation, as that the brain is not necessary to the support of the system. Accordingly, fœtuses born without a brain do not, in general, survive birth. Besides the general supposition of an independent living principle, an inference has been drawn from facts, of a nervous energy independent of the brain. By this term is meant, that condition derived from the brain to different parts of the body, by means of which they become capable of motion. To show, by direct proof, that there is no independent vital principle, Dr Ferriar observes, 1. That it is justly urged by Dr Monro against the doctrine of the vis insita, that there is too much design in the actions of different muscles, affected by dif ferent stimuli, to be the effect of mere mechanism. General Thus, when the hand or foot is burnt, or otherwise sud- Phenomena denly injured, the muscles on the part immediately sti- of Life. mulated are not thrown into action, nor the muscles on the side irritated, but their antagonists contract immediately and strongly. Now, if the instantaneous action be in this case chiefly produced by an effort of the mind, the supposition of a distinct vital principle is superfluous: if it be said to be produced by a living power independ ent of the mind, then there must be a rational power in the body independent of the mind, which is absurd. 2. The state of the vital and involuntary motions is considerably affected by the state of the mind, which equally disproves the existence of a separate vital principle, and proves the dependence of the nervous energy upon the brain. 3. Madness, it is well known, is frequently produced by causes purely mental, and in persons apparently in good health; and, as the patient's sensibility to very powerful stimuli is much diminished in maniacal cases, they afford another proof of the subordination of the nervous energy. 4. It has been observed, that in paralytic cases, motion is frequently destroyed, while sense remains. As the cause of palsy almost always resides in the brain, this fact appears equally inexplicable on the opinion of a distinct living principle, or of a ner vous energy, independent of the brain. 5. When serves are regenerated, after being cut through, sensation and voluntary motion are not always restored to the parts beneath the division: the restoration was never made in Dr Monro's experiments. But, on the supposition of a distinct nervous power, the nerve, after its reunion ought to resume all its offices. 6. Dr Whytt asserts, that when the spinal marrow of a frog is destroyed, after decollation, no contraction can be excited in the limbs, by cutting or tearing the muscles. are the facts and arguments which Dr Ferriar brings against the opinion of a distinct living principle; and he thinks, that their investigation appears to lead us back to the brain as the source of sensibility and irritability. Such In the life of Dr John BROWN, we have given an ac- Rush. count of the doctrine, of life being a forced state. This doctrine appears to have been first delivered by Dr Cullen, though he afterwards retracted it. Of late Dr Rush of Philadelphia, in his Lectures on Animal Life, has advanced many arguments in favour of this doctrine. He includes, in animal life, three properties as applied to the human body, viz. motion, sensation, and thought; and these, when united, compose perfect life. It may exist without thought or sensation; but neither sensation nor thought can exist without motion. He affirms, that the lowest degree of life exists even in the absence of motion. He first considers animal life as it appears in the waking and sleeping state, in a healthy adult; and afterwards inquires into the modification of its causes in the foetal, infant, youthful and middle states of life, in certain diseases, in different states of society, and in different animals, and lays down the following propositions: 1. Every part of the human body, the nails and hair excepted, is endued with sensibility or excitability, or with both. 2. The whole body is so formed and connected, that impressions made in the healthy state upon one part 72 General excite motion, or sensation, or both, in every other part Phenomena of the body, of Life. sible. 73 3. Life is the effect of certain stimuli acting upon the sensibility and excitability, which are extended in different degrees to every external and internal part of the body; and these stimuli are as necessary to its existence as air is to flame. He continues to observe, that the action of the brain, the diastole and systole of the heart, the pulsation of the arteries, the contraction of the muscles, the peristaltic motion of the bowels, the absorbing power of the lymphatics, secretion, excretion, hearing, seeing, smelling, taste, and the sense of touch, even thought itself, are all the effects of stimuli acting upon the organs of sense and motion. These have been divided into external and internal. 1. The external are light, sound, colours, air, heat, exercise, and the pleasures of the senses. 2. The internal stimuli are food, drinks, chyle, blood, tension of the glands which contain secreted liquors, and the exercise of the faculties of the mind. Life, therefore (according to the hypothesis of Rush), even thought itself, is merely a quality residing in the component parts of a material system, dependent upon a peculiar organization, by which it is enabled to act, or in some ways to move on being stimulated or excited. Hence life can never be inherent in a simple uncom pounded substance, nor in a particle of animal matter; and if the stimulus be withheld from a living system beyond a given time, all motion, sensation, and thought, must necessarily be extinguished. Vital prin- Instead of one vital principle, some physiologists have ciple suppo- supposed the existence of several in the same body; and sed by some from the phenomena that take place in some organized to be divi- beings, as the reunion of parts that had been separated, the reproduction of others that have been lost, and the separate existence of the divided parts of some worms and zoophytes, it was formerly the opinion of a celebrated lecturer on anatomy, that the vital principle was really divided. From more considerate and extensive inquiry, however, he is now of opinion, that the irritability on which these phenomena depend, is never the direct or immediate operation of the vital principle, but only the consequence of its operation; and in no case exclusively the consequence, but the consequence likewise of other operations proceeding from a number of different causes: and hence it is that a vital principle may often exist where it cannot operate in a sensible manner, from the want of auxiliaries; and hence it is, likewise, that its effects may often be continued, at least for a while after its departure. With regard to the portions of plants and polypi that continue to live in a separate state, assume the form of their respective species, and propagate their kind, they will be found, on a close examination, to have been originally complete systems; many of the plants and many of the polypi that were usually considered as simple individuals, not constituting one animated system, but rather a congeries of animated systems,-a congeries, too, which after all is nothing more than a species of society, + Barclay where animated beings are associated together for mutual protection; such as we see among men in a city; among bees in their cells, which, in point of form, are similar to plants +. on Muscular Motions, p. 265. As all living beings are so related to each other, and 74 Necessity to the inanimate objects of nature, as to be capable of of sensibideriving benefit, or receiving injuries, from the one or lity to orgafrom the other; it seems necessary that they should pos- nized besess the faculty of perceiving the proximity of the be-ings. neficial or injurious object, that they may avail themselves of the benefit which it holds out, or avoid the danger which it threatens. Accordingly, we find that all organized beings enjoy in some degree the capacity of receiving impressions, which we think is proved by the motions which take place in them when affected by external agents. When a plant expands its flowers to the sun, or turns, as it were, its back to the blast; when it stretches out the fibres of its roots to imbibe the distant moisture, or directs its branches to the only chink by which it can receive the light of day; we think these motions are the consequence of that capacity of receiving impressions, or of being roused to action by stimuli; we think that this may be conceded, without having recourse to the influence of mind, or even the medium of a nervous system; we do not believe that the grass we crush beneath our feet is sensible of pain, nor do we suppose with the poet, that "E'en the poor beetle that we tread on 75 but we are of opinion, that even in the lowest tribes Sensitivity. there is a degree of that faculty, which in the higher orders of animals we call sensibility, and which we shall here, after a lecturer on the animal economy in London, denominate sensitivity. This inferior degree of the sensitive faculty we shall suppose to be possessed by plants, zoophytes, and animalcules, or those organized beings in which we can perceive no marks of a nervous system; while we shall confine the term sensibility to all other classes of animals. These faculties we consider as qualities of living bodies, while we regard sensation, like perception, as a quality of mind. We leave it to the metaphysician to mark the line of distinction between sensibility and sensation, and to show how the one arises from the other. See METAPHYSICS, Part I. chap. 1. 16 The organs of sensation consist of the brain proper- Nervous ly so called, the cerebellum, the medulla oblongata, the system. spinal marrow, the nerves, and ganglia; together forming what is called the nervous system. These parts in the human body have been described under ANATOMY. For an account of these organs in the inferior animals, we must refer to the lectures of Cuvier, vol. ii. or the Comparative Anatomy of Blumenbach. In respect of sensibility the animal is only passive; but when sensation is produced, he becomes active, in as much as the organs of the external senses are then brought into action. It is by means of these senses that the animal receives intelligence from without. We shall therefore examine these before we mention the phenomena of sensation in general. |