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nary section of the Levitical code; a doctrine, indeed, of no new invention, even at that early period, but probably derived expressly from the ritual of the higher patriarchs, if we may be allowed to appeal to a similar belief and a similar practice among the Parsees, Hindoos, and other oriental nations of very remote antiquity, who seem rather to have drawn this part of their ceremonial directly from the law or tradition of the patriarchs, than indirectly from that of the Jews,
Among the Greeks and Romans, were the authority of the poets to be of any avail, we should imagine that this hypothesis never ceased to be in reputation : for the moppupeos bávaros, or purple death, of Homer, and the purpurea anima, or purple life, of Virgil (phrases evidently derived from this theory), are commonplace terms amid all of them: but the real fact is, that among the philosophers, we do not know of more than two, Empedocles and Critias, who may be fairly said to have embraced it.
In modern times, however, this hypothesis has again dawned forth, and risen even to meridian splendour, under auspices that entitle it to our most attentive consideration. Harvey, to whom we are indebted for a full knowledge of the circulation of the blood, may be regarded as the phosphor of its uprising ; Hoffman speedily became a convert to the revived doctrine; Huxham not only adopted it, but pursued it with so much ardour, as, in his own belief, to trace the immediate part of the blood in which the principle of life is distinctly seated, and which he supposed to be its red particles. But it is to that accurate and truly original physiologist, Mr. John Hunter, that we can only look for a fair restoration of this system to the favour of the present day, or for its erection upon any thing like a rational basis. By a variety of important experiments, this indefatigable and accurate observer succeeded in proving incontrovertibly that the blood contributes in a far greater degree, not only to the vital action, but to the vital material of the system, than any other constituent part of it, whether fluid or solid. But he went beyond this discovery, and afforded equal proof, not only that the blood is a means of life to every other part, but that it is actually alive itself. “ The difficulty,” says he, "of conceiving that the blood is endowed with life, while circulating, arises merely from its being a fluid, and the mind not being accustomed to the idea of a living fluid.—I shall endeavour,” he continues, " to show that organization and life do not in the least depend upon each other; that organization may arise out of living parts and produce action, but that life can never arise out of or produce organization."*
This is a bold speculation, and some part of it is advanced too hastily: for instead of its being true, "that life can never arise out of or produce organization,” the most cursory glance into nature will be sufficient to convince every man that organization is the ordinary, perhaps the only, means by which life is transmitted ; and that wherever life appears, its tendency, if not its actual result, is nothing else than organization. But though he failed in his reasoning, he completely succeeded in his facts, and abundantly proved that the blood itself, though a fluid and in a state of circulation, is actually endowed with life : for he proved, first, that it is capable of being acted upon and con, tracting, like the solid muscular fibre, upon the application of a stimulus ; of which every one has an instance in thất cake or coagulum into which the blood contracts itself when drawn from the arm, probably in consequence of the stimulus of the atmosphere. He proved, next, that in all degrees of atmospherical temperature whatever, whether of heat or cold, which the body is capable of enduring, it preserves an equality in its own temperature; and in addition to this very curious phenomenon, he proved also, that a new-laid egg, the vessels of which are merely in a nascent state, has a power of preserving its proper temperature, and of resisting cold, heat, or putrefaction, for a considerable period longer than an egg that has been frozen, or in any other way deprived of its vital principle. Thirdly, he proved, in the instance of paralytic limbs, that the blood is capable of preserving vitality when every
* Hunter on the Blood, p. 20
other part of an organ has lost its vital power, and is the only cause of its not becoming corrupt. Fourthly, that though not vascular itself, it is capable, by its own energy, of producing new vessels out of its own substance, and vessels of every description, as lymphatics, arteries, veins, and even nerves.* Finally, he proved, that the blood, when in a state of health, is not only, like the muscular fibre, capable of contracting upon the application of a certain degree of appropriate stimulus, but that, like the muscular fibre also, it is instantly exhausted of its vital power whenever such stimulus is excessive; and that the same stroke of lightning that destroys the muscular fibre, and leaves it flaccid and uncontracted, destroys the blood, and leaves it loose and uncoagulated.
Important, however, as these facts are, they do not reach home to the question before us. They sufficiently establish the blood to be alive, but they do not tell us what it is that makes it alive : on the contrary, they rather drive us into a pursuit after some foreign and superadded principle; for that which is at one time alive, and at another time dead, cannot be life itself.
The next theory, therefore, to which I have adverted, undertakes to explain in what this foreign and superadded principle consists. SOME EXQUISITELY SUBTLE GAS Or AURA—some fine, elastic, invisible fluid, sublimed by nature in the deepest and most unapproachable recesses of her laboratory, and spirited with the most active of her energies. An approach towards this hypothesis is also of great antiquity; for it constituted one of the leading features of the Epicurean philosophy, and is curiously developed by Lucretius in his poem on the Nature of Things. According to him, it is a gas or aura, for which in his day there was no name, diffused through every part of the living fabric, swifter and more attenuate than heat, air, or vapour, with all which it concurs in forming the soul or mind as its chief elementary principle:
Far from all vision this profoundly lurks,
But it is to the astonishing discoveries of modern chemistry alone that we are indebted for any fair application of any such fluid to account for the phenomena of life.
Among the numerous gases which modern chemistry has detected, there are three which are pre-eminently entitled to our attention, though they seem to have been glanced at by the Epicureans: caloric, or the matter of heat, chiefly characterized in our own day as a distinct substance, by the labours of Dr. Black and Dr. Crawford; oxygen, or the vital part of atmospheric air, first discovered by Priestly, and explained by Lavoisier; and the fluid which is collected by the Voltaic trough, and which is probably nothing more than the electric fluid under a peculiar form.
Of these, caloric, as a distinct entity, was detected first. It was found to be a gas of most astonishing energy and activity, and, at the same time, to be of the utmost consequence to the living substance; to exist manifestly wherever life exists, and to disappear on its cessation. It was hence conceived to be the principle of life itself.
But oxygen began now to start into notice, and the curious and indispensable part it performs in the respiration, as well as in various other functions of both animal and vegetable existence, to be minutely explored and ascertained, and especially by the microscopic eye of M. Girtanner. The genius of Crawford fell prostrate before that of Lavoisier. Oxygen was now regarded as the principle of life, and heat as its mere attendant or handmaid.
About the year 1790, Professor Galvani, of Bologna, accidentally discovered • Dr. Munro has proved, that the limb of a frog can live and be nourished, and its wounds heal, without
† Nam penitus prorsum latet hæc natura, subestque ;
Atque anima est animæ proporro totius ipsa.
De Rer. Nat. iii. 274.
that the crural nerve of a frog, which had been cut up for his dinner, contracted and became convulsed on the application of a knife wetted with water; and following* up this simple fact, he soon discovered also, that a similar kind of contraction or convulsion might be produced in the muscles of other animals, when in like manner prepared for the experiment, not only during life, but for a considerable period after death; and that in all such cases a fluid of some sort or other was either given to the contracting body or taken from it. And Professor Volta, about the same period, succeeded in proving that the fluid thus traced to be given or received was a true electric aura ; that it might, in like manner, be obtained by a pile of metallic plates, of two or three different kinds, separated from each other by water, or wetted cloth or wadding; and be so accumulated by a multiplication of such plates, as to produce the most powerful agency in all chemistry. It is not necessary to pursue this subject any farther. Every one in the present day has some knowledge of Galvanism and Voltaism; every one has witnessed some of those curious and astonishing effects which the Voltaic fluid is capable of operating on the muscles of an animal for many hours after death: and it only remains to be added, that since the discovery of this extraordinary power, oxygen has in its turn fallen a sacrifice to the Voltaic fluid, and this last has been contemplated by numerous physiologists as constituting the principle of life; as a fluid received into the animal system from without, and stimulating its different organs into vital action. “ The identity," says Dr. Wilson Phillip, “ of Galvanic electricity and nervous influence is established by these experiments.”
The result of the whole appears to be, that neither physiology nor chemistry, with all the accuracy and assiduity with which these sciences have been pursued of late years, has been able to arrest or develope the fugitive principle of life. They have unfolded to us the means by which life, perhaps, is produced and maintained in the animal frame, but they have given us no information as to the thing itself; we behold the instrument before us, and see something of the fingers that play upon it, but we know nothing whatever of the mysterious essence that dwells in the vital tubes, and constitutes the vital harmony.
It seems to be on this account, chiefly, that the existence of such a princi. ple as a substantive essence has been of late years denied by MM. Dumas, Bichat, Richerand, Magendie, and, indeed, most of the physiologists of France; whose hypothesis has been caught up and pretty widely circulated in our own country, as though nothing in natural science can be a fair doctrine of belief, unless its subject be matter of clear developement and explanation. But this uncalled-for skepticism has involved these philosophers in a dilemma from which it seems impossible for them to extricate themselves, and which we shall have occasion to notice more fully hereafter: I mean the existence of powers and faculties without an entity or substantial base to which they belong, and from which they originate. They allow themselves to employ the term, and cannot, indeed, do without it; but after all they mean nothing by it. “No one in the present day,” says M. Richerand, “contests the exISTENCE OF A PRINCIPLE OF LIFE, which subjects the beings who enjoy it to an order of laws different from those which are obeyed by inanimate beings; by means of which, among its principal characteristics, the bodies which it ANIMATES are withdrawn from the absolute government of chemical affinities, and are capable of maintaining their temperature at a near degree of equality, whatever be that of the surrounding atmosphere. Its ESSENCE is not designed to preserve the aggregation of constituent molecules, but to collect other molecules which, by assimilating themselves to the organs that ir vivities, may replace those which daily losses carry off, and which are employed in
• It is a singular fact, that this identical discovery was not only made, but completed in all its bearings, and by the same means of a recentiy-dissected frog, by Dr. Alexander Stuart, physician to the queen, in 1732, though no advantage was taken of it. A minute account of Dr. Stewart's experiments is given in the Phil. Trans. for 1732. Soe the author's Study of Medicine, vol. ii. p. 29, 2 edit.
repairing and augmenting them."* Yet, when we come to examine into the subject more closely, we find that all these terms, so expressive of a specific being and distinct reality-this ESSENCE that VIVIFIES and ANIMATES, has neither being, nor essence, nor vivification, nor animation, nor reality of any kind; that the whole of these expressions are metaphysical ; and that the word VITAL PRINCIPLE is not designed to express a distinct being, but is merely an abridged formula, denoting the TOTALITY OF POWERS ALONE which animate living bodies, and distinguish them from inert matter, the TOTALITY OF PROPERTIES and Laws which govern the animal economy.t So that we have here not only the employment of terms that have no meaning, but properties and laws, powers and principles, without any source,-a superstructure without a foundation,-effects without a cause.
But what is this curious and delicate instrument itself ?-this machine that so nicely responds to the impressions communicated to it, and visibly enve. lopes so invisible a constituent ?
It is not my intention in this series of pular study to enter into any mi. nute history of the animal frame, but shall confine myself to those general views of it which are requisite to show by what means it is operated upon by the delicate powers we have just contemplated, and the more curious phenomena which result from such an impulse.
The animal frame, then, is a combination of living solids and fluids, duly harmonized, and equally contributory to each other's perfection. The principle of life, whatever it consists of, exists equally in both; in some kinds in a greater, in others in a less degree. In the Huids, Mr. Hunter has traced it down to their first and lowest stage of existence, for he has traced it in the chyle ;£ and there are evident proofs of its accompanying several of those which are eliminated from the body; in the blood it is found, as we have already had occasion to notice, in a high degree of activity, and probably in a still higher in the nervous fluid.
In the solids it varies equally. There are some in which it can scarcely be traced at all, excepting from their increasing growth, as the cellular membrane, and the bones; in others, we find a perpetual internal activity, or susceptibility to external impressions. But it is in those irritable threads or fibres which constitute the general substance of the muscles or flesh of an animal, that the principle of life exerts itself in its most extraordinary manner, and which it more immediately, therefore, falls within the scope of the present lecture to investigate.
The muscle of an animal is a bundle of these irritable fibres, or soft, red, cylindrical, and nearly inelastic threads, formed out of a substance which the chemists, from the use to which it is applied, denominate fibrine; and which, when examined microscopically, are seen to divide and subdivide, as far as the power of glasses will carry the eye, into minuter bundles of fibrils, or still smaller threads, parallel to each other, and bound together by a delicate cellular web-work, obviously of a different nature. They are uniformly accompanied through their course by a number of very minute nerves, which are chords or tubes that originate from the brain, and branch out in every direction, either immediately from the brain itself, or from some part of the spinal marrow, which is a continuation of this organ; by which means a perpetual communication is kept up between the sensorium and the remotest part of the body, as we shall have farther occasion to notice hereafter. Upon the
*“ Personne aujourd'hui ne conteste ISTENCE D'UN PRINCIPE DE VIE qui soumet etres qui en jouissent à un ordre de lois differentes de celles auxquelles obéissent les êtres inanimés, force à laquelle on pourroit assigner, comme principaux caractères, de soustraire les corps qu'ELLE ANIME. á l'empire absolu des affinités chimiques, auxquelles ils auroient tant
de tendance à ceder, en virtu de la multiplicité de leurs elemens; et de maintenir leur température d un dégré presque égal,
quelle que soit d'ailleurs celle de l'atmosphere. Son ESSENCE n'est point de conserver l'aggregation des molécules constitutives, mais d'attirer d'autres molécules qui, s'assimilant aux organes qu’LLLE VIVIFIE. remplacent celle qu'entrainent les pertes
journalières, et sont employées à les nourrir et à les accroître.”—Nouveaux Eleméns de Physiologie, tom. i. p. 81. Paris, 8vo. 1804.
"Le mot de PRINCIPE VITAL, force vitale, &c. n’exprime point un être existant par lui-même, et independammont des actions par lesquelles il se manifeste : il ne faut l'employer que commune formule abrégee dont on se sert pour désigner l'ensemble des forces qui animent les corps vivans et les distinguont de la matière inorto : l'ensemblo des propriétés et des ldx qui régissent l'économie animala."-Ib. p. 80. On the Blood, p. 91.
0 Series 1. Leotare xv.
application of any irritating or stimulating power, these fibres immediately contract in their length, and upon the cessation of such power return to their former state of relaxation: and it is chiefly by this curious contrivance that the animal system is enabled to fulfil all its functions. The stimuli by which the fibres, whether of motion or of sensation, are roused into action, are perhaps innumerable in the whole; but a few general classes may easily be devised to comprise all those by which they are ordinarily affected. And while by an admirable diversity of construction, some sets of fibres are only affected by some sets of stimuli, other sets are only affected by others; and in this manner all the organs are compelled, as it were, to execute the different offices intrusted to thein, and no one interferes with that of another. Thus the fibres of the external senses are affected by external objects; they contract and give notice of the presence and degree of power of such objects to the brain, through the medium of the nerves, which, as I have just observed, always accompany them, and which either terminate in or arise from that organ: but while the irritative and sensitive fibres of the ear are excited only by the stimulus of sound, and have no impression produced upon them by that of light, those of the eye are excited only by the stimulus of light, and remain uninfluenced by that of sound: and so of the other organs of external
And hence we obtain a knowledge of one set or class of stimuli, which from their acting upon the organs of sense, are called sensitive stimuli, and the motions to which they give rise sensitive motions.
Again, the very substances naturally introduced into many of the muscular organs of the body, and especially the hollow muscles, are sufficient to excite them to a due performance of their functions: thus, the lungs are excited to the act of respiration by the stimulus of the air we breathe, the stomach to that of digestion by the stimulus of the food introduced into it; so the heart and blood-vessels are excited by the stimulus of the blood; and the vessels that carry off the recremental materials by the different stimuli which these materials contain in themselves. We hence obtain another class of stimuli, which are denominated stimuli of simple irritation; and the motions they produce, simple irritative motions, or motions of irritation.
But the sensory, or brain, which thus receives notice generally, or is impressed upon by the different actions that are perpetually taking place all over the system, through the medium of its own ramifications, or nerves, that uniformly acccompany the irritable fibres, in many instances originates motions, and thus proves a stimulus in itself. All voluntary motions are of this kind; the will, which is a faculty of the sensorium, being the exciting cause, and thus giving birth to a third class of stimuli, and of a very extensive range, which are called stimuli of volition. While habit or association becomes, in a variety of instances, a sufficient impulse to other motions, and thus constitutes a fourth class; which are hence named associate stimuli, or stimuli of association.
But though the muscular fibre is, perhaps, more irritable than any other part of the system, the principle of irritability and a fibrous structure are by no means necessarily connected; for, while the cellular membrane is fibrous but has no irritability whatever, the skin is not fibrous but is highly irritable.
Hence solids and fluids are equally necessary to the perfection of the living system. Food, air, and the ethereal gases, caloric, oxygen, and the medium of electricity, are the stimuli by which it is chiefly excited to action; and, by their combination, contribute in some degree to the matter of the system itself; but of the mysterious power that developes the organs and applies the stimuli, that harmonizes the action and constitutes the life, we know nothing.
We see clearly, however, that the moving powers are, for the most part, the muscles; and it is a subject of perpetual astonishment to the physiologist to observe the prodigious force which these vital cords are made capable of exerting, and the infinite variety of purposes to which they thus become subservient. And were it not that the whole universe swarms with proofs of intelligence and design-were it not that there exists, to adopt the beautiful words of the poet