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as in years, is but an infant, seems to require not less than a thousand years to give it full vigour and maturity. Extending its enormous arms over the dry and barren soil from which it shoots naturally, it affords shelter to whole nations of barbarians, and in its pleasant subacid fruit administers an ample supply to their hunger.

Let it not, however, be imagined that, by pointing out such frequent instances of resemblance between animal and vegetable life, I mean to degrade the rank of animal being from its proper level; for it will be one of the chief objects of our subsequent studies to develope and delineate its multiform and characteristic superiorities. I am only tracing at present the common principle of vitality to its first outlines: I am endeavouring to unfold to you, in its simplest and rudest operations, that grand, and wonderful, and comprehensive system, which, though under different modifications, unquestionably controlling both plants and animals, from the first moment it begins to act infuses energy into the lifeless clod, draws forth form and beauty, and individual being, from unshapen matter, and stamps with organization and propensities the common dust we tread upon. And if, in this its lowest scale of operation,—if, under the influence of these its simplest laws, and the mere powers (so far as we are able to trace them) of contractility and irritability, it be capable of producing effects thus striking, thus incomprehensible, what may we not expect when the outline is filled up and the system rendered complete 1 What may we not expect when we behold, superadded to the powers of contractility and irritability, those of sensation and voluntary motion? What, more especially, when to these are still fartheradded the ennobling facultiesof a rational and intelligent soul,—the nice organs of articulation and speech,—the eloquence of language,—the means of interchanging ideas, and of imbodying, if I may so express myself, all the phenomena of the mind t

Such are the important subjects to which our subsequent studies are to be directed. In the mean time, from the remarks which have already been hazarded, we cannot, I think, but be struck with the two following sublime characters, which pre-eminently, indeed, distinguish all the works of nature: —a grand comprehensiveness of scheme, a simple but beautiful circle of action, by which every system is made to contribute to the well-being of every system, every part to the harmony and happiness of the whole; and a nice, and delicate, and ever-rising gradation from shapeless matter to form, from form to feeling, from feeling to intellect, from the clod to the crystal, from the crystal to the plant, from the plant to the animal, from brutal life to man. Here, placed on the summit of this stupendous pyramid, lord of all around him, the only being through the whole range of the visible creation endowed with a power of contemplating and appreciating the magnificent scenery by which he is encompassed, and of adoring its Almighty Architect—at once the head, the heart, and the tongue of the whole—well, indeed, may he exult and rejoice! But let him rejoice with modesty. For, in the midst of this proud exaltation, it is possible that he forms but one of the lowest links in "the golden everlasting chain" of intelligence; that he stands on the mere threshold of the world of perception; and that there exists at least as wide a disproportion between the sublimest characters that ever were born of women, our Bacons, Newtons, and Lockes, our Aristotles, Des Cartes, and Eulers, and the humblest ranks of a loftier world, as there is between these highly-gifted mortals and the most unknowing of the animal creation. Yet Hud, thanks to its benificent Bestower! is itself immortal, and knowledge is eternally progressive; and hence man, too, if he improve the talents intrusted to him, as it is his duty to do, may yet hope, unblamed, to ascend hereafter as high above the present sphere of these celestial intelligences, as they are at present placed above the sphere of man. But these are speculations in some degree too sublime for us: the moment we launch into them, that moment we become lost, and find it necessary to return with suitable modesty to our proper province,—an examination of the world around us; where, with all the aids of which we can avail ourselves, we shall still find difficulties enough to try the wisdom of the wisest, and the patience of the most persevering.

LECTURE X.

ON THE PRINCIPLE OF LIFE, IRRITABILITY, AND MUSCULAR POWER.

We have distinguished organic from inorganic matter; and have characterized the former, among other differences, by its being actuated in every separate form by an internal principle, and possessed of parts mutually dependent and contributory to each other's functions. What then is this internal principle,—this wonderful and ever active power, which, in some sort or other, equally pervades animals and vegetables—which extends from man to brutes, from brutes to zoophytes, from zoophytes to fucuses and confervas, the lowest tribes of the vegetable kingdom, whose general laws and phenomena constituted the subject of our last study,—this fleeting and evanescent energy, which, unseen, by the eye, untracked by the understanding, is only known, like its great Author, by its effects; but which, like him too, wherever it winds its career, is perpetually diffusing around it life and health, and harmony and happiness t

I do not here enter into the consideration of a thinking or intelligent principle, or even a principle of sensation, both which are altogether of distinct natures from the present, and to which I shall entreat your attention hereafter; but confine myself entirely to that inferior but energetic power upon which the identity and individuality of the being depend, and upon a failure of which the individual frame ceases, the organs lose their relative connexion, the laws of chemistry, which have hitherto been controlled by its superior authority, assume their action, and the whole system becomes decomposed and resolved into its primary elements.

The subject is, indeed, recondite, but it is deeply interesting: it has occupied the attention of the wisest and the best of mankind in all ages; and though, after the fruitless efforts with which such characters have hitherto pursued it, I have not the vanity to conceive that I shall be able to throw upon it any thing like perfect daylight, you will not, I presume, be displeased with my submitting to you a brief outline of some few of the speculations to which it has given birth, together with the conjectures it has excited in my own mind.

Of the innumerable theories that have been started upon this subject, the three following are those which are chiefly entitled to our attention. Life is the result of a general harmony or consent of action between the different organs of which the vital frame consists.—Life is a principle inherent in the blood.—Life is a gas, or aura, communicated to the system from without. Each of these theories has to boast of a very high degree of antiquity; and each, after having had its day, and spent itself, has successively yielded to its rivals; and in its turn has reappeared, under a different modification, in some subsequent age, and run through a new stage of popularity.

For The System Of Harmony we are indebted to the inventive genius of Aristoxenus, a celebrated physician of Greece, who was at first a pupil of Lamptus of Erythraea, afterward of Xenophylus the Pythagorean, and lastly of Aristotle. He was most excellently skilled in music, and is supposed to have given the name of Harmony to his system from his attachment to this science. It is an ingenious and elegant dogma, and was at one time highly fashionable at Rome as well as at Athens; and is thus alluded to and explained by Lactantius: "As in musical instruments, an accord and assent of sounds, which musicians term Harmony, is produced by the due tone of the strings; so in bodies, the faculty of perception proceeds from a connexion and vigour of the members and organs of the frame."*

To this theory there are two objections, either of which is fatal to it. The

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first is, that admitting the absolute necessity of the health or perfection of every separate part to the health or perfection of the whole, we are still as much in the dark as ever in respect to the principle by which this harmonious machine has been developed, and is kept in perpetual play. The second objection, by which, indeed, it was vigorously attacked by the Epicureans, and at length completely driven from the field, is derived from observing that the health or well-being of the general system does not depend upon that of its collective organs; and that some parts are of far more consequence to it than others. Thus the mind, observes Lucretius, in his able refutation of this hypothesis, may be diseased, while the body remains unaffected; or the body, on the contrary, may lose some of its own organs, while the mind, or even the general health of the body itself, continues perfect.

The abbe Polignac, who, consistently with the Cartesian system, makes a very proper distinction between the principle of the mind or soul, and that of the life, enters readily into the hypothesis of Aristoxenus in regard to the latter power, though he thinks it inapplicable to the former: and Leibnitz appears to have availed himself of it as a means of accounting for the union between the soul and body in his celebrated system, which he seems to have named, from the theory before us, the system of Pre-established Harmony'. By a writer of the present day, however, M. Lusac, the doctrine of Aristoxenus seems to have been resuscitated in its fullest scope, and even to have been carried to a much wider latitude than its inventor had ever intended: for the theory of M. Lusac affects to regard, not only the frame of man and other animals, but the vast frame of the universe, as a sort of musical organ or instrument; the concordant and accumulated action of whose different parts or agents he denominates, like Aristoxenus, harmony. "Concerts of music," says he, "afford a clear example: you perceive harmony in music when different tones, obtained by the touch of various instruments, excite one general sound, a compound of the whole." This observation he applies to the grand operations of nature, the irregularities of which, resulting from inundations, earthquakes, volcanoes, tempests, and similar evils, this philosopher considers as the dissonances occasionally introduced into music to heighten the harmony of the entire system. With respect to the harmony of the human frame, individually contemplated, or the concordant action of the different parts of the body, he observes, "It may be said, that of this principle I have merely a confused notion; and I admit it, if the assertion imply that I have neither a perfect nor a distinct, nor an entire comprehension of what produces this harmony—in what it consists, or how it acts. I know not what produces the harmony of various instruments heard simultaneously; but I can accurately distinguish the sounds which are occasioned when musicians are tuning, from those which are produced when, being completely in tune, and every one uniting in the piece, the separate parts are executed with precision. When I hear an harmonious sound, whatever be its nature, I can distinguish the harmony, though incapable of investigating its cause."*

I shall only observe, farther, that in the doctrine of Mr. (now Sir Humphry) Davy, which holds life itself as a perpetual series of corpuscular changes, and the substrate, or living body, as the being in which these changes take place, we cannot but observe a leaning towards the same system; and we shall have occasion, in a subsequent lecture, to'notice one or two others of equally modern date that touch closely upon it in a few points.f

Let us pass on, then, to a consideration of the second hypothesis I have noticed, and which consists in regarding the Blood lTBKLr As The Principle or Life. This opinion lays claim to a still higher antiquity than the preceding; and, in a general view of the question, is far better founded. It has the fullest support of the Mosaic writings, which expressly appeal to the doctrine, that " the life of all flesh is the blood thereof,"}: as a basis for the culi

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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 irop^tfpcof Mmrot. or purple death, of Homer, and the purptrta 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 isto that accurate and truly original physiologist, Mr. John Hunter, that we canonlj 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 observersucceeded 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 neverarise 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 n°' 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 contracting, like the solid muscular fibre, upon the application of a stimulus; of which every one has an instance in that 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 »»tf7

• 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 Exqcisitelt 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,
Through the whole system's utmost depth dilTus'd,
And lives as soul of e'en the soul itself.t

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.J 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 any nerve.

t Nam penitus prorsum latet h»c natnra. subestque;
Nec magis hac infra qnidquam est in corpora nostra;
Atquc anima est animas proporro totius ipsa.

De Rer. Nat. lit. 774.

t ttemcton sur llrriiabtliie, coaatderee comrae prlndpe ds vis dans la nature organises Paris, 17W

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