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, further, that in the doctrine of 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.+

Let us pass on, then, to a consideration of the second hypothesis I have noticed, and which consists in regarding the BLOOD ITSELF AS THE PRINCIPLE OF 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

* Du Droit Naturel, Civil, et Politique, tom. i. 154.

Vol. II. Series III.

Lect. v. + Levit. xvii. 14.

culinary 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, Hindus, 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 πορφύρεος θάνατος, or purple death of Homer, and the purpurea anima, or purple life of Virgil, (phrases evidently derived from this theory,) are common-place terms amidst 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 alone 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 mean 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 mean 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

* Hunter on the Blood, p. 20.

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 phænomenon, 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 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

*

* Dr. Munro has proved, that the limb of a frog can live and be nourished, and its wounds heal, without any nerve.

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 thus 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 come immediately 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.

SITELY SUBTLE GAS or AURA

The next theory, therefore, to which I have adverted, undertakes to explain in what this foreign and superadded principle consists. SOME EXQUI- 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 time 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: