We hold this point to be very important; for all experience shows that speculation on the abstract nature of things is to the last degree unprofitable. Nothing is so clear in all sciences as that the proper study of mankind is the Laws by which they are governed. Yet we cannot, in any science, proceed without something to give an intelligible expression to our ideas; which something is essentially hypothetical.
If, for example, we speak of light, we can hardly express our ideas without first supposing of light that it is some subtle substance sent off from luminous bodies, or that it consists in undulations; as we adopt the corpuscular or undulatory theory. It would be easy to form a third, somewhat different from either, and which would yet pretend to no more than to give a still more intelligible expression to phenomena.
Now this is, as it appears to us, just what Mr. Abernethy did. He did not speculate on the nature of life for any other reason than to give a more intelligible expression to Mr. Hunter's other views. At that time there was nothing published, showing that Mr. Hunter's ideas of life were what Mr. Abernethy represented them to be; they might have been remembered by men of his own age, but this was not very good for controversy; and as that was made a point of attack[35], it is well that the since collected "Life and Lectures of John Hunter," by Mr. Palmer, have given us a written authority for the accuracy of Abernethy's representations.
In theorizing on the cause of the phenomena of living bodies, men have, at different times, arrived at various opinions; but although not so understood, it seems to us that they all merge into two—the one which supposes Life to be the result of organization, or the arrangement of matter; the other, that the organization given, Life is something superadded to it; just as electricity or magnetism to the bodies with which these forces may be connected. The latter was the opinion which Mr. Abernethy advocated as that held by Mr. Hunter, and which he honestly entertained as most intelligibly and rationally, in his view, explaining the phenomena.
That such were really the views held by Mr. Hunter, a few passages from the work, as published by Mr. Palmer, will show. "Animal and vegetable substances," says Mr. Hunter, "differ from common matter in having a power superadded totally different from any other known property of matter; out of which various new properties arise[36]." So much for a general view. Next, a reference to particular powers: "Actions in animal bodies have been so much considered under a chemical and mechanical philosophy, that physiologists have entirely lost sight of Life;" again showing how correctly Abernethy had interpreted Hunter's notion of the necessary "Key," as Abernethy phrased it, to his views; Hunter says: "For unless we consider Life as the immediate cause of attraction occurring in animals and vegetables, we can have no just conception of animal and vegetable matter[37]." Mr. Hunter, in relation to the idea of life being the result of organization, shows how faithful an exposition Abernethy had given of his views. "It appears," says he, "that the Living Principle cannot arise from the peculiar modification of matter, because the same modification exists where this principle is no more."—Vol. i, p. 221. And in the same page: "Life, then, appears to be something superadded to this peculiar modification of matter."
Then as to one of the illustrations employed by Abernethy, Hunter, after saying that he is aware that it is difficult to conceive this superaddition, adds: "But to show that matter may take on new properties without being altered itself as to the species of matter, it may not be improper to illustrate this. Perhaps magnetism affords the best illustration. A bar of iron, without magnetism, may be considered as animal matter without life. With magnetism, it acquires new properties of attraction and repulsion," &c.
Mr. Abernethy, as we have said, advocated similar views; and, we repeat, founded his reason for so doing on what he conceived to be the necessity of explaining Mr. Hunter's ideas of life, before he could render his (Hunter's) explanation of the various phenomena intelligible. In all of this, he certainly was expressing Mr. Hunter's own views, with that talent for ornamenting and illustrating everything he discussed, for which he was so remarkable.
Abernethy multiplied the illustrations by showing the various analogies which seemed to him to be presented in the velocity, the chemical, and other powers of Life and Electricity; and, with especial reference to the extraordinary discoveries of Sir Humphrey Davy, added such illustrations, as more recent achievements in chemical science had placed within his grasp; and thence concluding it as evident that some subtile, mobile, invisible substance seemed to pervade all nature, so it was not unreasonable to suppose that some similar substance or power pervaded animal bodies. He guarded himself, however, both in his first and again in his second Course of Lectures, from being supposed to identify Life with electricity, in a long paragraph especially devoted to that object. In his second Course, in 1815, he proceeded to enumerate John Hunter's various labours and contributions to science, as shown by the Museum; imparting great interest to every subject, and in so popular a form, that we wonder now, when (as we rejoice to see) there are some small beginnings of a popularization of physiology, that there is not a cheap reprint of these Lectures.
Keeping, then, his object in view, we cannot see how, as a faithful interpreter of John Hunter, Abernethy could have done less; and if any theory of life at all is to be adopted, as necessary to give an intelligible impression to phenomena, one can hardly quarrel with that which takes the phenomena of life on one hand, and those of death on the other, as the means of expressing our ideas. When we see a man dead, whom we had contemplated alive, it certainly seems that something has left him; and whether we say "something superadded,"—the "breath" or "Life," or by whatever term we call it,—we appear really to express in as simple a form as possible the facts before us. It seems to us that, after all, John Hunter did little more; for the illustration or similitude by which we endeavour to render an idea clear, has in strictness nothing necessarily to do with the idea itself; any more than an analogy, however real the likeness, or a parallelism, however close, represents identity.