[197] Other definitions refer the idea of Life to the idea of Organization. ‘Life is the activity of matter according to laws of organization[65].’ We are then naturally led to ask, What is Organization? In reply to this is given us the Kantian definition of Organization, which I have already quoted elsewhere[66], ‘An organized product of nature is that in which all the parts are mutually ends and means[67].’ That this definition involves exact fundamental ideas, and is capable of being made the basis of sound knowledge, I shall hereafter endeavour to show. But I may observe that such a definition leads us somewhat further. If the parts of organized bodies are known to be means to certain ends, this must be known because they fulfil these ends, and produce certain effects by the operation of a certain cause or causes. The question then recurs, what is the cause which produces such effects as take place in organized or living bodies? and this is identical with the problem of which in the last chapter we traced the history, and related the failure of physiologists in all attempts at its solution.
[65] Schmid, Physiologie, b. ii. p. 274.
[66] Hist. Ind. Sc. b. xvii. c. viii. s. 2.
[67] Kant, Urtheilskraft, p. 296.
4. But what has been just said suggests to us that it may be an improvement to put our problem in another shape:—not to take for granted that the cause of all vital processes is one, but to suppose that there may be several separate causes at work in a living body. If this be so, life is no longer one kind of activity, but several. We have a number of operations which are somehow bound together, and life is the totality of all these: in short, life is not one Function, but a System of Functions.
5. We are thus brought very near to the celebrated definition of life given by Bichat[68]: ‘Life is the sum of the functions by which death is resisted.’ But upon the definition thus stated, we may venture to observe;—first, that the introduction of the notion of [198] death in order to define the notion of life appears to be unphilosophical. We may more naturally define death with reference to life, as the cessation of life; or at least we may consider life and death as correlative and interdependent notions. Again, the word ‘sum,’ used in the way in which it here occurs, appears to be likely to convey an erroneous conception, as if the functions here spoken of were simply added to each other, and connected by co-existence. It is plain that our idea of life involves more than this: the functions are all clearly connected, and mutually depend on each other; nutrition, circulation, locomotion, reproduction,—each has its influence upon all the others. These functions not merely co-exist, but exist with many mutual relations and connexions; they are continued so as to form, not merely a sum, but a system. And thus we are led to modify Bichat’s definition, and to say that Life is the system of vital functions.
[68] Physiological Researches on Life and Death.
6. But it will be objected that by such a definition we explain nothing: the notion of vital functions, it may be said, involves the idea of life, and thus brings us round again to our starting-point. Or if not, at least it is as necessary to define Vital Functions as to define Life itself, so that we have made little progress in our task.
To this we reply, that if any one seeks, upon such subjects, some ultimate and independent definition from which he can, by mere reasoning, deduce a series of conclusions, he seeks that which cannot be found. In the Inductive Sciences, a Definition does not form the basis of reasoning, but points out the course of investigation. The definition must include words; and the meaning of these words must be sought in the progress and results of observations, as I have elsewhere said[69]. ‘The meaning of words is to be sought in the progress of thought; the history of science is our dictionary; the steps of scientific induction are our definitions.’ It will appear, I think, that it is more easy for us to form an idea of a separate Function of the [199] animal frame, as Nutrition or Reproduction, than to comprehend Life in general under any single idea. And when we say that Life is a system of Vital Functions, we are of course directed to study these functions separately, and (as in all other subjects of scientific research) to endeavour to form of them such clear and definite ideas as may enable us to discover their laws.
[69] Hist. Ind. Sc. b. xiii. c. ix.