Lotze in his oft-quoted article, “Leben, Lebenskraft” (Life, Vital Force), in Wagner's “Hand-Wörterbuch der Physiologie,” 1842, gave the signal for this reaction. The change, however, did not take place suddenly. The most important investigators in their special domain, the physiologist Johannes Müller, the chemist Julius Liebig, remained faithful to a modified vitalistic standpoint. But in the following generation the revolution was complete and energetic. With Du Bois-Reymond, Virchow, Haeckel, the anti-vitalistic trend became more definite and more widespread. It had a powerful ally in the Darwinian theory, which had been promulgated meanwhile, and at the same time in the increasingly materialistic tendency of thought, which afforded support to the mechanical system and also sought foundations in it.
The naturalistic, “mechanical” interpretation of life was so much in the tenor of Darwin's doctrine that it would have arisen out of it if it had not existed before. It is so generally regarded as a self-evident and necessary [pg 192] corollary of the strictly Darwinian doctrine, that it is often included with it under the name of Darwinism, although Darwin personally did not devote any attention to the problem of the mechanical interpretation of life. Any estimate of the value of one must be associated with an estimate of the other also.
It goes without saying that the theory of life is dependent upon, and in a large measure consists of physico-chemical interpretations, investigations, and methods. For ever since the attention of investigators was directed to the problems of growth, of nutrition, of development and so on, and particularly as knowledge has passed from primitive and unmethodical forms to real science, it has been taken as a matter of course that chemical and physical processes play a large part in life, and indeed that everything demonstrable, visible, or analysable, does come about “naturally,” as it is said. And from the vitalistic standpoint it has to be asked whether detailed biological investigation and analysis can ever accomplish more than the observation and tracing out of these chemical and physical processes. Anything beyond this will probably be only the defining and formulating of the limits of its own proper sphere of inquiry, and a recognition, though no knowledge, of what lies beyond and of the co-operative factors. The difference between vitalism and the mechanical theory of life is not, that the one regards the processes in the organism as opposed to those in the inorganic world while the other identifies them, but that vitalism regards [pg 193] life as a combination of chemical and physical processes, with the co-operation and under the regulation of other principles, while the mechanical theory leaves these other principles out.
Notwithstanding the many noteworthy reactions, we are bound to regard the present state of the theory of life as on the whole mechanical. The majority of experts—not to speak of the popular materialists, and especially those who, sailing under the flag of materialistic interpretation, have their ships full of vitalistic contraband—regard as the ideal of their science an ultimate analysis of the phenomena of life into mechanical processes, into “mechanics of the atom.” They believe in this ideal, and without concealing that it is still very far off, do not doubt its ultimate attainability, and regard vitalistic assumptions as obstacles to the progress of investigation. Moreover, this aspect of the problem seems likely enough to be permanent with the majority, or, at any rate, with many naturalists, though it is obviously one-sided. For it has always been the task of this line of investigation to extend the sphere within which physical and chemical laws can be validly applied in interpreting vital processes, and the results reached along this line will always be so numerous and important that even on psychological grounds the mechanical point of view has the best chance for the future. Furthermore, the maxim that all the phenomena of nature must be explained by means of the simplest factors and according to the smallest possible [pg 194] number of laws, is usually regarded as one of the most legitimate maxims of science in general, so that the resolute pertinacity with which many investigators maintain the entire sufficiency of the mechanical interpretation, far from being condemned as materialistic fanaticism, must be respected as the expression of scientific conscience. Even when confidence in the one-sided mechanical interpretation of vital processes sometimes fails in face of the great and striking riddles of life, it is to be expected that it will revive again with each new success, great or small.[58]
The mechanical conception of life which now prevails is made up of the following characteristics and component elements. These also indicate the lines along which the arguments are worked out—lines which glimmered faintly through the mechanical theories of ancient times, but which have now been definitely formulated and supported by evidence.
The Conservation of Matter and Energy.
1. The whole mechanical theory is based upon a law which is not strictly biological but belongs to science in [pg 195] general—the law of the conservation of matter and energy. This was first recognised by Kant as a general rational concept in his “Critique” and in the “Grundlegung der Metaphysik der Naturwissenschaft,” and was transferred by Robert Mayer and Helmholtz[59] to the domain of natural science. Just as no particle of matter can come from nothing or become nothing, so no quantum of energy can come from nothing or become nothing. It must come from somewhere and must remain somewhere. The form of energy is continually changing, but the sum of energy in the universe remains invariable and constant. Therefore, it seems to follow, there can be no specific vital phenomena. The energies concerned in the up-building, growth, and decay of the organism, and the sum of the functions performed by it, must be the exact resultant and equivalent of the potential energies stored in its material substance and the co-operative energies of its environment. The particular course of transformations they follow must have its sufficient reason in the configuration of the parts of the organism, in its relations to the environment, and the like. An intervention of “vitalistic” principles, directions and so forth, would, we are told, involve a sudden obtrusion and disappearance again of energy-effects which had no efficient cause in the previous phenomena. From any point of view it would be a miracle, and in particular it would [pg 196] be doing violence to the law of the constancy of the sum of energy.
Apart from the inherent general “instinct”—sit venia verbo, for no more definite word is available—which is the quiet Socius, the concealed but powerful spring of the mechanistic convictions, as of most others, this law of the conservation of energy is probably the really central argument, and it meets us again more or less disguised in what follows.