1. The physical researches of the last ten years have put the atomistic theory of matter and electricity on a definite and in all probability permanent basis. We know the exact number of molecules in a given mass of any substance whose molecular weight is known to us, and we know the exact charge of a single electron. This permits us to state as the ultimate aim of the physical sciences the visualization of all phenomena in terms of groupings and displacements of ultimate particles, and since there is no discontinuity between the matter constituting the living and non-living world the goal of biology can be expressed in the same way. This idea has more or less consciously prevailed for some time in the explanation of the single processes occurring in the animal body or in the explanation of the functions of the individual organs. Nobody, not even a scientific vitalist, would think of treating the process of digestion, metabolism, production of heat, and electricity or even secretion or muscular contraction in any other than a purely chemical or physicochemical way; nor would anybody think of explaining the functions of the eye or the ear from any other standpoint than that of physics. When the actions of the organism as a whole are concerned, we find a totally different situation. The same physiologists who in the explanation of the individual processes would follow the strictly physicochemical viewpoint and method would consider the reactions of the organism as a whole as the expression of non-physical agencies. Thus Claude Bernard,[1] who in the investigation of the individual life processes was a strict mechanist, declares that the making of a harmonious organism from the egg cannot be explained on a mechanistic basis but only on the assumption of a “directive force.” Bernard assumes, as Bichat and others had done before him, that there are two opposite processes going on in the living organism: (1) the phenomena of vital creation or organizing synthesis; (2) the phenomena of death or organic destruction. It is only the destructive processes which give rise to the physical manifestations by which we judge life, such as respiration and circulation or the activity of glands, and so on. The work of creation takes place unseen by us in the egg when the embryo or organism is formed. This vital creation occurs always according to a definite plan, and in the opinion of Bernard it is impossible to account for this plan on a purely physicochemical basis. [1] Bernard C., _Leçons sur les Phénomènes de la Vie_. Paris, 1885, i., 22-64. There is so to speak a pre-established design of each being and of each organ of such a kind that each phenomenon by itself depends upon the general forces of nature, but when taken in connection with the others it seems directed by some invisible guide on the road it follows and led to the place it occupies....