outside of the being, but which are in their turn destroyed and pass into other conditions unsuitable to life, and in which they are cast out to re-enter the inorganic world, which is enriched through them with ammonia, carbonic acid, and oxygen. We are not acquainted with the nature of this movement; we know only that it exists by comparing what goes in and what goes out, and these with the intermediate term, the living substance itself. We know that it is propagated at the same time in all the tissues and all the organs of the being, offering in each a special modality while retaining always the same fundamental character.
This movement is fundamental to the tissues of the living being, from the most simple of them, like the substance of the bone, to the most complex, like that of the muscles or the brain. It is always in the living being, whether it is growing, thriving, or declining toward death, or is attainted with different passional, morbid conditions that might affect it. It is always present in the infinite variety of physiological acts of which our life is made up and which all inevitably lead to an impending molecular modification: the sensation of the retina disturbed by a light-ray, the contraction of a muscle, and even thought. In connection with the last, the effort has been made to reach by tortuous ways the nature of the chemical reactions that necessarily accompany all brain work. Whether this is reached or not, it is impossible to conceive the operation of the nervous elements otherwise than as a phenomenon of nutrition—that is, as a modification brought about in the molecular movement.
But we are still unable to penetrate and discover the true nature of that inner molecular movement which makes of animated bodies a world apart from the great cosmos. What are the origin and nature of that new energy communicated to inert matter, giving it properties or rather faculties which it had not before, and which are additional to all those with which the chemist and physicist are acquainted? Let us say, further, that they are added to these without contradicting them, as was believed for a long time when a kind of antagonism was supposed between life and the physico-chemical forces. Life is in no way a triumph over these forces, and they always keep their predominance.
Vital movement is, after all, only an episodical modality of the universal faculty which simple and compound chemical bodies have of reacting upon one another. It requires for its manifestation, like every other reaction, definite conditions, confined within narrow limits, of pressure, temperature, and light.
But the thing we are absolutely ignorant of is the real nature of those inner reactions of which we can not in many cases give the rigorous formula and still less define the thermic equivalent; the generic quality, as it were, of those movements, at once special
