ANIMAL GRAFTS AND REGENERATIONS. 249 
haying at bottom the same forces, the same tendercies, the 
same aspirations as-the more or less complex systems to 
which it gives birth by a thousand associations and vari- 
ous interweavings. ‘ Nature’s machines,” says Leibnitz, 
“ are machines throughout, however small the part in them 
one may take; or, rather, the least part is in its turn an infi- 
-nite world, and one even that expresses, after its fashion, all 
that there is in the rest of the universe. This surpasses 
our conception, yet we know that it must be so, and all 
that infinitely infinite variety is established in all its parts 
by a sublime constructive wisdom more than infinite.” ’ 
But what is in itself the vital force peculiar to these tiny 
machines, the force that we observe maintaining itself in 
the several parts of the organism, and restoring the voids 
produced in the tissues ? what is the fundamental character, 
the mark of life ? _ It is nutrition, that is to say, the fact, as 
plain as it is inexplicable, of the continuous molecular re- 
_ newal of organized substance. It is in the understanding 
of the phenomena of nutrition, the “ trophic ”’ phenomena, 
that the whole future of biology lies. Weshall never grasp 
the secret of the deepest and most essential vital actions, 
until we shall comprehend the equations of the statics and 
dynamics of those fleeting systems, restlessly passing 
through cycles of change, which compose the anatomical 
elements. 
Whatever future the knowledge of trophic phenomena 
will bring with it, the conception of life won for us by nat- 
ural philosophy opens from this time forward a new path 
for investigations. It suggests the thought of examining 
into the variations of physiological determinism, that is, of 
studying the boundaries within which life moves, or, in other 
words, the profound modifications of which organisms are 
susceptible, whether from the point of view of the specific 
1 “etter to Bossuet,” Unedited Works, published by Foucher de 
Careil, vol. i., p. 276. 
