ANIMAL GRAFTS AND REGENERATIONS. 253 
might not undertake to modify directly the existing com- 
position of anatomical elements. 
This latter conception, which sets the bounds of physi- 
ological determinism at a far greater distance than the 
former does, is also capable of verification by experiments. 
Just as we act upon phenomena of evolution, we may, by 
processes of methodical and persistent boldness, disturb 
the order of the operations of nutrition. The method we 
have followed in our own researches on this subject con- 
sists in suppressing certain essential principles of nutrition, 
and substituting for them new immediate principles, more 
or less similar. But the immediate principles that are nu- 
tritious are found mingled with the substances of food in 
the conditions most favorable to assimilation. The mineral 
salts in them are intimately combined with azote matters. 
In order, then, to replace these mineral salts of common 
food with others, phosphate of lime, for instance, with phos- 
phates of a different kind, it is necessary not merely to dis- 
engage the food as much as possible from the salts that we 
wish to reject, but also to associate with it in the closest 
manner the new salts which we intend to fix in the system ; 
that is to say, we must introduce them into it under the 
form fittest for assimilation, and most capable of overcom 
ing the natural resistance of the organism. It is also clear 
that it is best to experiment on young animals, in which 
the action of assimilation is most intense. Under such . 
conditions, and by such processes, we reach the end of 
modifying the order and kind of the immediate principles 
in organized substance, Personal experiments permit us 
at least to assert this, as far as it regards the bony tissue, 
and thus far we have seen nothing that compels us to doubt 
our power of producing at length, by gradual transforma- 
tions, following upon certain contrivances of nutrition, or- 
ganisms of a new and harmonious equilibrium, from the 
point of view of the system of immediate principles. In 
