252 NATURE AND LIFE. 
the same composition in all living species, at the lowest 
degrees as well as at the heights of the zoological scale; 
that is to say, that living molecules, whatever be the yarie- 
ty of the different systems they form by association, are 
at bottom always the same. On what do this unity and 
constancy of composition in the elements out of which or- 
ganic tissues are woven, depend? On the fact that they 
all live in the same medium, and all positively absorb ex- 
actly the same nutritive materials. We might believe 
that the organization exerts an act of choice among the 
mass of the bodies that surround it, that it has a particular 
affinity for certain principles, and a repugnance to assimilat- 
ing others. Very certainly, some substances, a very small 
number of them, are absolutely incompatible with life, at 
least such as we conceive it; but this does not prove that 
organisms are endowed with the power to exert distinct 
selection among the total chemical ingredients of the air, 
earth, and water. The first germs, and the animals born 
of them, took naturally and spontaneously what they found 
around them, and grew by degrees accustomed to it. The 
clay out of which a mysterious hand has fashioned them is 
a complicated combination of every thing that exists in the 
medium in which they float. That which was chance in 
their original constitution became the law of their ultimate 
constitution. Those immediate principles, thus more or less 
readily assimilated during the rudimentary periods, became 
adapted, under the sway of heredity, to conditions most 
favorable to life; harmony gradually arose between matter 
and form; and the nature of the functions followed upon 
that of the organs: At least nothing authorizes us to as- 
sert the contrary, and every thing leads to the belief that, 
if the materials of the earthly medium had been otherwise 
proportioned, the composition of living organs would not 
be the same that we know. We thus see that the ques- 
tion is no other than a completely rational one, whether we 
Mba 
