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 varie- 

 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 



