228 LIFE AND DEATH. 



kinds, the one destructive and simplifying, the other 

 synthetic, constructive, or assimilating. This totality 

 of reactions constitutes nutrition. Hence the two 

 phases that it is convenient to consider in this func- 

 tion — assimilation and disassimilation. This twofold 

 chemical movement or metabolism corresponding to 

 the two categories of vital phenomena, of destruction 

 (catabolism) and of synthesis (anabolism) is therefore 

 the chemical sign of vitality in all its forms. But it 

 is clear that disassimilation or organic destruction, 

 which is destined to furnish energy to the organism 

 for its different operations, reappears in the plan of 

 the general phenomena of nature. It is not specific- 

 ally vital in its principle. Assimilation, on the other 

 hand, is in this respect much more characteristic. 



To some physiologists nutrition is only assimila- 

 tion. Of the two aspects of metabolism they consider 

 only one, the most typical, Ad-similare, to assimilate, 

 to restore the substance borrowed from the ambient 

 medium, the alimentary substances, similar to living 

 matter, to make living matter of them, to increase 

 active protoplasm — this is indeed the most striking 

 phenomenon of vitality. To grow, to increase, to 

 expand, to invade, is the law of living matter. 

 Assimilation, nutrition in its essentials, is, according 

 to the definition of Ch. Robin, "the production by the 

 living being of a substance identical with its own." 

 It is the act by which the living matter, the proto- 

 plasm of a given being, is created. 



Permanence in Nutrition. — Nutrition presents one 

 quite remarkable character — permanence. It is a vital 

 manifestation, a property if we look at it in the cell, 

 in the living substance, a function if we consider it in 

 the animal or in the plant as a whole, which is never 



