CHAPTER YL 



OF DIS-ASSIMILATION AMONGST ANIMALS. 



When once the nutriments are elaborated and assimilated, the 

 first half of the nutritive movement is accomplished ; but in 

 the living substance there is never any repose, and these same 

 materials, employed so far in a work of reparation, of recon- 

 struction, are in their turn worn out ; in their turn they become 

 unfit to figure in a living tissue, and are eliminated under various 

 fcH-ms. 



The substances expulsed from the animal mechanism, the 

 elements of regression, may be divided into three great categories ; 

 (1), mineral substances; (2), mixed substances, altogether mineral, 

 in their properties, but not formed spontaneously apart from 

 animal organisms ; (3), finally, complex, azotized, but crystallizablo 

 compounds. No truly proteic substances are met with. These 

 last are not noi-mally expulsed from the animal organisms. 



The mineral substances are either gaseous, or liqtdd, or solids 

 in solution. The gases in almost all animals are azote, oxygen, 

 and carbonic acid. A small part of the azote is produced by the 

 complete combustion of a portion of the azotized substances ; 

 the larger part is simply aerian azote which, after having 

 penetrated the tissues, is expulsed from them without having 

 fulfilled any appreciable function. But the experiments of M. 

 Eegnault have shown that animals, even when in a state 

 of complete repose, and particularly when they have a richly 

 azotized diet, exhale a small proportion of azote, the residuum 



