CHAPTER XI. 



OF ALIMENTATION IN GENERAL. 



Whether animals absorb the complex organic substances, 

 in their cruder state, after simple isomeric modifications, whether, 

 in final analysis, they resolve them into their ultimate elements, 

 certain it is that the most complex substances are at the same 

 time the most easy to assimilate, and also those which have the 

 greatest alible value. 



The most important constituent principles of the animal ana- 

 tomical elements are chemically formed by azotized quaternary 

 compounds, and it is indispensable that analogous principles 

 should be found in a considerable quantity in their aliments ; 

 now we know that these quaternary substances are relatively 

 weak in vegetals, that, moreover, they are therein combined with 

 mineral substances. It is then from the animal kingdom itself 

 that animals must especially derive their nourishment. " Eat 

 each other " is for them one of the most imperious nutritive 

 rules. Nevertheless, some of them are herbivorous, but then 

 they must, like the ruminants, have a complex, differentiated 

 digestive tube, a perfected nutritive alembic. 



Most of the lower animals, whose rudimentary digestive tube 

 we have briefly described, are limited almost exclusively to 

 animal nourishment. Many of" them, moreover, are marine 

 animals, that is to say, living in the midst of a vast organic 

 dilution, full of detritus, dissolved, diluted, or fragmentised. 

 Those among them which, are fixed, the polypi, the cirrhopods, 



