CHAPTER IX. 



OF THE MEANS OF ANIMAL NUTRITION. 



EVERY organised being is the seat of an incessant and double 

 movement of assimilation and dis-assimilation. In order that this 

 double movement may be accomplished, and this is the funda- 

 mental condition of life, it is necessary that it should be 

 constantly alimented by substances so composed, that they can 

 be incorporated in the organism. 



In almost all vegetals, and in a certain number of the lower 

 animals, the work is relatively simple, since they draw food 

 direct, and without preparation from the ambient medium. In 

 the superior animals, the phenomena are complicated. Before us 

 are then brought very diversified organisms, where the division 

 of physiological labour is pushed farther and farther. But in- 

 this case, the anatomical elements seem to have lost, in vegetative 

 energy what they have gained in fineness. In order to live, they 

 need to absorb highly elaborated organic substances, and, for 

 this purpose, the organism is furnished with a special apparatus, 

 whose office consists in forming a kind of physiological kitchen, 

 to modify the elements, to accomplish the first chemical trans- 

 formation, which renders them more suitable for assimilation. 

 This apparatus is the digestive system. 



But this chemical elaboration would be useless if the alimen- 

 tary substances, once modified and transformed into nutriments, 

 did not come in contact with all the anatomical elements, super- 

 ficial or hidden, in the suitable physical and chemical conditions, 

 if the residua unfit to sustain the vital movement were not 



