CHAPTER IX. 



OF THE MEANS OF ANIMAL NUTRITIOBT. 



Every organised being is tlie seat of an incessant and double 

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

 double movement may be accomplisbed, and tbis is tbe fundst- 

 mental condition of life, it is necessary tbat it sbould be 

 constantly alimented by substances so composed, tliat tbey can 

 be incorporated in tbe organism. 



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

 animals, tbe work is relatively simple, since tbey draw food 

 direct, and witbout preparation from the ambient medium. In 

 tbe superior animals, tbe phenomena are complicated. Before us 

 are tben brought very diversified organisms, where tbe 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 tbe alimen- 

 tary substances, once modified and transformed into nutriments, 

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

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

 if tbe residua unfit to sustain the vital movement were noi 



