192 , BIOLOGY. [Bookii. 



described. It transforms the fecula into dextrine and glycose : 

 it emulsionises the fat matters ; it metamorphoses isomerically 

 the prote'ic substances. But its digestive action diminishes 

 and gradually ceases in the last portion of the intestine, the 

 large intestine. ISTevei-theless the lymphatic vessels of this 

 regioa are stUl charged with chyle exactly like those of the 

 small intestine. 



The origin of the large intestine is distinguished by a dilata- 

 tion called caecum, where the chymic mass sojourns for a longer or 

 shorter period. This caecal cavity acquires considerable dimen- 

 sions in the herbivorous animals, and this is conformable to the 

 general law according to which the digestive system must be so 

 much the more complex the less assimilable are the aliments. 

 Now nothing is less assimilable than the vegetal cellulose, which 

 traverses in great part the digestive tube without being modified, 

 not only in man but even in the herbivorous animals. 



We have now indicated in large outline the diverse digestive 

 processes, the principal metamorphoses which the alimentary sub- 

 tances undergo to become absorbable and assimilable, to become 

 nutriments after being simple aliments. We must next occupy 

 ourselves with the second preparatory phase of nutrition, see by 

 what series of anatomical and physiological processes the assimil- 

 able matters elaborated by digestion are brought into intimate 

 contact with the tissues, with the histological elements, that is to 

 say, give a general description of the circulation. 



