188 BIOLOGY. [Book ii. 



points were produced first of all sanguineous stages, thereupon a 

 softening of the naucous membrane, which then became incap- 

 able of resisting the action of the gastric juice, and was digested, 

 whence ulcerations and even perforations of the stomach. 



Certain general states influence, moreover, the peptic secretion ; 

 for example, according to the observations of M. SchifE, fever com- 

 pletely abolishes this secretion. The stomach is then absolutely 

 incapable of digesting ; it absorbs, but it requires aliments 

 directly assimilable, such as dextrine glycose, the artificial 

 peptones of Oorvisart.^ 



C. Intestinal Digestion. — 'Tntestinal digestion exists really, that 

 is to say, with its distinctive characteristics, there only where 

 exist also its true agents, that is to say, the hepatic and pancreatic 

 glands. We have seen that the secretory elements of the bile 

 seem to be at first in the echinoids, simple epithelial cells Hning 

 the internal surface of the intestine. The epithelial hepatic cells 

 are, definitively, everywhere and always the creators of bile in 

 the whole of the animal kingdom ; but in proportion as we rise in 

 the zoological series we see these cells becoming more and more 

 numerous, and accumulating in special apparatus more and more 

 complex. They are first of all simple csecums, in the heart of 

 which the cells have birth, fill themselves with bile, which they 

 afterwards allow to escape, by dissolving, or, as in the insects, 

 there are tubes in which urine and bile are generated side by 

 side. 



In the arthropods there exists a voluminous liver, especially 

 in the ci'ustaceans and the insects. The moUusks are also pro- 

 vided with a voluminous liver, dividing into lobes, fabricating at 

 the same time sugar and bile like that of the superior vertebrates. 



In these last the bile is secreted abundantly, sojourns in part 

 at least in a special pouch called biliary vesicle, and is finally 

 poured into the first part of the small intestine, the duodenum. 

 The bile is, as every one knows, .a yellowish or greenish liquid, 

 bitter, holding in solution a colouring matter, the biliverdine, 

 1 M. Schiff, loo. cii., p. 269. 



