DIGESTION AND RESORPTION 87 



the horse, this empties directly into the duodenum a short 

 distance from the stomach. In cattle, sheep and swine, the 

 bile is stored up in the gall bladder, a reservoir from which a 

 duct leads to the duodenum. 



The chief action of the bile is upon fats of the feed. To a 

 small extent, it saponifies them and it also assists in emulsifying 

 them. Its digestive action may, however, be more conveniently 

 considered along with that of the pancreatic juice (126, 135). 

 In addition to its action upon the fats, an antiseptic effect and 

 also a stimulating effect upon peristalsis have been ascribed to 

 the bile. 



125. The intestinal juice. In addition to the external 

 glands (pancreas and liver), already mentioned, the walls of 

 the small intestine contain a large number of small glands of 

 two kinds, Brunner's and Lieberkiihn's glands, which yield an 

 intestinal juice containing a number of enzyms. Prominent 

 among these are the invertases maltase, sucrase and lactase, 

 which act upon the corresponding disaccharids, the maltose re- 

 sulting from the digestion of starch being converted into dextrose, 

 sucrose into a mixture of dextrose and levulose, and lactose, in 

 suckling animals at least, into dextrose and galactose. 



There may also be extracted from the mucous membrane of 

 the small intestine a protease called erepsin. This enzym does 

 not act upon the native proteins, with the exception of casein, 

 but acts powerfully upon the derived proteins (proteoses and 

 peptones), hydrolyzing them and breaking them down very 

 completely to their constituent amino acids. The presence of 

 erepsin has also been demonstrated in the intestinal juice, but its 

 action in this case was weaker than in the extracts of the intesti- 

 nal wall and it may be that a portion of its action in the living 

 animal takes place within the cells in which it is produced. 



The presence in the intestinal juice of an amylase, a lipase 

 and of ferments (nucleinases and nucleotidases) , which act upon 

 the nucleic acids has also been demonstrated. 



126. Intestinal digestion. In the duodenum the neutraliza- 

 tion of the acid material coming from the stomach is effected 

 by the alkalies of the bile and pancreatic juice, while the bile 

 also precipitates proteins and partly digested proteins in com- 

 bination with the bile acids and this precipitate carries down 

 with it mechanically the pepsin which is present. In these 



