DIGESTION IN THE SMALL INTESTINE 395 



the end, points to the fact that it is a secretion which plays an impor- 

 tant part in the digestive processes. Bile is not an actual digesting 

 agent, for by itself it has little or no digestive power. It is true in 

 some cases it contains an amylopsin, but the action of this enzyme 

 is negligible. Bile plays an important part in the preparatory digestive 

 and absorptive processes of the small intestine. As its early presence 

 in the duodenum would suggest, bile is essentially " the preparer for 

 digestion." The functions of the bile may be summarized as follows: 



1. The rancid fats in the chyme are far more efficiently emulsified 

 in the presence of bile than in the presence of the alkaline juices alone. 



2. The undigested proteins and proteoses are precipitated by the 

 bile from their acid solution, and thus delayed in the digestive 

 area of the duodenum ; if they remained in solution, they might be 

 passed on too quickly ; in this state, too, they are more easily assailable 

 by the digesting enzymes, since food in a particulate form is more 

 easily attacked. 



3. The digestive processes are helped (1) by the neutralization 

 of the acid in the chyme; (2) by activation of tne lipolytic (fat- 

 splitting) enzymes of the pancreatic juice; (3) by all the digestive 

 enzymes working with greater rapidity in the presence of bile. 



4. In the absorptive processes, bile is especially helpful in 

 promoting the absorption of fat. When bile is withheld from the 

 intestine, much of the fat eaten escapes digestion and absorption, and 

 appears in the faeces. Bile aids this absorption by dissolving fatty 

 acids and taking into solution insoluble soaps of calcium and magne- 

 sium formed in the course of digestion. 



5. By its property of lowering surface tension, bile enables the 

 substances to be absorbed to come into more intimate contact with 

 the absorbing surface. 



6." Bile has been credited with antiseptic properties. There is 

 nothing in support of this view; in fact, special media for the growth of 

 bacteria are sometimes prepared containing it. The truth of the matter 

 is this: Owing to the presence of bile, all digestive, and therefore 

 absorptive, processes are quickened, so that the bacteria of the intestine 

 have little chance to carry putrefactive and fermentative processes 

 beyond normal limits. It is the digestion and absorption of fats 

 which is of particular importance, for, when fats are not well digested, 

 protein digestion is hindered by their presence, and putrefactive changes 

 then take place. 



7. The chief excretory function of the bile would seem to be to 

 rid the organism of the dissolved cholesterin, some of the cholalic 

 acid, and the bile pigment. 



THE PANCREAS AND ITS SECRETION. The pancreas is a long, 

 narrow gland of the acino-tubular type. In man, its main duct (the 

 duct of Wirsung) opens into the duodenum, together with the common 

 bile duct, about 8 to 10 centimetres beyond the pyloric orifice. The 

 point and mode of entry, however, varies in other animals. In the 

 dog, there are two ducts the one opening with the bile duct, the 

 other 3 to 5 centimetres lower down. The latter is usually the 



