996 DIGESTION 



juice. .When the peptone stage has been passed, the biuret reaction is no longer 

 obtained. Regarding the degree of alkalinity existing in the duodenum much 

 uncertainty prevails. While pancreatic juice is a strongly alkaline secretion, 

 owing to its content in sodium carbonate, it must be remembered that the alkalin- 

 ity of this medium must be changed repeatedly by the entrance of the fresh acid 

 chyme. Its reaction may then become neutral, but the action of trypsin cannot 

 be unfavorably affected by a condition of this kind, because most effective artificial 

 media are usually made by dissolving commercial trypsin in only 0.2 to 0.3 per cent, 

 of sodium carbonate. It is true, however, that larger amounts of this enzyme 

 require a larger amount of this salt. It has been pointed out above that the con- 

 version of trypsinogen into trypsin necessitates the presence of enterokinase or cal- 

 cium salts. 1 It is also said that erepsin may be present at times in pancreatic juice, 

 because when inactivated, this secretion may digest casein but not other proteins. 



(b) Amylolytic. Pancreatic juice contains an amylase, known as amylopsin, 

 which hydrolyses the starches more rapidly than ptyalin. Even unboiled starch 

 is affected by it under formation of erythro-dextrin and maltose. In a nearly 

 neutral medium this disaccharide is converted further into the monosaccharide 

 dextrose or glucose. This additional hydrolysis is dependent upon the presence 

 of a second ferment, maltase. 



(c) Lipolytic. 2 The powerful fat-splitting enzyme of pancreatic juice is 

 called steapsin. It changes neutral fats, such as the triglycerides of palmitic, 

 stearic and oleic acids, into the corresponding fatty acids. Since this medium pos- 

 sesses an alkaline reaction, these fatty acids unite with the alkaline bases to form 

 soaps which then appear as films upon the outer surfaces of the fat-globules and 

 prevent them from coalescing. These emulsions assume a more stable character 

 in the presence of proteins, and colloids. 



(d) Milk-curdling. 3 Pancreatic juice also possesses the power of clotting 

 milk, but this action may not be due to the presence of a special enzyme. It differs 

 in its character from that of rennin. 



The Function of Bile. The velocity with which lipolysis takes 

 place in the small intestine, is considerably increased by the presence 

 of bile, the active agent concerned in this process being the bile salts. 

 These act in two ways, namely by their solvent action on fatty acids 

 and soaps and secondly, by their property of diminishing the surface 

 tension between the fat and the water. This enables the intestinal 

 juices to enter into closer relation with .the globules of fat. Con- 

 sequently, the digestive value of bile lies in its adjuvant power of 

 furnishing a more appropriate medium for the interaction between the 

 steapsin and the fatty acids than the pancreatic juice alone could 

 possibly constitute. In some animals, it also contains a weak amyloly- 

 tic enzyme. 



Bile also serves as a vehicle for the fats during their absorption. 

 This statement implies that the end-products of lipolysis traverse 

 the intestinal epithelium not merely in an emulsified form, but as fatty 

 acids or soaps and glycerin. This gives rise to a "circulation of the 

 bile," because some of the biliary substances are again absorbed and 

 made use of later on in the manner just indicated. 



While the bile salts possess mild antiseptic qualities, the bile itself 



1 Schepowalnikow, Dissertation, St. Petersburgh, 1899, and Bayliss and Star- 

 ling, Jour, of Physiol., xxviii, 1902, 375. 



2 Connstein, Ergebn. der Physiol., iii, 1904. 



3 Kiihne Verh., med. Verein, Heidelberg, iii, 1881. 



