DIGESTIVE CHANGES IN THE SMALL INTESTINE 345 



of secretion, the succus entericus, can be obtained by this means. Intestinal 

 juice is a yellowish alkaline fluid with a specific gravity of ion and con- 

 tains about 2.5 per cent of solid matters. 



Intestinal juice has only slight digestive action. It contains a weak pro- 

 teolytic enzyme and a weak amylolytic enzyme. Maltase is also present. But 

 the chief and most profound importance is given to the intestinal juice by the 

 discovery of the activating enzyme, enterokinase. This specific activating 

 enzyme for the trypsinogen of the pancreatic juice places the intestinal secre- 

 tion in the rank of necessary secretion for efficient digestion. Enterokinase 

 can be prepared by extracting the superficial scrapings of the intestinal mucous 

 coat. The duodenal region is richest in enterokinase, but the secretion of the 

 lower intestinal lengths also contains the enzyme. 



Extracts of the mucosa of the intestine have been found to contain another 

 substance which has the specific action of splitting peptones into simpler 

 amino bodies. This substance has been called erepsin. 



There are, therefore, three important new substances in the succus en- 

 tericus (or in the extract of the glands), secretin, erepsin, and enter -okinase, 

 in addition to the proteolytic and diastatic enzymes. 



Summary of the Digestive Changes in the Small Intestine. The 

 thin chyme which, during the whole period of gastric digestion, is being con- 

 stantly squeezed or strained through the pyloric orifice into the duodenum, 

 consists of albuminous matter that is broken down, dissolving and half dis- 

 solved; of fatty matter broken down and melted, but not dissolved at all; 

 of starch in various stages of the process of conversion into sugar, and as 

 it becomes sugar dissolving in the fluids with which it is mixed; while with 

 these are mingled gastric juice and fluid that has been swallowed, together 

 with such portions of the food as are not digestible. 



The chyme in the duodenum is subjected to the influence of the bile and 

 pancreatic juice and also to that of the succus entericus. All these secretions 

 have a more or less alkaline reaction, and neutralize the acid of the gastric 

 chyme. 



The special digestive changes in the small intestine are: (i) The fats are 

 changed by the bile and pancreatic juice in two ways, (a) They are chemically 

 decomposed by the alkaline secretions, and a soap and glycerin are the result. 

 (b) They are emulsified, i.e., their particles are minutely subdivided and dif- 

 fused, so that the mixture assumes the condition of a milky fluid or emulsion. 

 (2) The albuminous substances which have been partly dissolved in the stomach 

 are subjected chiefly to the action of the pancreatic juice. The pepsin is 

 rendered inert by the bile. The pancreatic trypsin proceeds with the fur- 

 ther conversion of the proteoses into peptones, and part of the peptones 

 (hemipeptones) into leucin, tyrosin, and other amino bodies. (3) The starchy 

 portions of the food are now acted on briskly by the pancreatic juice and 

 the succus entericus, and are changed to maltose and dextrose. (4) Salines 



