FOOD AND DIGESTION 61 



juice, succus entericus (intestinal juice) and bile. The 

 action of the three is simultaneous, but a separate de- 

 scription must be given of each to be intelligible. 



Pancreatic juice contains three ferments, trypsin, 

 amylase and lipase to act on proteins, carbohydrates 

 and fats. The pancreas is an elongated body reaching 

 from the hollow of the duodenum to the spleen and is 

 a compound tubular gland like the salivary glands. 

 Its secretion is poured through a long tube (duct of 

 Wirsung) which, after joining the common bile duct, 

 opens into the duodenum. The secretion is a clear, 

 watery fluid in man, very abundant, amounting to from 

 500 to 800 c.c. a day. The nerve supply is derived from 

 the vagus and the celiac plexus. The secretion appears 

 to begin soon after food is placed in the stomach and 

 continues from two to four hours; the first acid chyme 

 which enters the duodenum appears to incite the pan- 

 creas to activity. This activity is probably not pro- 

 duced by reflex nerve action, but by the production of 

 a chemical body, secretin, which is absorbed by the 

 blood, carried to the pancreas and stimulates the organ. 

 A similar explanation is given of the secretion of gas- 

 tric juice. Bodies which are thus formed and act in 

 this manner are termed hormones. The character of the 

 food determines the type of the secretion; i.e., if meats 

 alone are eaten the juice will be rich in trypsin ; if fats, 

 in lipase; if bread, in amylase. 



Trypsinogen alone, the immediate enzyme of the pan- 

 creas, is not able to act on proteins but requires the 

 presence of another substance, kinase or entcrokinase, 

 which is formed by. the mucous membrane of the small 

 intestine, by which it is converted into trypsin. 



Trypsin differs from pepsin in the following particu- 



