DIGESTION IN THE SMALL INTESTINE 397 



1. The diastase does not appear in the juice until a month after 

 birth, trypsin being present from the start. 



2. Trypsin can be precipitated and separated from the other 

 enzymes by addition of collodion. 



It was at one time stated that the enzymic content of the juice was 

 not only modified to meet the nature of the food, but, if necessary, 

 new enzymes were manufactured to digest fresh articles of food in 

 the diet. For example, on a mixed diet, the pancreatic juice contains 

 no lactose-splitting enzyme (lactase). It was said that, with the 

 introduction of a milk diet, a lactase became secreted in the pancreatic 

 juice. The experimental evidence is now against this view, and by 

 some workers the adaptation to the diet of the enzymic content of 

 the juice is seriously called in question. 



The juice is said by some to contain several other enzymes, in 

 particular a nuclease (nucleic-acid-splitting enzyme). Traces of 

 erepsin, maltase, and lactase have been found. 



Fia. 197. To SHOW EFFECT OF INJECTION OF SECRETIN. (Bayliss and Starling.) 

 A, Blood-pressure; B, drops of pancreatic juice; C, drops of bile. 



The Mechanism of Secretion. Reference has been made to the 

 " hormone," or chemical mechanism of secretion. " Secretin " is 

 stored as pro-secretin, especially in the duodenal mucous mem- 

 brane, and in less amount in the jejunum. In the ileum there is 

 none. 



To prepare it the mucous membrane is scraped from a piece of 

 small intestine, thoroughly minced, and ground up with sand in a 

 mortar. The whole is then treated with 0-3 per cent, hydrochloric 

 acid, and boiled. This coagulates the proteins and extracts the 

 secretin, which is not destroyed by boiling. The clear fluid is filtered 

 off, carefully neutralized, and used for intravenous injection to pro- 

 voke pancreatic secretion (Figs. 197, 198). Secretin is soluble in 

 alcohol and ether. 



Not only acid, but water and oil call forth, by their presence in 

 the intestine, a flow of pancreatic juice. So do such bodies as 

 pepper, mustard, and alcohol. Soaps have a particularly potent 



