188 CHEMICAL MECHANISMS OE SECRETION 



which is insoluble in water and alkalies and is not destroyed by 

 boiling alcohol. 



4. Secretin is not a ferment. It withstands boiling in acid, 

 neutral, or alkaline solutions, but is easily destroyed by active 

 pancreatic juice or by oxidising agents. It is not precipitated 

 from its watery solutions by tannic acid, or alcohol and ether. 

 It is destroyed by most metallic salts. It is slightly diffusible 

 through parchment paper. 



5. The pancreatic juice obtained by secretin injection has no 

 actions on proteids until " enterokinase " is added. It acts on 

 starch and to some extent on fats, the action on fats being increased 

 by the addition of succus entericus. It is, in fact, normal pan- 

 creatic juice. 



6. Secretin rapidly disappears from the tissues, but cannot 

 be detected in any of the secretions. It is apparently not absorbed 

 from the lumen of the intestine. 



7. It is not possible to obtain a body resembling secretin from 

 any tissues of the body other than the mucous membrane of the 

 duodenum and jejunum. 



8. Secretin solutions, free from bile salts, cause some increase 

 in the secretion of bile. They have no action on any other 

 glands. 



9. Acid extracts of the mucous membrane normally contain 

 a body which causes a fall of blood pressure. This body is not 

 secretin, and the latter may be prepared free from the depressor 

 substance by acting on desquamated epithelial cells with acid. 



The Chemical Mechanism of Gastric Secretion Gastrin. It has 

 long been known that the introduction of certain substances into 

 the stomach provokes a secretion of gastric juice, and the effect 

 has been ascribed to a nervous mechanism stimulated by the effect 

 of absorbed substances upon peripheral nerve-endings in the gastric 

 mucosa. Quite recently, however, it has been shown by Edkiris,, 

 that intravenous injection of extracts prepared in special manner 

 from certain parts of the gastric mucous membrane leads to a 

 flow of gastric juice. Edkins considers this action to be due to 

 a substance which he has named gastrin, and which acts as a 

 chemical excitant or " hormone " for the gastric secretion, in a 

 similar fashion to secretin in the case of the pancreatic juice. It 

 is hence possible that those substances shown by Pawlow to excite 

 the gastric secretion when introduced into the stomach so as not 



