228 PHYSIOLOGY OF ALIMENTATION. 



the acid upon the mucous membrane of the duodenum. 

 That this explanation is incorrect is indicated by the experi- 

 ments of POPIELSKI, WERTHEIMER, and LEPAGE, who found 

 that the introduction of acid solutions into the stomach or duo- 

 denum still excited the gland to secretion, when all the nerves 

 supplying the pancreas and duodenum had been cut. These 

 authors, nevertheless, clung to the idea of a nervous excita- 

 tion of the gland, at least in part. What had been rendered 

 probable through the experiments of POPIELSKI, WERTHEIMER, 

 and LEPAGE was made still more evident by the researches 

 of BAYLISS and STARLING, who found that it is possible to 

 isolate the pancreas from the duodenum, to divide all the 

 nerves going to a loop of the small intestine, and nevertheless 

 get a copious pancreatic secretion soon after an acid is injected 

 into this loop. 



How, then, does the acid act? The experiments of BAY- 

 LISS and STARLING l have shown that the connection between 

 intestine and pancreas is really only a chemical one. The 

 introduction of an acid into the duodenum or upper part 

 of the small intestine brings about the production of a chemi- 

 cal substance in the mucous membrane which is called secretin. 

 Since there are other secretins, it is well to call the one under 

 consideration here pancreatic secretin. As the pancreatic 

 secretin is formed it is rapidly absorbed into the blood, with 

 which it travels to the pancreas, and excites this organ to 

 secretory activity. 



Pancreatic secretin may be obtained from the upper part 

 of the intestine of any of the vertebrates. It is best pre- 

 pared by scraping off the mucous membrane of the upper 

 two feet of the small intestine, treating this in a mortar with 

 sand and 0.4 percent hydrochloric acid, and then boiling the 

 mixture. After neutralization with caustic soda the whole 

 is filtered. The clear liquid which passes through the filter 

 contains the secretin. In order to obtain the secretin in a 



1 BAYLISS and STARLING: Proceedings of the Royal Society, 1904, 

 LXXIV,p.310; STARLING: Lancet, 1905, CLX1X, pp. 339, 423, 501. 



