THE PANCREATIC JUICE 797 



concluded that these two nerves splanchnics and vagi were the 

 efferent channels in the reflex secretion set up by the introduc- 

 tion of the acid into the duodenum. It was shown later, however, 

 independently, both by Popielski, a pupil of Pawlow, and by 

 Wertheimer, that the injection of acid into a loop of small intestine 

 was followed by secretion of juice even after section of both vagi 

 and destruction of the sympathetic ganglia at the back of the abdominal 

 cavity. On repeating these experiments Bayliss and Starling found 

 that a secretion of juice was produced even when the acid was intro- 

 duced into a loop of the small intestine entirely freed from any 

 possible nervous connections with the rest of the body. It was 

 evident therefore that the stimulus or message from the intestine 

 to the pancreas which causes the secretion of the latter must be 

 carried, not by the nervous system, but by the blood stream. Since 

 the injection of acid into the portal vein was without effect on the 

 pancreas, it was evident that something must be produced in the 

 epithelial cells of the gut under the influence of acid, and that this 

 product of the epithelial cells was absorbed in the blood stream and 

 was the active agent in exciting the pancreas. On pounding up 

 some scrapings of the intestinal mucous membrane with dilute 

 hydrochloric acid and filtering, and injecting the filtrate, a copious 

 flow of pancreatic juice was produced. This chemical messenger 

 or hormone from the intestine to the pancreas is called ' secretin/ 

 or ' pancreatic secretin ' to distinguish it from possible other members 

 of the same class. It is produced in the mucous membrane from 

 a precursor pro-secretin. The latter has not been isolated, but that 

 it is present in the mucous membrane is shown by the fact that 

 secretin can be extracted by the action of acids from mucous membrane 

 which has been killed by heat or by the prolonged action of alcohol. 



Secretin itself is not a ferment. In order to prepare it the mucous 

 membrane is ground up with sand, boiled with 0-4 per cent, hydro- 

 chloric acid, and then neutralised while boiling by the cautious 

 addition of sodium hydrate. The coagulable proteins are in this 

 way precipitated, and the filtered solution contains the secretin. 

 It is not precipitated by the ordinary alkaline reagents, and diffuses 

 slowly through animal membranes. Though stable in acid solutions, 

 it is very rapidly destroyed in alkaline or neutral solutions, especially 

 under the influence of bacteria. It is apparently oxidised with 

 extreme ease. A similar, or more probably the same, body may be 

 produced from intestinal mucous membrane by treating this with 

 solutions of soap. 



In this secreting mechanism we have a very striking example 

 of a correlation between the activities of two different portions of 

 the body effected by chemical means. The strongly acid chyme 



