60 INTERNAL SECRETION 



membrane, rubbed it up with sand and 04 per cent. HC1 in a 

 mortar, filtered and injected into a vein. The first effect was a 

 considerable fall of blood-pressure, and, after a latent period of 

 about twenty seconds, a flow of pancreatic juice at more than 

 twice the rate produced at the beginning of the experiment by 

 introduction of acid into the duodenum. 



Bayliss and Starling suggest the name " secretin " for the 

 active substance present in the intestinal extract, and the 

 term has been adopted by subsequent workers. Secretin is 

 probably produced by a process of hydrolysis from a pre- 

 cursor " prosecretin " present in the intestinal cells. It is 

 not a ferment, nor is it of the nature of an alkaloid or 

 diamino-acid. 



The results obtained by Bayliss and Starling were confirmed 

 by Camus and Gley and others, and Wertheimer demonstrated 

 the presence of secretin in the blood flowing from a loop of 

 intestine into which acid has been introduced. 



In a later communication Bayliss and Starling announced 

 that secretin can be prepared from the upper part of the in- 

 testine of any animal belonging to the class of vertebrata by 

 scraping off the mucous membrane, pounding it up, and boiling 

 with dilute hydrochloric acid. 



The experimental evidence which is clearly put before us by 

 Bayliss and Starling justifies the view that the normal sequence 

 of events in the secretion of juice by the pancreas is as follows : 

 The acid of the gastric juice upon reaching the duodenum 

 converts the prosecretin manufactured by the epithelial cells 

 into secretin ; this secretin is then absorbed into the blood- 

 stream, carried to the cells of the pancreas, and stimulates the 

 organ to secretory activity. The external secretion of the 

 pancreas is the result of the internal secretion of itie duodenal 

 mucous membrane. 



The formation of prosecretin in the duodenum does not 

 appear to take place as a response to the stimulus of ingestion 

 of food. Pringle has quite recently found that secretin 

 prepared from newly-born kittens, before suckling, gives 

 a fairly active flow of juice when tested on a dog. When 

 foetuses of different periods were examined, it was found 

 that some showed the presence of an active secretin, some 

 did not. 



In tli is most important discovery of Bayliss and Starling is 



