THE DIGESTIVE SYSTEM. 

 PANCREATIC SECRETION AFTER A MEAL OF 600 c.c. OF MILK. 



317 



Bayliss and Starling have shown that the secretion of pancreatic 

 juice is almost entirely due to a hormone, which they have called 

 secretin, and which is formed in the mucous membrane of the small 

 intestine. The production of the hormone is brought about by the 

 presence of acid in the intestine, and the normal stimulus for its 

 formation is the passage of the acid gastric contents into the duodenum. 



Much work has been done with a view to determining whether a 

 nervous factor is concerned in the production of pancreatic juice, 

 comparable with the reflex which brings about the first secretion of 

 gastric juice ; and Pawlow has shown that stimulation of the vagus will 

 excite a small flow of pancreatic juice, even when the pylorus of the 

 stomach is ligatured so as to prevent the passage of the acid contents of the 

 stomach into the duodenum. The amount secreted as the result of vagus 

 stimulation is, however, so small that the nervous factor is obviously 

 of subsidiary importance in the case .of the pancreas. It is possible 

 that the first few c.c. of juice secreted may be nervous in origin, because 

 the juice first formed appears a few minutes after a meal is taken, and 

 further, it differs in character from the later formed juice, being more 

 viscid, richer in ferments and in protein constituents and poorer in 

 alkali than the latter. 



The later flow is, however, the essential secretion, and that it is due 

 to the formation of a hormone is proved by experiment. If 0'4 per cent, 

 hydrochloric acid is introduced into the duodenum, a flow of pancreatic 

 juice is evoked within two or three minutes. The secretion induced in 

 this way occurs even if the nerves to the intestine have been divided, so 

 that it must be due to the production of some chemical substance which 

 is conveyed to the pancreas. This substance is secretin, and it may be 

 extracted from the duodenal mucous membrane by grinding it with sand 

 and boiling with 0'4 per cent, hydrochloric acid. If alkali be added to 



