SECRETION OF THE GASTRIC AND INTESTINAL MUCOSA 439 



fuse pancreatic secretion. To this active substance, which is not 

 a ferment because it withstands boiling and is soluble in alcohol, 

 they gave the name of " secretin." Bayliss and Starling 

 assumed that, by the hydrolytic action of the acids, secretin is 

 formed from " prosecretin," a precursor present in the cells 

 of the duodenal mucous membrane. The secretin formed in the 

 mucosa reaches the pancreas by way of the blood-stream ; for 

 Enriquez and Hallion succeeded in proving that, if the blood- 

 stream is conveyed from the vessels of a dog A into those of a 

 dog B, pancreatic secretion will make its appearance in B after 

 the injection of acid into the small intestine of A. These experi- 

 ments proved the existence of an internal secretion of the intestinal 

 mucosa, and they showed at the same time that there is a correla- 

 tion of function between the intestinal mucosa and the pancreas, 

 which is effected by the agency of hormones. 



Bayliss and Starling's discovery has been subjected to 

 repeated tests, and the actual findings have received almost general 

 confirmation. The specific activity and the intimate chemical 

 nature of secretin have formed the subjects of a controversy, into 

 the details of \\hich we cannot enter here. Suffice it to say that 

 Popielski believes secretin to be identical with peptone, a product 

 of the decomposition of albumin ; while according to v. Fiirth 

 and Schwarz, secretin is not a homogeneous substance, but is a 

 mixture of several substances possessing the property of exciting 

 secretion, of which the most important is cholin. 



A far greater interest is attaching to the manner in which this 

 discovery affects our conception of the mechanism by which the 

 external secretion of the pancreas is effected. Is the secretory 

 process entirely due to the agency of a hormone, as Bayliss and 

 Starling are inclined to believe ; or are the nervous reflexes, which 

 Pawlow's experiments revealed, also brought into play? This 

 question remains for the present unanswered. Several authors 

 (Fleig) assume, and apparently with justice, that two simultaneous 

 processes are concerned in the passage of the chyme into the 

 duodenum. Of these, one is the formation of secretin, which 

 induces, by chemical means, secretion of the pancreas; the other 

 is provided by the acid contents of the duodenum, which stimulate 

 the nerve-terminals, and the reflex action of these also leads to 

 pancreatic secretion. 



According to Bayliss and Starling, the secretin formed in 

 the duodenal mucosa stimulates the secretion of bile and increases 

 its quantity. 



With regard to the secretion of the intestinal juice, the succus 

 entericus, opinions are divided. The intestinal juice serves to 

 activate the proteolytic property of the pancreatic secretion, for 

 the trypsinogen contained in the latter is converted into the active 

 trypsin ferment by the agency of the endokinase in the intestinal 

 juice. The elaboration of the intestinal secretion is effected, 



