I'l PHYSIOLOGY FOR DENTAL STUDENTS. 



stance to be added to the blood, which then carries it to the pan- 

 creas and liver, upon the cells of which it exercises a stimulating 

 influence. That this is the correct explanation was shown by 

 studying the effect which is produced on the secretion of pan- 

 creatic juice and bile by intravenous injections of decoctions of 

 intestinal mucosa made with weak acid and subsequently neu- 

 tralized. An immediate secretion resulted. The acid extract evi- 

 dently contained some hormone whose production, in the normal 

 process of digestion, is evidently occasioned by the contact of the 

 acid chyme with the duodenal mucosa. This hormone is called 

 secretin but we know very little of its exact chemical nature. It 

 is not a ferment, for it withstands heat ; it is not a protein, for it 

 can be extracted by boiling the mucous membrane with weak 

 acids after treatment with alcohol. It is readily oxidized in the 

 presence of alkalies, and is of the same nature in all animals. 

 It is useless to give secretin as a drug with the hope that it will 

 stimulate pancreatic secretion, for it is not absorbed from the 

 lumen of the intestine. 



Although most abundant in the mucosa of the duodenum and 

 jejunum, secretin is also present in the mucosa of the lower end 

 of the small, and to a lesser degree, in that of the large intestine. 

 Soap solutions act like acid in producing secretin. A fatty meal, 

 therefore, excites the flow of much pancreatic juice and bile, be- 

 cause the fatty acid which is split off unites with alkali and 

 forms soap. 



It may be that the very first portion of pancreatic juice to be 

 secreted after a meal is taken, is due, not to secretin formation, 

 but to reflex nervous stimulation of the pancreas. In comparison 

 with the hormone control the nervous control is, however, quite 

 unimportant in pancreatic secretion, for there is no necessity in 

 the intestine, as in the mouth, or to a less degree in the stomach, 

 for a quick response to the stimulus produced by the presence 

 of food. The histological changes produced in the gland cells of 

 the pancreas by secretory activity are much the same as in the 

 parotid glands. 



Functions of the Bile and Pancreatic Juice. These 1\vo 

 juices are very closely associated in their activities. This fact 



