VII THE DIGESTIVE SYSTEM AND ITS FUNCTIONS 147 



to obtain no decisive evidence of such preliminary increase 

 in granulation although he was not disposed to deny that it 

 might take place at least to a slight extent. 



Of what significance are these changes in the granular 

 contents of the gland cells? It is evident that they have 

 something to do with the formation of digestive fluids 

 of the esophagus and stomach, and it is probable that the 

 granules are composed of a substance which is transformed 

 into pepsin. That they are not composed of pepsin itself, 

 but of some substance which has been called pepsinogen, is 

 indicated by the following experiments. "If the esophagus 

 or stomach of a frog be placed in glycerin as rapidly as 

 possible after removal from the body, the glycerin extract 

 has only a weak peptic power. If the esophagus or stomach 

 of a frog be kept moist for twenty hours before it is placed 

 in glycerin, the glycerin extract has a very much greater 

 peptic power. If the esophagus and stomach which has 

 been extracted with, say, 5 cu. cm. of glycerin for a week 

 be washed free of glycerin and treated with 5 cu. cm. of 

 dilute hydrochloric acid, then an enormously greater amount 

 of pepsin is found in the acid than is found in the glycerin 

 extract." 



The amount of pepsin content is greatest in those glands 

 in which there is the greatest number of granular cells. 

 The pepsin content of the esophagus was found by Swiecicki, 

 Langley, and Sewall to be greater than that of an equal area 

 of the stomach. In the pyloric region, where the granular cells 

 are few in number, the pepsin content of the glands is much 

 less than in the cardiac end. Langley found that if pieces of 

 equal size were cut out of the esophagus, cardiac end, mid- 

 dle, and pyloric end of the stomach, and the pepsin content 

 of each estimated, the power of converting proteid was much 

 the greatest from the piece from the esophagus, and became 



