GASTRIC DIGESTION. 357 



The duct is lined by epithelium like that lining the stomach, while the 

 deeper part is lined by a single layer of short, fine, granular, columnar 

 cells. 



It is thus seen that the glands of the fundus and pylorus are histo- 

 logically different, and it has been found by the method of partial fistula, 

 by excising certain portions of the stomach, that the character of the 

 secretions formed b}^ these cells is also different. Here also, as in the 

 salivary glands, changes occur in the interior of the cells according as 

 the gland is active or has been exhausted. During fasting the chief 

 cells of the fundus and all the cells of the pyloric glands are clear and 

 of moderate size. During digestion the chief cells become enlarged 

 or turbid and granular ; the parietal cells also enlarge, while the pyloric 

 cells remain unchanged, and only become enlarged toward the ter- 



FIG. 149. CROSS-SECTION OF THE GLANDS OF THE FUNDUS OF THE STOMACH. 



(Heidenhain.) 

 A, through the body of the gland ; B, through the neck. 



mination of digestion. Often during the last hours of digestion the 

 chief cells again become larger and clearer, the parietal cells diminish, 

 and the p3 T loric cells decrease in size and become turbid. We therefore 

 see that there are three different forms of anatomical elements found 

 in the stomach, and these different cells furnish different forms of gastric 

 secretion (Figs. 151 and 152). When the stomach is empty its reaction is 

 alkaline and its mucous surface is covered with a layer of mucus which 

 is formed from the cylindrical epithelial cells, which line the free surface of 

 the mucous membrane and dip into the ducts of the glands. The gastric 

 juice proper comes from the tubules which line the entire stomach with 

 the exception of the cardiac and extreme pyloric ends. Gastric juice, 

 as has been seen, contains pepsin, In^drochloric acid, and the milk-curd- 

 ling ferment. The pepsin is formed by the chief cells found throughout 



