320 



POOD AND DIGESTION 



Microscopic Changes in the Gastric Glands During Secretion. Lang- 

 ley has made a study of the histological changes in the glandular tissues 

 in the fresh state. He finds that during fasting or when the glands are at rest 

 the chief cells are granular throughout, being crowded with large highly re- 

 fractive granules. During activity these granules gradually disappear pro- 

 gressively from the base toward the border of the cell on the lumen of the tube. 

 They no doubt represent the zymogen substances from which the first discharge 



FIG. 258. Scheme of Blood-vessels and Lymphatics of Stomach. X 70. a, Mucous mem- 

 brane; b, muscularis mucosae; c, submucosa; d, inner circular muscle layer; e, outer longitudinal 

 muscle layer; A, blood-vessels; B, structure of coats; C, lymphatics. (Szymonowicz, after Mall.) 



of enzyme is derived during the activity of secretion. The parietal cells are 

 finely granular throughout, though they decrease in size during activity, as in 

 fact do the chief cells. The pyloric cells do not undergo such marked changes, 

 and the mucous cells of the more superficial layers of the mucosa cannot be 

 said to show any special changes at the time of digestional activity of the 

 other layers. During periods of rest the gastric cells increase in size and 

 again become charged with granules as before. 



The Act of Secretion of Gastric Juice. The gastric glands un- 

 dergo periods of rest and activity. The active secretion of normal gastric 

 juice takes place when food is introduced into the mouth, or in fact the 

 mere sight of appetizing food is followed by an abundant secretion of gastric 

 juice as shown by Bidder and Schmidt on a dog with a gastric fistula. Such 



