ACT OF SECRETION OF GASTRIC JUICE 365 



membrane. From this superficial network the veins chiefly take their origin, 

 pass down between the tubes, with no very free connection with the deeper 

 intertubular capillary plexus, and open finally into the venous network in 

 the submucous tissue. 



The lymphatic vessels surround the gland tubes with a network. 

 Toward the fundus of the peptic glands are masses of lymphoid tissue 

 which may appear as distinct follicles, somewhat like the solitary glands 

 of the small intestine. 



Microscopic Changes in the Gastric Glands During Secretion. 

 Langley 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 dis- 

 charge 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. Macallum by the use of microchemical 

 tests has shown the presence of excess of chlorides in the ducts and in- 

 tracellular canals, and in the parietal 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 the dog with a gastric fistula. Such 

 observations strongly indicate that the act is a nervous phenomenon, at least 

 under nervous control. 



Quite recently Pavlov has proved that secretory fibers are carried to 

 the gastric glands in the vagus trunk. His experiment consisted in estab- 

 lishing a gastric fistula, and some days later in dividing the esophagus 

 in the neck in such a manner that any food swallowed would be diverted 

 to the exterior through the cut end. A " fictitious meal" could then be given 

 to the animal, and the effect upon the stomach noted. As long as the vagi 

 were intact, certain foods (meats) caused a flow of gastric juice, though 

 none of the food reached the stomach. The secretion of gastric juice con- 

 tinued for hours with the production of a large quantity of secretion. When 

 the vagi had been cut, no secretion occurred. Moreover, he found that direct 

 stimulation of the vagus produced a flow of gastric juice. 



Khigine placed foods in an isolated gastric pouch prepared with care to 



