346 FOOD AND DIGESTION 



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 a mineral acid, hydrochloric acid in the ducts 

 and intracellular canals of the parietal oxyntic cells. The pyloric cells do 

 not undergo such marked changes, and the mucous cells of the more super- 

 ficial 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 Pawlow 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. 



