214 



GASTRIC GLANDS. 



Mouth of Gland 



Epithelium 



quarts. Of course, we must bear in mind that nearly all of 

 this is again absorbed from the digestive tube, and is not a 

 permanent loss to the body. 



The mucous membrane is abundantly supplied with blood 

 tubes ; but during the time of its rest the blood flow here is 

 diminished, and the membrane is comparatively pale. But as 

 soon as food is introduced into the stomach, the blood flow is 

 greatly increased, and the mucous membrane becomes red. 

 This blood supply gives the glands the materials with which 

 they manufacture the gastric juice. At the same time the 



cells of the glands are stim- 

 ulated to action, and the 

 secretion is poured out 

 rapidly. The alkaline sa- 

 liva also aids in stimulating 

 the secretion of the gastric 

 juice. The special 

 work of the gastric 

 juice is accom- 

 plished by the pepsin, aided 

 by the acid; these convert 

 proteids into a soluble sub- 

 stance, called Peptone, which 

 can be absorbed through the 

 walls of the digestive tube 



into the blood. Eennet, used in cheese-making, is a famil- 

 iar substance obtained from the fourth stomach of the calf. 

 Now, when milk enters the human stomach it is curdled ; 

 that is, the casein previously dissolved in the liquid milk is 

 coagulated. This curdling, or coagulation, is attributed to a 

 ferment in the gastric juice called Rennin ; and it seems to 

 be entirely distinct from pepsin. At the same time all the 

 food is soaked by the gastric juice, the process being greatly 



Principal, 



Cells 



Connective Tissue 



Fig. 81. Three Glands of the Stomach 

 Cardiac Part 



