246 



ELEMENTARY PHYSIOLOGY 



the tubes they are cubical and slightly granular. These are 

 the central cells(Fig. 77, c). Asecondkind of cell inayalso 

 be seen lying irregidarly scattered between the outer wall 

 of the gland and its central cells : these are the parietal 

 or ovoid cells (Fig. 77, p). 

 Oval in shape, they have a well- 

 defined outline and their cell- 

 substance is usually very distinctly 

 granular. The glands near the 

 pyloric end of the stomach differ 

 from those of the rest of the mucous 

 membrane, chiefly and essentially 

 by not containing any of these 

 ovoid cells. 



When the stomach is empty, its 

 nnicous membrane is pale and 

 hardly more than moist. Its small 

 arteries are then in a state of con- 

 striction, and comparatively little 

 blood is sent through it. On the 

 entrance of food a vaso-motor action 

 is set u|), which causes these small 

 arteries to dilate ; the nmcous mem- 

 brane consequently receives a much 

 larger quantity of blood, and it 

 becomes very red. At the same 

 time the cells of the gland begin 

 to form their secretion, taking the 

 material they require for this pur- 

 pose out of the extra supply of 

 blood now coming to them. The 

 whole process is exactly similar in 

 principle to that already described 

 in the case of the secretory activity of the submaxillary 

 gland (p. 242). 



The secretion thus formed is the gastric juice. 



Fio. 77.— One of the 

 Glands which Se- 

 cretes Gastric Juice. 

 I), the duct or mouth 

 of the gland ; m, mucous 

 cells liniug the mouth of 

 the gland and covering 

 the inner surface of the 

 mucous membrane ; c, 

 central cells ; p, parietal 

 or ovoid cells. 



