30 



HUMAN PHYSIOLOGY. 



The secretion of gastric juice is a reflex act, taking place through the 

 central nervous system and called forth in response to the stimulus of food 

 in the stomach. That the central nervous system also directly influences 

 the production of the secretion is shown by the fact that mental emotion, 

 such as fear and anger, will arrest or vitiate the normal secretion. The 

 reflex nature of the process can be shown by experimentation upon the 

 pneumogastric nerve. If during digestion, when the peristaltic movements 



FIG. 3. 



Diagram showing the relation of the ultimate twigs of the blood vessels, V and A, and 

 of the absorbent radicles to the glands of the stomach and the different kinds of epi- 

 thelium, viz., above cylindrical cells: small, pale cells in the lumen, outside which 

 are the dark ovoid cells. From Yea's Text-Book of Physiology. 



are active and the gastric mucous membrane flushed and covered with 

 gastric juice, the pneumogastric nerves are divided on both sides, the 

 mucous membrane becomes pale, the secretion is arrested and the peristaltic 

 movements become less marked. Stimulation of the peripheral end produces 

 no constant effects; stimulation of the central end, however, is at once 

 followed by dilatation of the vessels, flushing of the mucous membrane and 

 a re-establishment of the secretion. It is evident, therefore, that during 



