710 



PHYSIOLOGY OF DIGESTION AND SECRETION. 



juice and are not digested. If such articles of food are eaten, 

 however, they cause a psychical secretion, and when this has acted 

 upon the foods some products of their digestion in turn become 

 capable of arousing a further flow of gastric juice. The steps in 

 the mechanism of secretion are, therefore, three: (1) The psychical 

 secretion; (2) the secretion from secretogogues contained in the 



food; (3) the secretion 

 from secretogogues 

 contained in the 

 products of digestion. 

 The manner in which 

 the secretogogues act 

 cannot be stated posi- 

 tively. Since the gas- 

 tric glands possess 

 secretory nerve fibers 

 the first explanation 

 to suggest itself is 

 that the secreto- 

 gogues by acting on 

 sensory fibers in the 

 gastric mucous mem- 

 brane reflexly stimu- 

 late the secretory 

 fibers. This expla- 

 nation, however, is 

 rendered untenable 

 by the fact that the 

 effect of these sub- 

 stances is obtained 

 after complete sever- 

 ance of the nervous 

 connections of the 

 stomach. If, there- 

 fore, this so-called 

 chemical secretion is 



Quantity of secretion. 



-___ Acidity. 



_ Digestive power. 



Fig. 271. Diagram showing the variation in quantity 

 of gastric secretion in the dog after a mixed meal ; also 

 the variations in acidity and in digestive power. (After 

 K h igine.) 



produced by a ner- 

 vous reflex the nerve centers concerned must lie in the stomach 

 itself, the reflex must take place through the peripheral ganglion 

 cells. Another more probable explanation has been offered. 

 Edkins * has shown that decoctions of the pyloric mucous mem- 

 brane, made by boiling in water, acid or peptone solutions, 

 when injected into the blood cause a marked secretion of gastric 

 juice. These substances when injected alone into the blood cause 

 * Edkins, " Journal of Physiology," 1906, xxxiv., p. 133. 



