690 



PHYSIOLOGY OF DIGESTION AND SECRETION. 



gastric 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 product of their digestion in turn becomes ca- 

 pable of stimulating the secretory paths by a reflex from the stomach. 

 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 chemical nature 

 of these last-named 

 stimuli is undeter- 

 mined. 



The researches of 

 Pawlow and his co- 

 workers seem also to 

 indicate that the 

 quantity and prop- 

 erties of the secre- 

 tion vary with the 

 character of the food. 

 The quantity of the 

 secretion varies, also, 

 other conditions be- 

 ing the same, with 

 the amount of food 

 to be digested. The 

 apparatus is adjusted 

 in this respect to 

 work economically. 

 Different kinds of 

 food produce secre- 

 tions varying not 

 only as regards quan- 

 tity, but also in their 

 acidity and digestive 

 action. The secre- 

 tion produced by 

 bread, though less in 

 quantity than that caused by meat, possesses a greater digestive 

 action. On a given diet the secretion assumes certain characteris- 

 tics, and Pawlow is convinced that further work will disclose the fact 

 that the secretion of the stomach is not caused normally by general 

 stimuli all affecting it alike, but by specific stimuli contained in the 

 food or produced during digestion, whose action is of such a kind 

 as to arouse reflexly the secretion best adapted to the food ingested. 



Quantity of secretion. 



Acidity. 



Digestive power. 



Fig. 262. 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 

 Khigine.) 



