114 THE HUMAN MECHANISM 



This brief sketch of the working of the stomach shows 

 that this organ serves the two main functions of storing the 

 food and of making it more accessible to the digestive fluids 

 of the intestine. When the chyme is delivered to the intes- 

 tine, the mechanical difficulties in the way of absorption are 

 practically gone ; the surface of the food exposed to diges- 

 tive action is now immensely increased by its subdivision, 

 and the work remaining for the intestine is almost wholly 

 the chemical duty of changing the constituents of the chyme 

 into substances which are soluble and ready for absorption. 



Serious troubles arise when, for one reason or another, 

 gastric digestion goes wrong, because the subsequent proc- 

 esses of digestion are largely dependent upon the preparation 

 which the food receives in the stomach. Gastric digestion 

 may be impaired in one of three ways : first, the gastric 

 juice may not be secreted in proper amount or proper 

 strength; second, the stomach may not execute its move- 

 ments efficiently ; third, the gastric juice secreted may not 

 be able to get at the food readily, owing to improper cook- 

 ing or insufficient mastication. The study of the conditions 

 which produce these troubles which taken together consti- 

 tute one form of indigestion, or dyspepsia will be postponed 

 to the chapter on the Hygiene of Feeding (Part II). 



24. The stimulus to the secretion of the gastric juice. The 

 first requirement for the work of the stomach is the secre- 

 tion of sufficient gastric juice. Of late years the brilliant 

 researches of physiologists have shown that the secretion of 

 gastric juice is called forth in three ways : 



1. The "psychic" secretion. When agreeable or appetizing 

 food is offered to an animal, and especially when such food 

 is taken into the mouth, a secretion of gastric juice follows, 

 which may continue for fifteen minutes or more. This secre- 

 tion occurs when the food has been in the mouth only ten 

 or fifteen seconds and even when it is merely offered to a 

 hungry animal and not taken into the mouth at all. Again, 



