ALIMENTATION AND DIGESTION 103 



alimentary canal, a suggestion as to the proper point of view 

 will be helpful. While it is true that each part of the diges- 

 tive system performs functions of its own, it is also true that 

 what takes place in one part is dependent on what takes 

 place in others ; digestion in the mouth has reference largely 

 to subsequent work in the stomach; gastric digestion, in 

 turn, carries one step further the refinement of the food, 

 which it thereby prepares for what is to take place in the 

 small intestine ; finally, the digestive processes of the large 

 intestine are carried out normally only when preceded by the 

 proper completion of those of the small intestine. Digestion 

 is a chain of events, each one depending upon those which have 

 gone before and, to a large extent, upon others which are tak- 

 ing place at the same time. The student is urged to keep 

 this in view in the study of all the digestive processes. 



B. DIGESTION IN THE MOUTH. ENZYMES 



17. Stimulation of the sense of taste a reflex excitant of 

 the flow of gastric juice. Digestion in the mouth prepares for 

 digestion in the stomach, in the first place, by stimulating 

 the sense of taste through the flavor of the food, for the 

 afferent impulses thus aroused play a very important r61e in 

 evoking the secretion of gastric juice. This point will be 

 more fully discussed in our studies of gastric digestion. It 

 is referred to here that the student may understand that far 

 more is to be accomplished by the stay of food in the mouth 

 than its mastication and mixture with saliva preparatory to 

 the act of swallowing. We might imagine a meal composed 

 of food already well moistened and requiring no chewing, 

 so that it could be swallowed immediately. Such a meal 

 might have all the nutrients in the proper proportions, and 

 yet, from the very fact that it stays so short a time in the 

 mouth, it may not sufficiently arouse sensations of taste to 

 evoke an adequate reflex secretion of gastric juice. It is 



