106 DIGESTION 



ting the food for swallowing. It is impossible to swallow 

 dry food, and the moistening with the saliva makes this ac- 

 tion possible, and at the same time acts as a lubricant and 

 allows it to slip down more easily. In fact, so short is 

 the time that food spends in the mouth in ordinary eating 

 that probably very little starch is changed into sugar 

 there, and the mechanical action, therefore, is the most 

 important. Saliva, as we shall see later, also aids in 

 producing the sensation of taste. 



SuMMABY OP Digestion in the Mouth. 



1. The teeth grind the food into small particles and fit it for 

 rapid and thorough mixing with the saliva. (Mastication.) 



2. The tongue rolls the food about into position for mastication 

 and mixes it with the saliva. 



3. The saliva through the action of the ptyalin enzyme con- 

 verts part of the starch into soluble sugar. 



4. The saliva moistens and lubricates the food mass and thus 

 fits it for swallowing. 



5. The food leaves the mouth in proper shape for the action of 

 other juices and with part of its starch converted into sugar. 



