142 MANUAL OF PHYSIOLOGY. 



the power of the ferment, which is most active at the 

 body temperature (35-40 C.). 



5. Strong acids or alkalies destroy the amylolytic power of 



ptyalin. 



6. The ferment has but little effect on raw starch, its cellulose 



coating protecting it; but it acts rapidly on well-boiled 

 starch. 



7. Ptyalin is more active in weak solutions, and seems to be 



impeded in its action by an accumulation of sugar. 



To recapitulate, we find that the following changes take phu-o 

 i n the mouth : 



(1) Solid food is or should be finely subdivided ; (2) dry 

 food is moistened, (3) rolled into a bolus, (4) and 

 lubricated ; (5) the soluble part is dissolved, and 

 rendered capable of being tasted ; (6) and part of the 

 starch is converted into soluble sugar by the action 

 of a ferment called ptyalin. 



In the short time occupied by the passage of food through the 

 oesophagus no special change takes place in it, so we may pass on 

 at once to the gastric digestion, which will occupy the next 

 chapter. 



