150 MANUAL OF PHYSIOLOGY. 



When yeast is added to grape sugar and placed in an inverted 

 test tube, the sugar is converted into alcohol and carbon dioxide. 

 The latter rises to the top of the test tube, and can be used as an 

 indication of the quantity present. Experiments may be carried 

 out with saliva obtained from any of the glands directly, but the 

 mixture of the secretion of all is found to be more efficacious than 

 that of any single one. The ordinary mouth fluid filtered serves 

 well for ordinary experiment. 



An effective glycerin solution of ptyalin may be obtained by 

 steeping chopped salivary glands in alcohol, and then extracting 

 for some days with glycerin and water. 



The following facts must be borne in mind concerning the 

 amylolytic action of ptyalin : 



1. The extremely small amount of the ferment required to 



make the fluid effective. 



2. There is no appreciable diminution in the amount of fer- 



ment, so that it cannot be said to be used up in the 

 process. 



3. The action takes place most readily in alkaline solutions, 



such as the saliva, slowly in neutral solution, and not at 

 all in acids of the strength of .2 per cent, of hydrochloric 

 acid. 



4. Temperature has a marked effect on the process. Cold 



(0 C.) quite checks the action ; heat (75 C.) destroys 

 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, itsjcellulose 



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 place 

 in the mouth : 



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

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



