1 62 Physiology. 



as we say, i.e. the salivary glands are, by reflex action, 

 stimulated to activity ; on the other hand, some emotions, 

 such as fear, check the flow of saliva. 



Saliva and its Uses. The saliva is mostly water, and, 

 when we are not eating, serves ( I ) to keep the mouth moist. 

 The water of the saliva soaks the food during mastica- 

 tion and (2) helps the process of grinding; it (3) enables 

 us to taste by dissolving any food that is soluble ; it 

 further (4) enables us to swallow what would otherwise 

 be a dry powder. The special element of the saliva, 

 ptyalin, has the power (5) of changing starch to sugar. 



Amount of Saliva. The amount of saliva secreted 

 daily is estimated at three pints. Of course the glands 

 should be allowed to rest between meals. The habit of 

 chewing gum, though supposed to aid digestion, undoubt- 

 edly does far more harm than good. During the resting 

 period the glands accumulate material for the active work 

 of secretion, for there is no sac in which to store the 

 saliva, and it must be made as fast as is needed. 



Mucous Glands and Mucus. Besides the salivary glands, 

 there are great numbers of simple glands in the mucous 

 membrane lining the mouth. These secrete a clear sub- 

 stance called mucus, resembling white-of-egg. It is mucus 

 in saliva that makes it "stringy." 



Mumps. In the mumps the salivary glands are in- 

 flamed and painful. This is most noticeable in the 

 parotid gland, which feels the pressure of the lower jaw 

 in the attempt to chew. 



Effect of Alcohol on the Throat. M. Lanceraux, a 

 French authority, says that the use of alcoholic drinks 

 produces a softening of the salivary glands, together with 



