44 DIGESTION. 



IM> isolated and analyzed, a glycerin solution may.be obtained from 

 salivary glands which have been dehydrated by alcohol. This 

 ferment does not act upon any other body than starch. The action 

 of the ferment in changing starch to sugar is known as an amylo- 

 lytic action, and such a ferment is called an amylolytic ferment. 

 The kind of sugar resulting from the action of ptyalin is grape- 

 sugar or glucose, maltose being found as an intermediate step in 

 the ferment's action. 



At what age do the salivary glands become active ? 



At four to six months ; hence the reason for avoiding starchy 

 food for young infants. 



What tests are used to determine the presence of sugar and of 



starch ? 



For starch an entirely reliable and simple test is that by iodine : 

 a blue color follows the reaction ; it is a very delicate test. For 

 sugar Moore's and Fehling's tests depend upon the reduction of a 

 copper solution, and are quite delicate. The fermentation test is of 

 value in accurate quantitative determination of sugar. 



What is the action of the nervous system upon the salivary 

 glands ? 



Saliva is secreted more abundantly upon the application of a 

 stimulus. It is therefore increased by reflex nerve-force. The 

 stimuli may be mechanical or chemical or mental ; thus the flow 

 of saliva is increased by taking food into the mouth or by irritat- 

 ing the inside of the mouth by scratching or burning, or by looking 

 at or smelling or even thinking about food. 



In the submaxillary gland the chorda tympani nerve is said to 

 have a double function to increase the vascularity of the gland 

 by one portion of its fibres, and to excite the secreting function by 

 another set of fibres, the sympathetic nerves of the gland acting as 

 the vaso-constrictors. 



In the parotid the vaso-dilator impulse comes also from the facial 

 nerve through the fifth by the communication of the lesser petrosal 

 nerve. The vaso-constrictor impulse conies from the sympathetic. 



There is found a medullary centre which controls this function. 



Describe an act of deglutition. 



Deglutition, or swallowing, is the process by which we convey 

 food from the mouth to the stomach, and may be divided for the 

 purpose of analysis into three actions : 1st. The food after masti- 



