ORGANS AND PROCESSES OF DIGESTION 145 



consists chiefly of water (about 99 per cent), but in this are 

 dissolved certain salts and an active chemical agent, or 

 enzyme, called ptyalin, which acts on the starch. The 

 ptyalin changes starch into a form of sugar (maltose), 

 while the water in the saliva dissolves the soluble portions 

 of the food. In addition to this the saliva moistens and 

 lubricates the food which it does not dissolve, and prepares 

 it in this way for its passage to the stomach. The last is 

 considered the most important use of the saliva, and dry 

 substances, such as crackers, which require a considerable 

 amount of this liquid, cannot be eaten rapidly without 

 choking. Slow mastication favors the secretion and action 

 of the saliva. 



Deglutition. Deglutition, or swallowing, is the process 

 by which food is transferred from the mouth to the stomach. 

 Though this is not, strictly speaking, a digestive process, it 

 is, nevertheless, necessary for the further digestion of the 

 food. Mastication and insalivation, which are largely 

 mechanical, prepare the food for certain chemical processes 

 by which it is dissolved. The first of these occurs in the 

 stomach and to this organ the foo,d is transferred from 

 the mouth. The chief organs concerned in deglutition are 

 the tongue, the pharynx, and the esophagus. 



The Pharynx is a round and somewhat cone-shaped 

 cavity, about four and one half inches in length, which 

 lies just back of the nostrils, mouth, and larynx. It is 

 remarkable for its openings, seven in number, by means 

 of which it communicates with other cavities and tubes of 

 the body. One of these openings is into the mouth, one 

 into the esophagus, one into the larynx, and one into each 

 of the nostrils, while two small tubes (the eustachian) pass 

 from the upper part of the pharynx to the middle ears. 



The pharynx is the part of the food canal that is crossed 



