SALIVA 121 



help in the grinding process. During this process the food is 

 thoroughly mixed with secretions from the glands of the 

 mouth. 



The chief secretion of the mouth is supplied by the salivary 

 glands. These are three pairs of compound saclike glands, the 

 parotid, sublingual, and submaxillary. A parotid gland is placed 

 just under and in front of each ear; the ducts from the glands 

 pass forward along the cheek and open opposite the second molar. 

 The submaxillary glands are situated below the jaw and under the 

 tongue, and open into the mouth cavity underneath the tongue. 

 Several of the small ducts from the sublingual glands also open in 

 the floor of the mouth beneath the tongue. The secretion of these 

 salivary glands, mixed with the secretion of the small glands of 

 the mucus epithelium, is called saliva. 



Everyone has probably experienced an unusually large flow of 

 secretion from the salivary glands when appetizing food is seen or 

 smelled. The stimulation of the salivary glands may also be 

 brought about by the thought of food that is liked, especially 

 when one is hungry. This is known as psychical or mental stimu- 

 lation. Flavoring substances and extractives that stimulate the 

 taste buds furnish chemical stimuli, and the pressure of food in 

 the mouth and the action of irritating substances cause a mechan- 

 ical stimulation. 



Saliva. Saliva consists of water, inorganic salts, some mucin, 

 and the enzyme ptyalin or salivary diastase. Saliva is usually 

 slightly alkaline in its reaction and has four distinct functions : 

 (1) it assists in mastication and swallowing by moistening and 

 softening the food ; (2) it lubricates the food and enables it to 

 slide smoothly down the esophagus ; (3) it dissolves dry and solid 

 food such as salt and sugar, thus enabling us to taste them, 

 and thereby stimulating a further flow of salivary and gastric 

 juices ; (4) the enzyme ptyalin acts upon starch, converting 

 it into sugars, dextrin and maltose. These are intermediate 



WH. FITZ. AD. EIO. — 9 



