6o 



APPLIED PHYSIOLOGY 



78. Use of the water in saliva. The water of the saliva has 

 very important uses. The nerves of taste are covered by the epithelium 

 of the mucous membrane, and some of the food must be carried through 

 this epithelium to the nerves in order that it may be tasted. The water 

 of the saliva dissolves the food and soaks through the epithelium, 

 carrying a tiny amount of food to the nerves, and thus makes the sense 

 of taste possible. 



During digestion, food must be reduced to a fluid condition as thin 

 as milk. The saliva begins the process. Enough saliva is mixed with 



food to form a pasty mass which the 

 thin walled stomach can handle with 

 ease. 



79. Production of saliva. 



Saliva enters the mouth continu- 

 ally, but between meals only 

 about an ounce an hour is pro- 

 duced, while during a meal the 

 food increases in weight about 

 one half by the addition of saliva. 

 From one to three pints are pro- 

 duced daily. The flow of saliva 

 is excited by the act of chew- 

 ing, and by anything held in 

 the mouth, especially if it be of an agreeable taste and 

 odor. Hunger, or the sight or thought of agreeable food, 

 "makes the mouth water." The longer food is chewed 

 the more saliva is produced. This mixing and dissolving 

 action of the saliva is greatly aided by the movements of 

 the various parts of the mouth. 



80. Mastication. A morsel of food is pushed between the 

 molar teeth, which crush and grind it by the three movements of the 

 lower jaw. Between each movement of the jaw, the tongue and cheeks 

 roll the morsel into a firm mass so that the teeth can act upon it to 

 better advantage. The tongue has a delicate sensibility for the proper 

 condition and position of the food, and its varied and precise move- 



A salivary gland ( X 200) . 



tube of epithelium forming the 

 gland, cut lengthwise. 



b tubes cut crosswise. 



C connective tissue binding the 

 tubes in place. 



