THE MOUTH 



351 



material they want from the blood. They then give off 

 this material to the gland pockets, and from the pockets 

 it is poured out into the organ for which it was intended. 

 A gland separating a liquid from the blood is said to 

 secrete the liquid, and the liquid is called a secretion. 

 The glands that secrete the digestive juice of the mouth 

 are called salivary glands, and the 

 secretion is saliva. The gastric 

 glands secrete gastric juice for the 

 stomach. 



FIG. 278. 



Diagram of a Simple and a 

 Complex Gland. 



359. The Mouth. At the begin- 

 ning of the digestive tract is the 

 mouth. It contains the nerves of 

 taste, while just above it, in the nose, 

 are the nerves of smell. These two 

 senses therefore pass upon the quality 

 of the food at once. In the mouth 

 the food is broken up into bits 

 (chewed, or masticated) by the teeth. During chewing, 

 the glands of the mouth secrete saliva; the mouth 

 1 ' waters." They often secrete it before food gets into the 

 mouth; the odor or thought of food is enough to put them 

 into action. The tongue rolls the food about in the 

 mouth, so that the teeth may chew it again and again. 

 Finally, when we wish to swallow the food, the tongue 

 pushes it back to the opening of the throat, or pharynx. 



Saliva consists chiefly of water; this moistens the food 

 thoroughly before swallowing takes place. Some of the 

 solution of the food also gets to the nerves of taste. The 

 saliva is, however, more than water: it has an alkaline 



