THE DIGESTION 



207 



is excited by the act of chewing and by anything held 

 in the mouth, especially if it be of an agreeable taste or 

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

 makes the mouth water by stimulating the cells in the 

 glands to activity by means of the nerves. But by far 

 the most powerful of all the excitants to the salivary flow 

 is dryness of the food. Only one fourth as much saliva is 

 deposited in the same length of time when eating oatmeal 

 and milk as when eating crackers or dry toast (Fig. 164). 



B 



FIG. 164. Cells of the Salivary Gland. 



A t after rest; B, after a short period of activity; C, after a prolonged period of activity. 

 Shriveling and loss of granules occur. 



I. Absorption, or the passage of digested food into the 

 blood vessels, is an important sequel of the digestive pro- 

 cess. A little of the water containing sugar and salts is ab- 

 sorbed from the mouth directly into the blood vessels. 

 Poisonous substances may sometimes be absorbed from the 

 mouth in sufficient quantities to produce death. If a drop 

 or two of prussic acid be placed on the tongue or on the 

 mucous membrane, death occurs in a few minutes, 

 although not a particle of it has reached the stomach. 

 Boys who take their first chew of tobacco learn in a dis- 

 agreeable way that the entire body may be affected by 

 absorption from the mouth. The absorption in the mouth 

 is insignificant in amount compared to the absorption that 

 takes place in the small intestine. 



369. The Pharynx (far-inks), a muscular bag ODen- 

 ing from the nose and mouth, is four and a half inches 



