=Digestion in the Mouth.=--_Saliva_ is formed by six glands: one in the cheek in front of each ear, one at the angle of each lower jaw, and one pair is beneath the tongue. Each gland opens into the mouth by a duct. Saliva is ropy because it is mixed with mucus formed by the mucous membrane lining the mouth; it usually contains air bubbles. There is a ferment in the saliva called _ptyalin_, which has the power of changing starch to malt sugar. If a bit of bread is chewed for a long time, it becomes sweet, because some of the _starch is changed to sugar_. The flow of saliva is caused by chewing, or by the sight, or even the thought, of agreeable food. Dryness of food is by far more powerful than anything else in causing the saliva to flow. Saliva is secreted only one fourth as fast when eating oatmeal and milk as when eating dry toast (Fig. 94). [Illustration: FIG. 94.--CELLS OF A SALIVARY GLAND _A_, after rest, full of granules; _B_, after short activity; _C_, after prolonged activity, cells shriveled and granules lost.] Starchy grains and fruits were eaten by early man without cooking, and required more chewing than sweet, ripe fruits or oils or proteids. Hence the saliva was given the power of acting upon the starch, for it must remain in the mouth longer. The saliva is alkaline; and if the food is not thoroughly mixed with it, the stomach digestion will also be imperfect, for the _alkaline saliva is necessary to excite an abundant flow of gastric juice in the stomach_ (Exp. 1). =Eating slowly= is difficult because of the grinding and cooking of food; hence the common practice of overeating. To eat slowly (1) do not take large mouthfuls; (2) do not take a second morsel until the first has been swallowed; (3) sit erect or lean back after putting food into the mouth; (4) the hands should lie idle most of the time. To lean forward and keep food traveling to the mouth like coal into a chute means overeating with all its bad effects. _Chewing gum_ is a coarse and impolite habit, and wastes the saliva, besides weakening the glands and irritating the stomach by the saliva that is continually swallowed. _Chewing tobacco_ has several of these disadvantages, besides allowing the poison in the tobacco to be absorbed by the mucous lining of the mouth. =The pharynx= (far′inks), =or throat=, is a muscular bag suspended behind the nose and mouth. (See Fig. 89, also Fig. 83.) There are _seven openings_ into the pharynx: two from the nostrils, two from the ears, one each from the mouth, larynx, and gullet. Which of these openings are downward? Forward? Lateral?