In passing downward the food meets with five different digestive fluids: the saliva in the mouth; the gastric juice in the stomach; and the bile, pancreatic, and intestinal juices in the small intestine. Each digestive fluid acts only on some particular kinds of food. This action of the digestive fluids on food is called the chemical part of digestion. =The Care of the Mouth and Teeth.=—It is of the first importance that the mouth should be kept clean and as nearly aseptic as possible, for as the food is rolled about in the mouth by the process of mastication it is obvious that it will carry all the germs and mucus with it into the stomach. A nasal spray containing some solution of an alkaline or antiseptic nature should form an essential part of the toilet of the mouth. _The Teeth._—From simply an esthetic point of view well-kept teeth are beautiful and greatly enhance the charm of the face. But the proper care of the teeth is also essential to good digestion and good health. In perhaps the majority of people the teeth are sufficiently far apart for small particles of food to become lodged between them. If not promptly removed, the heat and moisture of the mouth, acting on these small particles, cause their decomposition and set up acid fermentation in the mouth; and it is this acid which causes the decay of the enamel and finally of the teeth. The decayed tooth gives still further lodgment to particles of food, and these, left to decompose, give rise to the most offensive gases, giving fetor to the breath, poisons the blood, and so injures the digestive and nervous systems. Where possible a tooth-pick and dental floss should be used immediately after each meal; the waxed dental floss between the teeth, and the flat end of the tooth-pick to remove any particles that may have worked in about the roots of the teeth and gums. A tooth-brush with good tooth-powder should be used twice a day. The brush should not be too broad, and is better if slightly curved. The bristles should not be too hard. The use of tooth-powder, which must be very fine, or tooth-paste is needed to produce sufficient friction to clean the teeth well. Warm water is a better solvent than cold, and, therefore, it is well to use it for cleansing the teeth. While it is generally known that decay if neglected will destroy a tooth, it is not so well known that many teeth are lost as the result of the accumulation of tartar at the gum margin. There is a great tendency to this, especially about the necks of the lower incisors and upon the teeth that are not used in chewing. The deposit of tartar encroaches upon the neck of the tooth and presses upon the gum; the latter becomes irritated or inflamed, and recedes from the tooth; malnutrition and loosening of the tooth follows. With very imperfect or decayed teeth proper mastication is impossible.