First Book in Physiology and Hygiene

by John Harvey Kellogg

3. The Venus's fly-trap has a very simple way of digesting its food. Its remarkable little trap serves it as a mouth to catch and hold its food, and as a stomach to digest it. The arrangement by which our food is digested is much less simple than this. Let us study the different parts by which this wonderful work is done.

4. The Digestive Tube.—The most important part of the work of digesting our food is done in a long tube within the body, called the digestive tube or canal.

5. This tube is twenty-five or thirty feet long in a full-grown man; but it is so coiled up and folded away that it occupies but little space. It begins at the mouth, and ends at the lower part of the trunk. The greater part of it is coiled up in the abdomen.

6. The Mouth.—The space between the upper and the lower jaw is called the mouth. The lips form the front part and the cheeks the sides. At the back part are three openings. One, the upper, leads into the nose. There are two lower openings. One of these leads into the stomach, and the other leads to the lungs. The back part of the mouth joins the two tubes which lead from the mouth to the lungs and the stomach, and is called the throat. The mouth contains the tongue and the teeth.

THE TEETH.

7. The Teeth.—The first teeth, those which come when we are small children, are called temporary or milk teeth. We lose these teeth as the jaws get larger and the second or permanent teeth take their place. There are twenty teeth in the first set, and thirty-two in the second. Very old persons sometimes have a third set of teeth.

SALIVARY GLANDS.

8. The Salivary (sal´-i-vary) Glands.—There are three pairs of salivary glands. They form a fluid called the saliva (sa-li´-va). It is this fluid which moistens the mouth at all times. When we eat or taste something which we like, the salivary glands make so much saliva that we sometimes say the mouth waters. One pair of the salivary glands is at the back part of the lower jaw, in front of the ears. The other two pairs of glands are placed at the under side of the mouth. The saliva produced by the salivary glands is sent into the mouth through little tubes called ducts.