[Ill.u.s.tration: FIG. 27.--The organs which get the food ready to enter the blood.]

[Ill.u.s.tration: FIG. 28.--Showing how the food in the dog is carried from the intestine to the liver and heart. The white tubes carry the fats up to the vein in the neck, and the dark tubes which are veins carry the other part of the food to the liver.]

=How Food gets into the Blood.=--An hour or two after food has entered the intestine it is almost as thin a fluid as milk. Millions of tiny fingerlike growths stick out from the inner side of the intestines and drink in the watery food. These little fingers for drinking up the food are scarcely one fourth as large as the point of a pencil. They are called _villi_.

The villi are filled with blood tubes having thin walls. The food pa.s.ses through these walls into the blood stream. Much of it then goes to the liver, but the fatty parts flow up a tube along the backbone and empty into a blood tube in the neck. From the neck and the liver the food goes with the blood to the heart which sends it to all parts of the body.

=What the Liver does.=--The liver is a dark red body nearly as large as the upper half of your head. It lies just below the diaphragm. It works night and day helping to keep the inner parts of the body clean and at the same time deal out food.

The liver takes some waste out of the blood and sends it out into the intestine with the bile. When there is no food in the intestine, the bile is stored up in the _gall bladder_ under the liver. The liver changes certain waste matter in the blood into such form that other organs can cast it out of the body. It also stores up certain parts of the food coming from the intestines and gives it out to the body little by little as it is needed.

=When and How much to Eat.=--When the food organs do not do their work rightly, the whole body becomes sick. Eating too much overworks the stomach. It becomes so full that the food cannot be moved about and well mixed with the juices. Germs then work on the food and make it sour. In fact the germs may change part of the food into a poison.

This poison will cause headache and a bad feeling.

Do not form a habit of taking powders to cure headache. They are likely to hurt the heart. Take less food, eat it more slowly, and do not wash it down with drink. Stop eating before your stomach feels full.

Each meal gives the stomach about four hours of work to do. It then needs one hour of rest. This shows that the time from one meal to the next should be about five hours. Very young children and sick persons need food oftener. Boys and girls should not eat candies, cake, or other food between meals. It spoils the appet.i.te and is likely to get the stomach out of working order.

=Danger Signals.=--A white or yellowish coat on the tongue, a bad breath, pain in the bowels, or a headache is a danger signal. It tells that the food organs are not doing their work as they should and unless help is given sickness is likely to occur. Medicine may help, but using foods easy to digest, eating less, chewing more, and getting plenty of exercise in the fresh air are likely to be the greatest aids to health.

=The Chewing of Tobacco and Digestion.=--Some men chew tobacco as much as ten hours every day. The taste of the tobacco makes the saliva flow from the glands into the mouth. This dissolves the poison out of the tobacco and it is then spit out. If the tobacco-soaked saliva were all swallowed, the man would be poisoned.

The chewing of tobacco causes the loss of much saliva which is needed to help digest the food. Anyone who tires his jaw by chewing tobacco is not likely to chew his food well. Some of the poison in the tobacco is taken into the body through the blood vessels in the lining of the mouth. This is shown by the fact that a boy not used to tobacco becomes very sick after he has chewed a mouthful for only ten minutes.

=Smoking and Digestion.=--Some persons think that the smoking of a cigar after a meal helps digestion. It may do so in some cases. If a lawyer is much excited about a case he is trying, or a business man is in trouble about his losses, the thinking causes the blood to flow to the head when it is needed in the stomach to give out digestive juices.

The taste of the tobacco smoke may cause some gastric juice to run out into the stomach, but at the same time it is likely to hurt the nerves of taste so that food cannot give so much enjoyment as when the nerves are unharmed. Although smoking may at the time help digestion a little, the poison in the tobacco may afterward injure the body. This poison is especially harmful to growing bodies, and boys who are wise will refuse to smoke on all occasions.

=Beer and Digestion.=--Some people drink beer with their meals because they think it makes the food taste better. It really prevents them from getting the full taste of the food because they wash it down before it is well soaked with the saliva.

[Ill.u.s.tration: FIG. 29.--The stomach, showing the arrangement of the muscular fibers which alcohol may hinder from doing good work. At the right a piece is cut out of the top layer of muscle.]

The flavor of beer may sometimes cause an extra flow of gastric juice into the stomach, but the alcohol in the beer is likely to make the movements of the stomach slower. This prevents the food from being well and quickly mixed with the juices. Several gla.s.ses of beer used at one meal will make the stomach do its work very slowly, and it will not do it well.

=Wine and Digestion.=--Wine is taken by some people to give more appet.i.te for food. It is likely, however, to do more harm than good because the alcohol in it makes the muscles which mix the food in the stomach act more slowly. Some of the food may sour before it gets wet with the juice. Much wine used at a meal is always harmful.

=Natural Appet.i.te.=--If one is in health, he should feel a desire for his food at every meal. This desire for a reasonable amount of food is a natural appet.i.te. Fresh air and exercise will do much to give one the right kind of an appet.i.te. The eating of much sweets and the breathing of bad air are likely to spoil the appet.i.te.

The use of some things, such as opium, tobacco, beer, wine, and whisky, creates an unnatural appet.i.te. That is, after one has used these articles a few months he cannot stop their use without great suffering. The younger the person, the sooner the appet.i.te becomes fixed. For this reason _young persons should never use tobacco or alcoholic drinks of any kind_.

PRACTICAL QUESTIONS

1. What is digestion?

2. Name the parts of the food tube.

3. Where does saliva come from?

4. Explain how the food is acted on in the mouth.

5. Why should food be well chewed?

6. What forms the gastric juice?

7. Of what use is the gastric juice?

8. How long does food stay in the stomach?

9. Name some foods easily digested.

10. What does the intestine do?

11. What are villi?

12. Tell how the food gets into the blood.

13. Of what use is the liver?

14. Why should we not eat too much?

15. Should we eat between meals?

16. Give three reasons why you should not use tobacco.

CHAPTER VIII

THE CARE OF THE MOUTH

=Sickness often begins in the Mouth.=--A clean mouth and sound teeth have much to do in keeping one well. The germs which cause nearly a half million deaths in the United States every year enter the body through the mouth. If the mouth is unclean, only one or two disease germs entering it may remain there and grow.

[Ill.u.s.tration: FIG. 30.--The teeth of the upper jaw at eleven years of age.]

It is just as important to wash the mouth two or three times each day as it is to wash the hands and face. A few germs of diphtheria, sore throat, or tuberculosis are likely to get into the mouth any day, but if the mouth and teeth are well washed with a brush morning and night, the germs will not have time to grow and cause sickness.

=The Teeth.=--The first twenty teeth that appear are called the _milk set_. The eight front teeth grow out during the first year of life and back of these twelve others appear during the second year. Between the seventh and the tenth year all of the milk teeth are lost because others grow beneath them and push them out.

[Ill.u.s.tration: FIG. 31.--The full set of teeth on the right side at twelve years of age. The numbers show at what year of age each one grows out of the gum.]

The first four teeth of the second set appear in the sixth year, just behind the last milk teeth (Fig. 30). These teeth should be watched very closely and at the first sign of decay you should go to the dentist. As the milk teeth get loose and come out, the second set of teeth take their places.

If you are ten or eleven years old, you should have twelve good teeth in the upper jaw and the same number below. The last ones to break through the gums are the four wisdom teeth at the back of the mouth.

They appear after the seventeenth year.

The front teeth are called _incisors_ because they are used to cut the food. The back teeth are named _molars_ because they are used in grinding the food.