The saliva in the mouth helps to prepare the food, before it goes into the stomach. Tobacco makes the mouth very dry, and more saliva has to flow out to moisten it. But tobacco juice is mixed with the saliva, and that must not be swallowed. It must be spit out, and with it is sent the saliva that was needed to help prepare the food. Tobacco discolors the teeth, makes bad sores in the mouth, and often causes a disease of the throat. You can tell where some people have been, by the neatness and comfort they leave after them. You can tell where the tobacco-user has been, by the dirty floor, and street, and the air made unfit to breathe, because of the smoke and strong, bad smell of old tobacco from his pipe and cigar and from his breath and clothes. REVIEW QUESTIONS. 1. What are organs? 2. What work do the front teeth do? the back teeth? 3. What are the teeth made of? 4. What causes the toothache? 5. How is the enamel often broken? 6. Why should a tooth-pick be used? 7. Why should the teeth be well brushed? 8. When should they be brushed? 9. What bones form a case or box? 10. What is the upper room of this box called? the lower room? 11. What organs are in the chest? the abdomen? 12. What is the stomach? 13. What does its lining do? 14. What do the stomach and the gastric juice do to the food we have eaten? 15. How did anybody find out what the stomach could do? 16. Why must all the food we eat be changed? 17. Why do you need food? 18. Why do people who are not growing need food? 19. What does alcohol do to the gastric juice? to the stomach? 20. What is the use of the saliva? 21. How does the habit of spitting injure a person? 22. How does tobacco affect the teeth? the mouth? 23. How does the tobacco-user annoy other people? FOOTNOTE: [Footnote C: The food is partly prepared by the liver and some other organs.] CHAPTER XI. WHAT DOES THE BODY NEED FOR FOOD? [Illustration: N]OW that you know how the body is fed, you must next learn what to feed it with; and what each part needs to make it grow and to keep it strong and well. WATER. A large part of your body is made of water. So you need, of course, to drink water, and to have it used in preparing your food. Water comes from the clouds, and is stored up in cisterns or in springs in the ground. From these pipes are laid to lead the water to our houses. Sometimes, men dig down until they reach a spring, and so make a well from which they can pump the water, or dip it out with a bucket. Water that has been standing in lead pipes, may have some of the lead mixed with it. Such water would be very likely to poison you, if you drank it.