=56. Habit.=--When men have used tobacco for some time, they like it and feel bad without it. So they get into the habit of using it, and find it hard to stop. The tobacco seems to help them, but it does not do so. It cheats men, and they do not know it. =57. Chewing gum.=--Chewing gum is made from pitch or paraffin, for these substances will not dissolve in the mouth. The gum is flavored with sugar and spices. The gum and its flavors are not harmful in themselves, and yet chewing them is harmful. Chewing makes a great deal of saliva flow. All this saliva is wasted, and when we eat our meals we may have too little. Then our food will not digest well, but we shall have dyspepsia and headaches. By pulling and handling the gum while chewing it, you may get some poisonous dirt into your mouth, and make yourself very sick. Even if your gum should not harm you, there is a good reason for letting it alone. When you are chewing gum, you look as if you were chewing tobacco. No one likes to see a boy or girl even appearing to chew tobacco. If you form a habit of chewing gum you will be more likely to chew tobacco when you are grown. WHAT WE HAVE LEARNED 1. Men use tobacco for the sake of its nicotine. Nicotine is a very strong poison. 2. Tobacco causes a man to waste his saliva. 3. Tobacco makes the mouth dry. 4. Tobacco hinders digestion. 5. Tobacco stains the teeth, and makes the breath smell bad. 6. Tobacco makes a person sick at the stomach. 7. Tobacco weakens the muscles. 8. Tobacco is more harmful to the young than to grown persons. 9. Chewing is the worst form of using tobacco. 10. Smoking cigarettes is the worst form of smoking. CHAPTER VII FERMENTATION =58. Souring of fruit.=--When a little fruit is set away in a warm place for a day or two it sours or ferments. Anything sweet will do the same thing. Little bubbles rise up through the juice and a foam comes on top. Then the juice has a sharp taste or is sour. Canned and preserved fruit becomes sour soon after the jar is opened, and cider soon turns to vinegar. All fruit juice does this even in cold weather. But in cold weather it keeps for a longer time. [Illustration: =Fermentation in a jar of cherries.=] =59. Preserving fruit.=--If your mother wishes to keep fruit all winter she boils it and at once puts it into tight jars. This shuts out the air and then the fruit keeps good all winter. Boiling kills all living things, and no more can get in through the tight jars. Does a living thing have anything to do with making the fruit juice turn sour?