When a child breathes through his mouth all the time, his face takes on a peculiar shape. His upper lip grows long, his lower jaw drops back, and his whole face looks flat. His voice has a peculiar sound, and he finds it very hard to keep up in his classes at school. Children with adenoids and large tonsils are always backward in their school work, and may become deaf if the adenoids and tonsils are not removed. If you breathe through your mouth instead of through the nose, go to the doctor and let him see if you have adenoids or large tonsils; if you have, let him take them out. You cannot possibly grow into a strong, healthy man or woman if you have adenoids and do not have them removed. =Questions.= 1. What does the body take out of the air? 2. What does the body put into the air? 3. What effect does impure air have on the body? 4. Why should one sleep with windows open? 5. What causes the unpleasant odor in a crowded room? 6. How would workmen benefit by properly ventilated workshops? 7. Name the helpful ways in which the air is changed while passing through the nose. 8. Why do some children breathe through the mouth? 9. What effect comes from mouth-breathing? =Remember.= 1. Impure air destroys health. 2. Never sleep in a room where the window is closed. 3. Avoid going into public places or workshops that are not well ventilated. 4. Air must pass through the nose before it is fit for the lungs. 5. Mouth-breathing is not natural and is usually due to some defect that can easily be cured. CHAPTER XII REST ESSENTIAL TO HEALTH [Sidenote: Why exercise is necessary] Exercise is necessary to make our bodies grow and become strong. If we stayed in bed all the time, our muscles would not grow and we could not even walk. If we did not exercise them, the cells in our brains would not grow and we should not know anything. Every part of our body must have exercise, that is, each part must do some work every day. If we used only one part of the body and did not give the other parts any work to do, only the part that we used would grow, while all the rest of the body would be small and weak. [Sidenote: Proportion of rest required] While every part should do some work each day, the whole body needs also to have a proper amount of rest. Even the heart, which seems to be working all the time, must rest. It rests between each beat. The muscles with which we breathe rest between each breath. Every person must have a certain amount of rest each day. A man should have at least eight hours' sleep in every twenty-four hours; boys and girls should have from nine to ten hours' sleep in every twenty-four. It is only while we are sleeping that we have complete rest. [Sidenote: Effect of overwork]