=Injury to the Nerves.=--The nerves are so important for the welfare of the body that all the chief ones are placed deep in the flesh, where they are not likely to be hurt. If the nerves leading to the arm were cut, it could not be moved, and we should have no feeling in it. The hurting of a part of the brain, the spinal cord, or the nerves may cause loss of feeling or motion in the leg, arm, or other part of the body. Such a part then seems asleep or dead and is said to have _paralysis_. Pressing on a nerve prevents it from acting. Sitting so as to press on the nerve of the leg often makes the foot go to sleep. The bursting of a blood vessel in the brain may let a blood clot form and press on the nerves which govern the arm or the leg. This pressure may cause paralysis. =Resting the Brain.=--When there is no food in the stomach, it has time to rest. When we sit down or lie down, the muscles get rest. The brain is always busy except when we are asleep. No one can live even a week without sleep. If a dog is kept awake five days, it will die. [Illustration: FIG. 89.--Sleeping in the position shown in the lower figure prevents free breathing and tends to cause round shoulders. The upper figure shows correct position.] Children need much more sleep than older persons. Men and women who work should have about eight hours of sleep daily to remain in good health. Children of twelve years should sleep nine hours each day; those of ten years, ten hours; those of seven years, eleven hours; and those of four years, twelve hours. =Getting the most out of Sleep.=--You should go to bed every night at about the same hour. This will help you to fall asleep as soon as you are in bed. Do not sleep in the clothes which you have worn during the day, but hang them up to air, and put on a night robe. Children should use a very low pillow, so that the body can lie straight in the bed. This gives the lungs and heart freedom to act. Do not lie on the back as this causes some of the organs to press on certain nerves and makes you dream. The windows should be opened wide because fresh air is the best aid to rest and health and keeps away tuberculosis. PRACTICAL QUESTIONS 1. What makes the parts of the body work together? 2. Describe the surface of the brain. 3. Name the three parts of the brain. 4. Of what is the outer layer of the brain made? 5. Where is the spinal cord? 6. What are nerve fibers? 7. What work does the brain do? 8. What makes the mind good or bad? 9. What is habit? 10. How long should children sleep? 11. How can you get the most good out of sleep? CHAPTER XXI HOW NARCOTICS AND STIMULANTS AFFECT THE BRAIN AND NERVES =What Narcotics and Stimulants Are.=--A _narcotic_ is something which when taken into the body makes the organs do their work more slowly and tends to cause sleepiness. Alcoholic drinks, tobacco, opium, soothing sirups, and pain killers are narcotics.