Sometimes a little dirt gets under the lids. Then the eye smarts or itches, and we want to rub it; but this may grind the dirt in deeper. Then you should get some one else to lift your eyelid and pick out the dust with a soft handkerchief. If you cannot get help, lift the lid by the eyelashes; blow your nose hard, and the tears may wash the dirt away.
Dust and disease germs may get into our eyes and make them sore and red. You should bathe your eyes well every time you wash your face. You should use a clean towel, for a dirty one may carry disease germs to your eyes. Some forms of sore eyes are catching. If any one has sore eyes, no one else should use his towels or handkerchiefs.
167. Tears.—Clear salt water is always running over the eyes and down a tube into the nose. The use of this water is to bathe the eyes and keep them clean. It sometimes runs over the lids in drops called tears.
168. How to use the eyes.—If using your eyes makes them painful or gives you a headache, you are straining your eyes. Facing a bright light strains the eyes. Shade your eyes while you study. A cap may be used as a shade if you cannot get anything else. Never try to look at the sun or a very bright light. You should have the light at one side or behind you. The light should be steady. Reading in a dim light will harm the eyes.
169. Near sight.—If you cannot read without holding your book less than a foot from your eyes, you are nearsighted, and should wear glasses all the time. If you do this, your eyes may be strong, and you may be able to see well.
170. Far sight.—If you cannot read without holding your book at arm's length, you are farsighted and need glasses. Most old persons are farsighted.
171. Alcohol and the eyes.—Alcohol makes the eyes red. It weakens the eyes and may produce blindness. A drunken person often sees double.
172. Tobacco causes dimness of sight and sometimes produces blindness.
173. Hearing.—We hear with the ears. Sound is made by waves in the air. The part of the ear on the outside of the head catches the air waves and throws them inside the ear. These air waves strike against a little drum. Three little bones then carry the waves on to nerves farther inside the head. Animals can turn their ears and catch sound from any direction.