ft 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.

[Illustration: =Diagram of the ear.=

_a_ outer ear.
_b_ drum head.
_c_ _d_ and _e_ bones to carry sound to inner ear.
_f_ _g_ and _h_ inner ear.
_i_ tube to the mouth.
_j_ middle ear.]

=174. Ear wax.=--Wax is formed just inside the ear. It keeps flies and
insects from crawling into the ear. Boys in swimming sometimes get
cold water into their ears. This may make them have an earache.