an not
expand, it will become useless. If your lungs can not take in air enough
to purify the blood, you can not be so well and strong as God intended,
and your life will be shortened.

If some one was sewing for you, you would not think of shutting her up
in a little place where she could not move her hands freely. The lungs
are breathing for you, and need room enough to do their work.

THE AIR.

The lungs breathe out the waste matter that they have taken from the
blood. This waste matter poisons the air. If we should close all the
doors and windows, and the fireplace or opening into the chimney, and
leave not even a crack by which the fresh air could come in, we would
die simply from staying in such a room. The lungs could not do their
work for the blood, and the blood could not do its work for the body.

Impure air-will poison you. You should not breathe it. If your head
aches, and you feel dull and sleepy from being in a close room, a run in
the fresh air will make you feel better.

The good, pure air makes your blood pure; and the blood then flows
quickly through your whole body and refreshes every part.

We must be careful not to stay in close rooms in the day-time, nor sleep
in close rooms at night. We must not keep out the fresh air that our
bodies so much need.

It is better to breathe through the nose than through the mouth. You can
soon learn to do so, if you try to keep your mouth shut when walking or
running.

If you keep the mouth shut and breathe through the nose, the little
hairs on the inside of the nose will catch the dust or other impurities
that are floating in the air, and so save their going to the lungs. You
will get out of breath less quickly when running if you keep your mouth
shut.

DOES ALCOHOL DO ANY HARM TO THE LUNGS?

The little air-cells of the lungs have very delicate muscular (m[)u]s'ku
lar) walls. Every time we breathe, these walls have to move. The muscles
of the chest must also move, as you can all notice in yourselves, as you
breathe.

All this muscular work, as well as that of the stomach and heart, is
directed by the nerves.

You have learned already what alcohol will do to muscles and nerves, so
you are ready to answer for stomach, for heart, and for lungs. Is
alcohol a help to them?

REVIEW QUESTIONS.

1. Besides carrying food all over the body, what
other work does the blood do?

2. Why does the blood in the veins look blu