THE blood flows all through the body, carrying good food to every part. It also gathers up from every part the worn-out matter that can no longer be used. By the time it is ready to be sent back by the veins, the blood is no longer pure and red. It is dull and bluish in color, because it is full of impurities.

If you look at the veins in your wrist, you will see that they look blue.

If all this bad blood goes back to the heart, will the heart have to pump out bad blood next time? No, for the heart has neighbors very near at hand, ready to change the bad blood to pure, red blood again.

THE LUNGS.

These neighbors are the lungs. They are in the chest on each side of the heart. When you breathe, their little air-cells swell out, or expand, to take in the air. Then they contract again, and the air passes out through your mouth or nose. The lungs must have plenty of fresh air, and plenty of room to work in.

If your clothes are too tight and the lungs do not have room to expand, they can not take in so much air as they should. Then the blood can not be made pure, and the whole body will suffer.

For every good breath of fresh air, the lungs take in, they send out one of impure air.

In this way, by taking out what is bad, they prepare the blood to go back to the heart pure and red, and to be pumped out through the body again.

How the lungs can use the fresh air for doing this good work, you can not yet understand. By and by, when you are older, you will learn more about it.

CARE OF THE LUNGS.

Do the lungs ever rest?

You never stop breathing, not even in the night. But if you watch your own breathing you will notice a little pause between the breaths. Each pause is a rest. But the lungs are very steady workers, both by night and by day. The least we can do for them, is to give them fresh air and plenty of room to work in.

You may say: “We can’t give them more room than they have. They are shut up in our chests.”

I have seen people who wore such tight clothes that their lungs did not have room to take a full breath. If any part of the lungs can 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 (mus’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 blue?

3. Where is the blood made pure and red again?

4. Where is it sent, from the lungs?

5. What must the lungs have in order to do this work?

6. When do the lungs rest?

7. Why should we not wear tight clothes?

8. How does the air in a room become spoiled?

9. How can we keep it fresh and pure?

10. How should we breathe?

11. Why is it better to breathe through the nose than through the mouth?

12. Why is alcohol not good for the lungs?