[Illustration: _The lungs, heart, and air-passages._] 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?