CHAPTER XV.
THE LUNGS.
HE 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.
The lungs, heart, and air-passages.