The discontented pendulum.
There is a pretty story, by Miss Jane Taylor, about a discontented pendulum. The pendulum of a clock in a farmer’s kitchen, in thinking over the ticking that it had got to do, became discouraged, and concluded to stop. The hands on the clock-face did not like this, and had a talk with the pendulum about it. The pendulum was, after a while, persuaded to begin its work again, because it saw, as the hands said, that it always had a moment to do every tick in. The pendulum’s foolish waste of time in complaining made the farmer’s clock an hour too slow in the morning.
Questions.—What is said about the circulation of the sap and the blood? What is said about the heart? What about the arteries? What are the capillaries? By what pipes does the blood come back to the heart? Where can you see some of the veins? Why are the arteries laid deeper than these veins? Why are they made stronger than veins? What is the color of the blood in the arteries? What is its color in the veins? Is the sap kept in motion in the same way that the blood is? What is said about the work that the heart does? Tell about the pendulum.
CHAPTER VIII.
BREATHING.
What do you breathe for? That is plain enough, you will say: I can not live without breathing. But why is it that your life depends on your breathing? This I will explain to you.
The blood changed from dark to red in the lungs.
You remember that I told you that the blood that comes back to the heart in the veins is dark; it is not good blood. It has been used while it was in the capillaries in building and repairing bone, and skin, and muscle, and nerve, etc. It is not fit to be used again so long as it is dark blood. What shall be done with it? It must be made in some way into good red blood again. Now the factory where this is done is the lungs.
Just as fast as the dark blood comes to the heart, it sends it to the lungs to be made into red blood, then it goes back to the heart to be sent all over the body. But how, you will ask, is the dark blood changed into good red blood in the lungs? It is done by the air that you breathe in; every time that you draw a breath, air goes down into the lungs and changes the blood that it finds there.
And now you see why it is that you have to breathe to keep alive. If the air does not go down into the lungs, the dark blood that is there is not changed into red blood: it goes back to the heart dark blood, and is sent all over the body; but this dark blood can not keep you alive: it is the red blood that does this.