Percy: And how far does the blood go?
Mother: Perhaps it first takes a trip through the trunk of your body, down through your right leg, and on to the end of your big toe. The tubes at last become very small, and there are so many of them that they are like a network of the finest lace. A hair would seem like a big rope beside them. They are so very tiny that you can not see them. Their walls are thinner than tissue paper, and they are so close together that you can not touch your skin with the point of a needle without touching some of them. When the blood comes to these tiny tubes, it does not travel so fast as at first, and as it passes along, the muscles pick it to pieces, take the part they want as food, and load the blood down with waste which they can not use. When they are so hungry, the blood is glad to feed them and give them the oxygen, which makes them warm.
Amy: Did it stay long in those little tubes?
Mother: No; it went through as quickly as it could, and on its way back found itself in bigger tubes, which keep growing larger; for it is now on its way back to the heart. This picture will help you to see the road it travels. It is now a dark red color, and unfit to work longer till it is washed. Back it goes to the heart, the tubes through which it travels growing larger all the way until it tumbles into the right top room of the heart, which, as you have learned, always has dirty, worn-out blood in it. But it is not allowed to stay there; for between this room and the lower right room there are three folding doors kept in place like the two on the left side, and through them it passes. The walls of the rooms on the right side of the heart are not as thick as those on the left side. I think that must be because the left side sends the blood farther than the right.
Helen: Does the blood stop to rest in the lower right room?
Mother: Oh, no; it never rests as long as there is any life in it! The heart squeezes it out into another big tube, and it soon finds itself in the bath room, where it is washed through and through, and its color becomes as bright red as when new.
Amy: And where does the blood then go?
Mother: Straight back to the left side of the heart, where it is pumped out the same as before; and this time we will say it goes to the kitchen of the house you live in, and helps the cook get the dinner you have eaten ready to be made into more blood. The old blood eats some of the good things, and again it is sent to the right side of the heart and back through the bath room.
Percy: And what then?