MOTHER: So it would if it was not made new by the food you eat. It keeps taking as well as giving as it goes round and round through the body. You would not expect a housekeeper to keep everything tidy and clean in a house, and not give her what she needed to make her strong and able to work; and so the master of the house gives the blood plenty to eat; and it makes no complaint as long as it can do its work well. It is a very busy person, we might say, and, as there is no end of things to do in the house in which you live, the blood works night and day. ELMER: But I don’t see how the blood can take with it all that is needed to mend the different parts of the house. MOTHER: It is supposed to carry with it a supply of everything that is needed to keep the house in order as it goes, so that when a bone says, “I want some lime,” or a muscle says, “Please give me some al-bu´men,” each part gets what it calls for if it is in the blood. Whether it has what every part needs depends on what the master of the house sends into the kitchen to make blood. Have I told you about the filters in the body? AMY: I’m sure you have not. Please tell us now. MOTHER: There are two of them in the lower part of the trunk close to the back, one on each side. They are the shape of a bean, and are called the kidneys. The blood passes through them, and some of the poisons it has picked up are strained out and sent to a storeroom, called the bladder, where they are kept till the brain gives an order to send them away. HELEN: But there is one thing I would like to know. I can see how blood can run down-hill into our fingers and toes, but I can’t see how it can climb back up to the heart again. Will you please tell me? [Illustration: _A kidney._] MOTHER: The heart is the power that sends it through the arteries to every part of the body, whether it is up-hill or down. Now when the blood has come to the end of its journey, and has reached the tiny hair-like veins of which I told you, more blood keeps coming down and pushes it on till it starts back through the larger veins. The blood keeps crowding behind, and the veins are made in such a way as to help it climb up. PERCY: But how are they different from the arteries? MOTHER: Did you ever see little watch-pockets hung in bedrooms in which to put watches? Well, the veins have tiny pockets in them, as you see in the picture. [Illustration: “_Veins have tiny pockets in them._”] AMY: But I don’t see how that helps the blood in climbing.