Percy: About the size of the fist of the person in whom it is found.
Amy: Then the baby’s heart is about as big as his dear little hand.
Mother: Can you describe its shape?
Helen: I think it is something like that of a pear or a strawberry, with the small end down.
The heart.
Mother: Here is a picture that will help us in learning its shape. I think I have not yet told you that the trunk of the body is divided into two large rooms. There is a partition running crosswise, called the di´a-phragm (di´a-fram). This gives us a large upper room, where we find the engine and bath room. The kitchen, eating room, store room, and waste rooms are in the lower part of the trunk, below the di´a-phragm. But we want to talk about the heart now. We have found about how large it is and what it is shaped like; let us next take a peep inside and learn, if we can, how it does its work.
Elmer: Didn’t you tell us once that the heart was made of muscles?
Mother: Yes; the outside walls are made of little strong muscles, and the inside is hollow. It is divided into four rooms. Each has its own name, but we will not try to learn them now. There is a wall reaching from top to bottom, and as it has no door, nothing can pass through from one side to the other. Then there are cross walls, or partitions, with folding doors in them, so there is an up-stairs and down-stairs room on each side. There are big pipes, or tubes, leading in or out from each room. They are called veins, or ar´ter-ies. The veins carry the blood to the heart, while the arteries carry it away.
Helen: But, mother, what makes the heart beat?