Mother: I thought that would be about the first thing you would wish to know, and I will explain the best I can. When the muscles which make up the heart draw together, the rooms inside become small, and the blood in them is squeezed out. When the muscles slacken, the rooms become larger, and the blood rushes in and fills them again. So the blood keeps coming in and going out of the heart all the time, and it causes it to make the movement which we call beating.
Amy: How fast does it beat?
Mother: In very little children it beats from one hundred and twenty to one hundred and forty times a minute. In grown people it beats sixty or seventy times, and when the body-house has grown old and feeble, it beats slower still. Percy, you may run up and down stairs and then tell us if you see any difference in your heart-beats.
Percy: I believe they are twice as many as they were when I was sitting still.
Mother: Hardly as many as that, but the heart beats much more quickly. Can you think of anything else that makes the action of the heart faster?
Helen: When I was frightened this morning I could hear my heart go thump, thump, and I am sure it seemed to be in a hurry.
Mother: Yes; moving quickly, fright, anger, or joy makes this busy pump work more quickly. Sadness and grief cause it to work slowly. It beats faster when we are standing than when we sit still, and the motion is slower when we lie down than when we are sitting.
Elmer: Why did the doctor put his finger on my wrist when I was sick, mother?
Mother: He wanted to know how your heart was working, so he felt your pulse. Sometimes when people are ill it beats very, very fast, and sometimes it moves more slowly than it should.
Amy: What is the pulse?