Mother: Yes; and this “going round and round,” as you say, is called the cir-cu-la´tion. This drop of blood would have kept going until it was used up in mending your body and helping keep it alive, if it had not slipped out through the cut in Amy’s finger into the world in which you live and move.
I know you have all enjoyed hearing how the blood travels through the body. Let me tell you a little story I read of what a boy said in school. His teacher asked him to tell the class how the blood cir´cu-lates, or goes round and round.
“Please, sir,” said the lad, “the blood goes down one leg and up the other.”
“Very clever of it, I am sure,” said the teacher. “How does it get across?”
Perhaps that was something the boy had not thought of, and I am sure you would never give such an answer as that since you have heard the story of a drop of blood. Let us see the cut finger where it came out.
Amy: It doesn’t bleed at all now, mother.
Mother: No; and that makes me think to tell you something else about this wonderful caretaker. If we had a quart of blood and should let it stand awhile, it would become thick like jelly. But if you should take a bundle of twigs and keep stirring it round and round, it would not get thick at all. If you looked at your bundle of twigs after stirring the blood with it, you would find the twigs covered with a sticky substance. If you should wash them, you would wash away the red color, and would have left a soft, stringy mass all matted together.
Helen: But what is it good for?
Mother: It is called fibrin, and if it were not in the blood, you would bleed to death if you cut yourself. So long as the blood stays in the body, the fibrin goes quietly with it wherever it goes; but if it begins to run away, as it did from Amy’s finger, the fibrin goes to work at once to cork up the place so it can not get out.
Percy: How long does it take the blood to go from the heart through the body and back again, mother?