If then, our legs want to say: “We’re sitting on something hard and sharp, please may we move,” they call us up over the nerves. If they want to say: “We have been growing too fast, and it’s high time we stopped and gave something else a chance,” they do it by turning something into the blood. But if they want to say: “We’re so dead tired that we simply can’t walk another step,” then as you know, they use both methods—fatigue toxins and very dreadful aches.
XLIV
What Becomes Of The Tadpole’s Tail
The lymph cells, blood cells, white blood corpuscles, as they are variously called, are a sort of standing army, always on duty to repel invasion by any living germs of disease. In times of peace, however, when there is no enemy to be set upon and devoured, they have to work. All soldiers have to work when there is no fighting to be done; and sailors on a battle ship have to keep it clean and in order, row the captain about in his boat, and take turns paring potatoes for the cook. So the cells in our blood are in this like other fighting men.
Their particular work is to keep the body cleaned up, especially the blood. Besides this, they take down and cart away any tissue or organ or part of the body that is no longer any use.
There, for example, is the polywog’s tail, after he becomes a frog—also his gills. The polywog, of course, is pretty nearly a fish, with gills and tail, who breathes water. But Brer Frog is pretty nearly a land animal. He breathes with lungs, tho not to be sure especially good ones, so that he has to breathe thru his skin also to help out. At any rate, he has lost his fishy gills, and no longer has any tail.
Where has the tail gone? The white blood corpuscles have eaten it up; and with it, a lot of other things, gills among the number, which the tadpole has to have, but the frog has no use for.
The tadpole, as you know, has no legs. When they start growing (you can see them under the skin, almost the first sign of the coming change) these growing legs turn something into the blood which is a signal to the blood cells to get to work eating up the tail. So the blood cells do get to work. They devour the flesh, cutting into it much as certain insects gnaw into wood, or a woodchuck digs a hole in the ground. Then as fast as the blood cells take down the flesh that is no longer useful, it is used again to build up the new legs. So really the tadpole’s tail is used over to make the frog’s legs.
Much the same thing happens when a caterpillar turns to a butterfly. The caterpillar, as you have no doubt often seen, shuts himself up in a hard shell. Inside this coffin, or chrysalis, the body of the caterpillar is taken to pieces, and changed over into a sort of thick milk. Then out of this thick milk, the butterfly is formed.
