I have told you, in Part First, how every thing in a plant or tree is made from the sap. This is, then, the building material, as we may say, of the plant. Now every thing in your body is made from the blood. The blood, then, is to your body what sap is to a plant. It is the common building material of the body.
You remember what I told you in Part First about the full-blown rose. This is made from the sap that comes to the bud through the pipes in the stem. Just so the little finger of the child becomes the large finger of the man, from the blood that comes to it through the pipes in the arm. And as the stem of the plant grows larger all the time, so does the arm of a child. The sap makes the stem grow, and the blood makes the arm grow.
If you cut off a branch of a plant it stops growing, because the sap does not come to it any longer. It soon dies and decays. So, if the arm of a child be cut off, it can not grow, because no more blood can come to it. Like the cut-off branch, it dies and decays.
The twig and the infant.
You see a twig come up out of the ground. It grows larger and larger every year. Soon it is a small tree. After many years it becomes very large, and spreads out its long branches over a great space. As you look up into it, you think of all that you see, its branches and leaves, as having been made from the sap that is continually running in its pipes. Now, as the little twig becomes a tree, so the infant in the cradle becomes the large man. And when you look up at a man, you can think of all his body as having been made from the blood that runs every where in its pipes, just as you think of a tree as made from the sap.
It is wonderful, as you have seen in Part First, how many and how different things are sometimes made from the same sap. Look at an apple-tree. There are the hard wood, the rough bark, the tender leaves, the beautiful blossoms, and the pleasant fruit, all made from the same sap. But the variety of things made from your blood is much more wonderful.
Variety of the things made from the blood.
Look at some of the things that are made from the blood. See the skin, the hair, the nails. Look at the soft red gums and the hard white teeth in the mouth. Then look at the eye. See the eyelids, the eyelashes, the firm, pearly-white coat of the eyeball, and the clear window in the front part of the eye. See, too, inside of this window, that round, colored curtain, with an opening in the middle that we call the pupil.
Bones, muscles, lungs, brain, nerves, bile, tears, etc., made from the blood.
All these different things that you see are made from the same blood. Then there are many other things inside of the body that you can not see. These are the hard bones, the red muscles, the white, shining cords by which the muscles pull the bones, the light, spongy lungs, the thick and firm liver, the soft brain, the white nerves, etc., etc.