[Illustration: _End of a bone sawed open._]
MOTHER: Of animal and earthy matter. You can take the animal matter out of a bone by burning it in the fire. It will then be white and brittle. If you soak a bone in a kind of acid, the earthy matter will come out, and it will then be so soft you can tie it in a knot like this. When children are very young, their bones are soft and easily bent. This is because there is more animal than earthy matter. Children sometimes get hard falls, and their bones bend but do not break. Some, when very young, have legs that are bent like a bow. This is caused by standing and walking before the bones are strong enough to bear the weight of the body, or by disease.
[Illustration: _A bone tied in a knot, after the earthy matter has been removed by an acid._]
In very old people the bones contain more earthy matter, and they break easily. Grand´fa-ther and grand´moth-er must be careful not to fall, for if they break a bone it will take a long time to heal.
When we take a baby, we should not lift him by his arms, and we must hold him so his bones will not grow out of shape. As he grows older, enough earthy matter will go into his bones to make them hard and strong.
PERCY: But you said there was lime in the bones, mother.
MOTHER: Yes, the earthy matter is partly lime. The blood goes into the bones through tiny blood-vessels, and at all times of day and night the bones keep eating their breakfasts, dinners, and suppers of lime, which they find in the blood.
[Illustration: “_We should not lift him by his arms._”]
HELEN: What kind of food is best for the bones?
MOTHER: Good whole-wheat bread will furnish them all they need. Peas and beans are also good.
We will now look at the largest bones of our body frame, and see if we can learn something of their size and shape. We will not try to learn their hard names now, but will leave that till we are older.
We will begin with the bones of the head. They form what is called the skull. It is made of a number of bones, joined like two saws with the teeth hooked together. The “chin bone,” or jaw bone, is one of the bones of the head.
Let me show you a picture of one of the most wonderful bones of the body. It is called the _spine_, or spinal column. Perhaps you can feel some little knobs or ridges in your back. The back-bone is made of twenty-four little bones piled one on top of another. Suppose you had twenty-four spools or reels of cotton, and you should run a string through them. When you hold them upright, you see you can bend them any way you wish, or keep them straight. Now if each spool had three wings like the one in the picture, they would be shaped very much like the bones that form the spine. The string is like the marrow, or “spinal cord,” which passes through the spinal column from top to bottom. The bones which make up the lower part of the spine are much larger than those at the top. Little soft cushions are placed between all these bones, something like India-rubber. These cushions are to keep the body and brain from being jarred, just as the springs in our carriage help you to ride easily. They also help us to bend the body backward or forward as we choose. You see if the spine was one long straight bone we could not bend at all. If we keep bending over while walking or working, after a time the cushions will get used to that position and we shall have a bad figure.