MOTHER: Every building must have a foundation and a frame of some kind to make it strong and give it shape. It is the same with the house we call our body. The frames of houses which men build are made of wood or iron; but the framework of the body is built of bones. Perhaps you have noticed that in the frames of buildings some pieces of timber are short, and some are long, and they are cut into many different shapes and sizes. So it is with the bones of the body. How many do you think it takes to make our frame? [Illustration: Skeleton] HELEN: About fifty. PERCY: I guess one hundred. MOTHER: Not quite right, for there are over two hundred. All the bones together are called the skeleton. The frame of a house divides it into rooms, and on it are fastened the boards, laths, and shingles. In the house in which we live the flesh is fastened to the bones, and the whole is covered with skin. This framework also protects the curious rooms inside the trunk of the body. The largest bone in our frame is the leg bone, which reaches from the hip to the knee. It is called the _femur_, or thigh bone. ELMER: Are the bones solid, mother? MOTHER: No; I have brought some pictures to show you how they look, for we can not see our own bones. One of them shows a bone that is sawed through lengthwise. You see the larger part at the end is full of little holes, like a sponge. This makes it light and strong. There is a hollow place in long bones filled with marrow. It also fills the spongy parts. Marrow is made of fat and cells. [Illustration: _The thigh bone._] You must not think that live bones look like one which has been lying out-of-doors a long time. Live bones are full of blood and have a pinkish color. They also have an outside skin, which can be peeled off, as you see in this picture. [Illustration: _A bone with the outside skin partly peeled off._] AMY: What are the bones made of? [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.