Our body is made of many parts. Its head thinks. Its legs carry it, and its arms and hands take hold of things. The leg cannot do the work of the arm, nor the head do the work of the hand; but each part does only its own work.

1. The simplest animal.—Some animals have parts like a man's; but these parts are fewer. No animal has arms or hands like a man. A fish has little fins in place of legs and arms, while a worm has not even a head, but only a body, and yet it moves. An oyster has only a body and cannot move. The simplest of all animals is very small. A thousand of them would not reach an inch. Yet each is a complete animal. It is called the ameba. It is only a lump of jelly. It can put out any part of its body like an arm and take a lump of food. This same arm can eat the food, too. It can also put out any part of its body like a leg and move by rolling the rest of its body into the leg. It can do some things better than a man can do them, for any part of its body can do all kinds of work. So the ameba grows and moves and does as it likes.

2. Cells.—A man's finger moves and grows something like a separate animal, but it must keep with the rest of the body. A little piece of a finger moves and grows, too. If you should look at a finger, or any other part of your body, through a microscope, you would see that it is composed of little lumps of jelly. Each little lump looks like an ameba. We call each lump a cell. The cells make up the finger.

3. What cells do.—Each cell acts much as an ameba does. From the blood it gets food and air and takes them in through any part of its body. It also grows and moves. But the cells are not free to do as they wish, for they are all tied together in armies by very fine strings. We call these strings connective tissue. One army of cells makes the skin, and other armies make the bones and flesh. Some armies make the fingers, and some the legs. Every part of our body is made up of armies of separate cells.

4. The mind.—The body is a home for the mind. The cells obey the mind. The mind pays the cells by feeding them and taking good care of them. When an army of cells is hurt, the body feels sick, and then the mind tells the whole body to rest until the cells are well again. When we study about a man's body, we learn about the separate cells in his body.

WHAT WE HAVE LEARNED