187. Shape of muscles.—Bones are covered with muscles. Muscles give shape to the body, and move it about. One half of the body consists of muscles. These are arranged in bundles, and each causes a bone to make one motion. There are over four hundred separate bundles of muscle in the body.

One end of a muscle is large and round and is fast to a bone. The other end tapers to a strong string or tendon. The tendon passes over a joint, and becomes fast to another bone. You can easily feel the tendons in the wrist and behind the knee.

A muscle is made of tiny strings. You can pick them apart until they are too fine to be seen with the eye. Each string is a living muscle cell. It is the largest kind of cell in the body. You can see the fine strings in cooked meat.

188. How muscles act.—A nerve runs from the brain, and touches every cell of the muscle. When we wish to move, the brain sends an order down the nerve. Then each muscle cell makes itself thicker and shorter. This pulls its ends together, and bends the joint. We can make muscle cells move when we wish to, but we cannot make any other kind of cell move. We make all our movements by means of our muscles.

189. Where you can see muscles.—In a butcher's shop you can see lean meat. This is the animal's muscle. White and tough flesh divides the tender red meat into bundles. Each red bundle is a muscle. You will see how the muscle tapers to a string or tendon. The butcher often hangs up the meat by the tendons. You can see the muscles and tendons in a chicken's leg or wing when it is being dressed for dinner.

Roll up your sleeve to see your own muscles. Shut your hand tight. You will see little rolls under your skin, just below the elbow. Each roll is a muscle. You can feel them get hard when you shut your hand. You can feel their tendons as they cross the wrist.

Open your hand wide. You can see and feel the tendons of the fingers upon the back of the hand. These tendons come from muscles on the back of the arm. You can feel the bundles of these muscles when they open the fingers. There are no muscles in the fingers, but all are in the hand or arm. You cannot open your hand so strongly as you can close it.

190. Strength of muscle.—By using a muscle you can make it grow larger and stronger. If you do not use your muscles they will be small and weak. Children ought to use their muscles in some way, but if they use them too much, they will be tired out. Then they will grow weaker instead of stronger. Lifting heavy weights, or running long distances, tires out the muscles, and makes them weaker. Small boys sometimes try to lift as much as the big boys. This may do their muscles great harm.

191. Round shoulders.—The muscles hold up the back and head, and keep us straight when we sit or stand. A lazy boy will not use his muscles to hold himself up, but will lean against something. He will let his shoulders fall, and will sit down in a heap. Sometimes he is made to wear shoulder braces to keep his shoulders back. This gives the muscles nothing to do, and so they grow weaker than ever. The best thing to do for round shoulders is to make the boy sit and stand straight, like a soldier. Then he will use his muscles until they are strong enough to hold his shoulders back.

192. How exercise makes the body healthy.—When you use your muscles, you become warmer. Your face will be red, for the heart sends more blood to the working muscle cells. You will be short of breath, for the cells need more air. You will eat more, for your food is used up. Your muscles are like an engine. They get their power from burning food in their own cells. When they work they need to use more food and air. So working a muscle makes us eat more and breathe deeper. The blood flows faster, and we feel better all over. The muscle itself grows much larger and stronger.

If we sit still all day, the fires in our bodies burn low and get clogged with ashes. We feel dull and sleepy. If we run about for a few minutes, we shall breathe deeply. The fires will burn brighter. Our brains will be clearer, and we shall feel like work again. Boys and girls need to use their muscles when they go to school. Games and play will make you get your lessons sooner. 193. How to use the muscles.—You should use your muscles to make yourself healthy, and not for the sake of growing strong. Some very strong men are not well, and some men with small muscles are very healthy. Some boys have strong muscles because their fathers had strong muscles before them. Strength of muscle does not make a man.

You ought to have healthy muscles. Then your whole bodies will be healthy, and you can do a great deal of work. You ought to learn how to use your muscles rather than how to make them strong. An awkward and bashful boy may be very strong, but he cannot use his muscles. A boy is graceful because he can use them.

The best way to use your muscles is in doing something useful. You can help your mother in the house and your father at the barn. You can run errands. You can learn to use carpenter's tools or to plant a garden. Then you will get exercise and not know it. You will also be learning something useful.

Play is also needed. Work gets tiresome, and you will not want to use your muscles. Play is bad when it takes you from your work or when you hurt yourself trying to beat somebody.

194. Alcohol and the muscles.—Men use alcohol to make themselves strong. It dulls their weak feelings, and then they think themselves strong. They are really weaker. The alcohol hinders digestion and keeps food from the cells. Then the fires in the body burn low, and there is little strength.

Alcohol sometimes causes muscle cells to change to fat. This weakens the muscles.

Men sometimes have to do hard work in cold countries; and at other times they must make long marches across hot deserts. Neither the Eskimos in the cold north, nor the Arabs in the hot desert, use strong drink. Alcohol does not help a man in either place. It really weakens the body. The government used to give out liquor to its soldiers; but soldiers can do more work and have better health without liquor and it is no longer given out.

A few years ago men were ashamed to refuse to drink. Even when a new church building was raised, rum was bought by the church and given to the workmen. Farmers used to give their men a jug of rum when they went to work. Farm hands would not work without it.

Now all this has changed. Men do not want drinkers to work for them. A railroad company will discharge a man at once if he is known to drink at all. A man can now refuse to drink anywhere and men will not think any less of him. 195. Tobacco poisons the muscle cells and makes them weak. At first it makes boys too sick to move. It always poisons the cells even if they do not feel sick.

196. A long life.—A man's body is built to last eighty years, but only a few live so long. If you are careful in your eating and drinking, if you breathe pure air, and if you use your muscles, your body will be healthy and will last the eighty years and more. All through your life you will be strong and able to do good work.

WHAT WE HAVE LEARNED