This can be done by means of a wide rubber strap, one end of which is fastened to the frame of the door near the hinge, and the other end to the door, out near its edge. When we push open the door, the rubber strap is stretched; but as soon as we have passed through, the strap tightens, draws the door back, and shuts it. If you stretch out your right arm, and clasp the upper part tightly with your left hand, then work the elbow joint strongly back and forth, you can feel something under your hand draw up, and then lengthen out again, each time you bend the joint. What you feel, is a muscle (mŭs´sl), and it works your joints very much as the rubber strap works the hinge of the door. One end of the muscle is fastened to the bone just below the elbow joint; and the other end, higher up above the joint. When it tightens, or contracts, as we say, it bends the joint. When the arm is straightened, the muscle returns to its first shape. There is another muscle on the outside of the arm which stretches when this one shortens, and so helps the working of the joint. Every joint has two or more muscles of its own to work it. Think how many there must be in our fingers! If we should undertake to count all the muscles that move our whole bodies, it would need more counting than some of you could do. TENDONS. You can see muscles on the dinner table; for they are only lean meat. [Illustration: _Tendons of the hand._] They are fastened to the bones by strong cords, called tendons (tĕn´dŏnz). These tendons can be seen in the leg of a chicken or turkey. They sometimes hold the meat so firmly that it is hard for you to get it off. When you next try to pick a "drum-stick," remember that you are eating the strong muscles by which the chicken or turkey moved his legs as he walked about the yard. The parts that have the most work to do, need the strongest muscles. Did you ever see the swallows flying about the eaves of a barn? Do they have very stout legs? No! They have very small legs and feet, because they do not need to walk. They need to fly. The muscles that move the wings are fastened to the breast. These breast muscles of the swallow must be large and strong. EXERCISE OF THE MUSCLES. People who work hard with any part of the body make the muscles of that part very strong. The blacksmith has big, strong muscles in his arms because he uses them so much. You are using your muscles every day, and this helps them to grow. Once I saw a little girl who had been very sick. She had to lie in bed for many weeks. Before her sickness she had plenty of stout muscles in her arms and legs and was running about the house from morning till night, carrying her big doll in her arms. After her sickness, she could hardly walk ten steps, and would rather sit and look at her playthings than try to lift them. She had to make new muscles as fast as possible. Running, coasting, games of ball, and all brisk play and work, help to make strong muscles.