Fig. 4 —General plan of the organs of the body.
The muscle is fastened to the bones which support the body and give it stiffness. The muscle by pulling on the bones helps the body to do all kinds of work. The muscles and bones cannot work day after day without being fed. For this reason a food tube leads from the mouth down into the trunk to prepare milk, meat, bread, or other food, for the use of the body.
Feeding the Body.—The mouth receives the food and chews it so that it may be easily swallowed. It then goes into a sac called the stomach. Here the hard parts are broken up into tiny bits and float about in a watery fluid. This goes out of the stomach into a long crooked tube, the intestine. Here the particles are made still finer, and the whole mass is then ready to be carried to every part of the muscles, bones, and brain to build up what is being worn out in work and play.
Carrying Food through the Body.—In all parts of the body are little branching tubes. These unite into larger tubes leading to the heart. Through these tubes flows blood. Hundreds of tiny tubes in the walls of the intestine drink in the watery food, and it flows with the blood to the heart. The heart then pushes this blood with its food out through another set of tubes which divide into fine branches as they lead to every part of the body ([Fig. 5]).
Getting rid of Ashes and Worn-out Parts.—The body works like a machine. Food is used somewhat as a locomotive uses coal to give it power to work. Some ashes are left from the used food, and other waste matter is formed by the dead and worn-out parts of the body. This waste is gathered up by the richly branching blood tubes and carried to the lungs. Here some of it passes out at every breath. Part of the waste goes out through the skin with the sweat and part passes out through the kidneys. In this way the dead matter is kept from collecting in the body and clogging its parts.
How the Parts of the Body are made to work Together.—The mass of red flesh covering the bones is made up of many pieces called muscles. Whenever we catch a ball or run or even speak, more than a dozen muscles must be made to act together just in the right way. When food goes into the stomach, something must tell the juice to flow out of the walls to act on the food. The boss or manager of all the work carried on by the thousands of parts of the body is known as the brain and spinal cord with their tiny threads, the nerves, spreading everywhere through bones and muscles. The brain and spinal cord give the orders and the nerves carry them ([Fig. 5]).
The Servants of the Body.—The parts of the body are much like the servants in a large house or the clerks in a store. One servant or clerk does one kind of work while another does something entirely different. Each portion of the body does a different kind of work. Each one of these parts doing a particular work is called an organ. The stomach is an organ to prepare food and the heart is an organ for sending the blood through the body.
