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Being HerePage Oh Two Four |
Being HereIntro One Intro Two Intro Three Intro Four Sitemap |
Page Oh Two FourThen, too, there are more uses for food than the production of heat. Teeth and bones and nails need a constant supply of mineral matter, and mineral matter is frequently found in greatest abundance in foods of low fuel value, such as lettuce, watercress, etc., though practically all foods yield at least a small mineral constituent. When fuel values alone are considered, fruits have a low value, but because of the flavor they impart to other foods, and because of the healthful influence they exercise in digestion, they cannot be excluded from the diet. Somewhat as a house is composed of a group of bricks, or a sand heap of grains of sand, the human body is composed of small divisions called cells. Ordinarily we cannot see these cells because of their minuteness, but if we examine a piece of skin, or a hair of the head, or a tiny sliver of bone under the microscope, we see that each of these is composed of a group of different cells. A merchant, watchful about the fineness of the wool which he is purchasing, counts with his lens the number of threads to the inch; a physician, when he wishes, can, with the aid of the microscope, examine the cells in a muscle, or in a piece of fat, or in a nerve fiber. Not only is the human body composed of cells, but so also are the bodies of all animals from the tiny gnat which annoys us, and the fly which buzzes around us, to the mammoth creatures of the tropics. These cells do the work of the body, the bone cells build up the skeleton, the nail cells form the finger and toe nails, the lung cells take care of breathing, the muscle cells control motion, and the brain cells are responsible for thought. |
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