Читать книгу A Handbook of Health - Woods Hutchinson - Страница 16

Food is Fuel. Now what is the chief quality which makes one kind of food preferable to another? As our body machine runs entirely upon the energy or "strength" which it gets out of its food, a good food must have plenty of fuel value; that is to say, it must be capable of burning and giving off heat and steaming-power. Other things being equal, the more it has of this fuel value, the more desirable and valuable it will be as a food.

From this point of view, foods may be roughly classified, after the fashion of the materials needed to build a fire in a grate or stove, as Coal foods, Kindling foods, and Paper foods. Although coal, kindling, and paper are of very different fuel values, they are all necessary to start the fire in the grate and to keep it burning properly. Moreover, any one of them would keep a fire going alone, after a fashion, provided that you had a grate or furnace large enough to burn it in, and could shovel it in fast enough; and the same is true, to a certain degree, of the foods in the body.

How to Judge the Fuel Value of Foods. One of the best ways of roughly determining whether a given food belongs in the Coal, the Kindling, or the Paper class, is to take a handful or spoonful of it, dry it thoroughly by some means—evaporating, or driving off the water—and then throw what is left into a fire and see how it will burn. A piece of beef, for instance, would shrink a good deal in drying; but about one-third of it would be left, and this dried beef would burn quite briskly and would last for some time in the fire. A piece of bread of the same size would not shrink so much, but would lose about the same proportion of its weight; and it also would burn with a clear, hot flame, though not quite so long as the beef. A piece of fat of the same size would shrink very little in drying and would burn with a bright, hot flame, nearly twice as long as either the beef or the bread. These would all be classed as Coal foods.

Then if we were to dry a slice of apple, it would shrink down into a little leathery shaving; and this, when thrown into the fire, would burn with a smudgy kind of flame, give off very little heat, and soon smoulder away. A piece of raw potato of the same size would shrink even more, but would give a hotter and cleaner flame. A leaf of cabbage, or a piece of beet-root, or four or five large strawberries would shrivel away in the drying almost to nothing and, if thoroughly dried, would disappear in a flash when thrown on the fire. These, then, except the potato, we should regard as Kindling foods.

But it would take a large handful of lettuce leaves, or a big cup of beef-tea, or a good-sized bowl of soup, or a big cucumber, or a gallon of tea or coffee, to leave sufficient solid remains when completely dried, to make more than a flash when thrown into the fire. These, then, are Paper foods, with little fuel value.