“It is often noted that cooked fruits, such as plums, seem much sourer than the raw fruit, and it has been suggested that either the acid was increased or the sugar was decreased by the cooking process. This problem was studied by Sutherst, and, in his opinion, the increased acid flavor is due to the fact that cooked fruit (gooseberries, currants, plums, etc.) usually contains the skin, which is commonly rejected if the fruit is eaten raw. The skin is more acid than the simpler carbohydrates united to form a complex carbohydrate. In some fruits, like the apple, where the jelly-yielding material must be extracted with hot water, the pectin is apparently united with cellulose as a part of the solid pulp. As shown by the investigations of Bigelow and Gore at the Bureau of Chemistry, 40 per cent of the solid material of apple pulp may be thus extracted with hot water, and consists of two carbohydrates, one of which is closely related to gum arabic. That such carbohydrates as these should yield a jelly is not surprising when we remember that they are similar to starch in their chemical nature, and, as every one knows, starch, though insoluble in cold water, yields when cooked with hot water a large proportion of paste, which jellies on cooling. “When fruits are used for making pies, puddings, etc., the nutritive value of the dish is, of course, increased by the addition of flour, sugar, etc., and the dish as a whole may constitute a better balanced food than the fruit alone.”[8] FOOTNOTES: [8] C. F. Langworthy, Ph. D.—In charge of Nutritive Investigations of the United States Experiment Station. DIETS As previously stated, the object of foods is to supply the needs of the body in building new tissue in the growing child; in repairing tissue which the catabolic activity of the body is constantly tearing down and eliminating; and in supplying heat and energy. This heat and energy is not alone for muscular activity in exercise or movement; it must be borne in mind that the body is a busy work-shop, or chemical laboratory, and heat and energy are needed in the constant metabolism of tearing down and rebuilding tissue and in the work of digestion and elimination. In this chapter, a few points given in the preceding pages are repeated for emphasis. The proteins, represented in purest form in lean meat, build tissue and the carbonaceous foods, starches, sugars and fats, supply the heat and energy. An excess of proteins, that is more than is needed for building and repair, is also used for heat and energy; the waste products of the nitrogenous foods are broken down into carbon dioxid, sulphates, phosphates, and other nitrogenous compounds and excreted through the kidneys, skin, and the bile, while the waste product of carbonaceous foods is carbon dioxid alone and is excreted mostly through the lungs.