It must be said, in justice, however, that housewives are responsible for many of these productions. Dealers who would be glad to sell only pure articles say that “the trade won’t have them.” Many insist on a highly colored cheese, thinking that the color denotes greater richness, whereas a little reasoning would show them that the richest old cheeses are pale in color, the deeper color of the cheese being due to the addition of coloring matter to the curd. While the coloring matter is not deleterious, the color is no evidence of richness. Highly colored green pickles, beans, and peas, should not be used. Pickles which are hard and crisp are usually made so by alum. Brilliant red catsup is in demand, though the pure variety is known by its darker and not so attractive hue. High coloring in any canned fruit or vegetable is usually an indication that dye stuffs have been used to produce it. Fruit jams which are of nondescript color or pale when pure are colored artificially because the ordinary purchaser demands a pretty product. Through the vigilance of the food inspectors of the boards of health, and because of some vigorous prosecutions, the adulteration of the people’s food is, however, not so easy and profitable an occupation as formerly. The Bulletins of the Department of Agriculture furnish a mine of wealth in the gaining of knowledge of various foods and their preparation, and may be had free on application to this Department at Washington. _HEAT AND ENERGY_ The second use of foods, as mentioned before, is to furnish heat and energy for the work of the body. Heat and energy are produced _automatically_ by the action of the heart, the movement of the lungs in breathing, and by muscular activity through the digestion, absorption, and assimilation of food elements, and through the activity in tearing down and eliminating waste. They are produced _consciously_ by muscular activity in exercise. Just as any engine requires fuel, water, and air to create the force necessary to run the machinery, so does the human engine require fuel, air, and water. The fuel for an engine consists of coal, wood, or oil. As these are brought in combination with oxygen, combustion or oxidation takes place, liberating heat and setting the engine in motion. The amount of energy or force given off by an engine should exactly equal the amount of latent energy provided in the fuel. Much of this energy is commercially lost, since much of the latent force in fuel is not fully liberated, some passing off in the smoke, while some may remain in the cinders. The amount of heat and energy generated by the body equals the amount of latent energy released by the burning of food material during oxidation. The carbohydrates and fats constitute the most of the fuel. The body cells are constantly surrounded by the lymph which contains the food material—the protein, the carbohydrate, and the fat.