The sugars are also widely distributed substances, and include the cane, grape, malt, maple, and milk sugars. Here also belong the gums and cellulose found in fruit, cereals, and all vegetables which form the basis of the plant cells and fibers. Honey, molasses, and manna are included in this class. The physiological value of the starches and sugars lies in the fact that they are oxidized in the body, and a certain amount of energy is thereby liberated. The energy of muscular work and of the heat of the body comes largely from the oxidation, or destruction, of this class of foods. Now, inasmuch as we are continually giving off energy from the body, chiefly in the form of muscular work and heat, it is evident that material for the production of this energy must be taken in the food. The carbohydrates constitute the bulk of our ordinary food. 104. Fats and Oils. These include not only the ordinary fats of meat, but many animal and vegetable oils. They are alike in chemical composition, consisting of carbon and hydrogen, with a little oxygen and no nitrogen. The principal kinds of fat used as food are the fat of meat, butter, suet, and lard; but in many parts of the world various vegetable oils are largely used, as the olive, palm, cotton seed, cocoanut, and almond. The use of the fats in the body is essentially the same as that of the starches and sugars. Weight for weight they are more valuable than the carbohydrates as sources of energy, but the latter are more easily digested, and more easily oxidized in the body. An important use of fatty foods is for the maintenance of the bodily heat. The inhabitants of Arctic regions are thus enabled, by large use of the fat and oil from the animals they devour, to endure safely the severe cold. Then there is reason to believe that fat helps the digestion of other foods, for it is found that the body is better nourished when the fats are used as food. When more fat is consumed than is required to keep up the bodily heat and to yield working power, the excess is stored up in various parts of the body, making a sort of reserve fuel, which may be drawn upon at any future time. 105. Saline or Mineral Foods. All food contains, besides the substances having potential energy, as described, certain saline matters. Water and salts are not usually considered foods, but the results of scientific research, as well as the experience of life, show that these substances are absolutely necessary to the body. The principal mineral foods are salt, lime, iron, magnesia, phosphorus, potash, and water. Except common salt and water, these substances are usually taken only in combination with other foods. These saline matters are essential to health, and when not present in due proportion nutrition is disturbed. If a dog be fed on food freed from all salines, but otherwise containing proper nutrients, he soon suffers from weakness, after a time amounting to paralysis, and often dies in convulsions.