_Milk sugar_ needs less chemical change than other sugars and is taken almost at once into the circulation. It is contained in the natural food for the infant. The digested sugar (grape sugar) is further changed in the body into glycogen. When an excess of sugar or starch is consumed, it is stored within the body as glycogen, until required. Sugar is perhaps a better food than starch, because less force is required for its digestion and it is easily assimilated, being more readily converted into dextrose than are starches.[3] Moreover it furnishes the heat and energy needed by those having small power to digest starch. Sugar is soon oxidized, and, for this reason may be eaten by those who need to use an extra amount of muscular strength, or to get strength quickly. It yields heat and energy within thirty minutes after eating, and in times of great exertion or exhausting labor, the rapidity with which it is assimilated gives it advantage over starch. Because it is so quickly converted into energy it is valuable for children at active play. Experiments with soldiers on forced marches, and in Arctic explorations, have shown the value of sugar as a food, in enabling the men to withstand hunger, thirst, and fatigue. Taken in excess, however, particularly by those of sedentary habits, it clogs the system as does any other excess of material, creating difficulties for the liver and kidneys. During muscular activity, four times as much sugar is consumed in the body as is ordinarily used in the body processes. Used in limited quantities, therefore, according to the muscular or brain power exercised, sugar is one of the best foods for the production of energy. When much sugar is eaten the starches and fats in the food should be lessened to avoid overloading the system. When eaten in excess, sugar may temporarily appear in the urine unaltered. It might be inferred that, as all starch must be converted to sugar before it can be used by the body, starches might be discarded and replaced by sugars. A small quantity of sugar, however, soon surfeits the appetite, and if the foods were confined to those having a surplus of sugars, sufficient food would not be eaten to supply other needs of the body. This lack of appetite occasioned by an excess of sugar is due, partly, to the fact that the gastric juice is not secreted so freely when there is much sugar in the stomach. Because of the slower secretion of gastric juice and the surfeit of the appetite occasioned by them, sweetened foods should not be used at the beginning of a meal, and, while a moderate amount of sugar is desirable, a surfeit will cause indigestion. This is particularly liable when one eats sufficient starch and sugar at a meal and then eats candy between meals.