Under normal conditions the temperature of the body may be thoroughly controlled by feeding. The principal process of metabolism is that of making heat out of the fuel given to the "human boiler." The amount of heat, therefore, that a given quantity of food will produce is determined very largely by the amount of resistance that is met from natural environment. [Sidenote: Amount of fat required in different temperatures] The human body, under ordinary conditions, in a temperature of 60° Fahrenheit, will use about two ounces of pure fat every twenty-four hours. If the temperature should drop to 30° Fahrenheit, it would require about three ounces of fat every twenty-four hours to keep the temperature of the body at normal. Under certain conditions of exposure it might require as much as five and even six ounces of pure fat to maintain normal temperature of the body, and in the extreme north, where the temperature ranges in winter from 25° to 30° below zero, the natives often take as much as sixteen ounces of fat during the day. Fat being the principal heat-producing element, it is, therefore, the most necessary thing to consider in a temperature of extreme cold. The student will readily understand that, in order to maintain a normal standard of vitality and endurance, the selection of foods must be made according to age, activity, and temperature. For a person undergoing a reasonable amount of exposure, and working in a climate where the temperature is ranging between 20° and 30° Fahrenheit, the following menus, covering one day, may be suggested: Immediately on rising, drink a cup of hot water, then take vigorous deep breathing exercises, followed by a cool sponge bath and rub down. BREAKFAST (An hour later) Add half an ounce of sugar to two or three eggs, and whip five minutes; add a tablespoonful of lemon juice while whipping; mix with this two glasses of rich milk A tablespoonful of nuts One very ripe banana, with cream LUNCHEON One fresh vegetable Lima or navy beans A salad, with either olive-oil or nuts A baked potato or boiled wheat (A liberal supply of butter or cream) DINNER A baked sweet potato One or two vegetables Eggs, or buttermilk, unskimmed A baked white potato, with either olive-oil or butter Dates, with cream cheese, or gelatin, with cream As the temperature becomes lower, the amount of fats and proteids should be increased according to exposure and activity. The student should bear in mind that carbohydrates, proteids, and fats are the most important factors in the winter dietary. Other articles can be held level over a wide range of temperature, provided these three staple nutrients are taken in the requisite proportions. [Sidenote: Summer diet requires scientific consideration]