ANIMAL HEAT
The source of heat in the animal body was the subject of much superstitious speculation on the part of ancient scientists. It is now known that animal heat is derived from the food we eat by means of a peculiar process of vital oxidation—effected in the presence of oxygen—by the action of water and enzymes upon the food elements absorbed by the living cell. This process of oxidation liberates the heat and energy stored by the sun in the food, and thus the body is kept warm by this constant combustion of the digested foodstuffs. The starches and sugars, together with the fats, represent food elements which serve as the body's fuel. By this means we are able to maintain a constant body temperature of almost one hundred degrees.
The average human body produces enough heat every hour to raise two and one-half pounds of water from the freezing point to the boiling point. This is equivalent to boiling about seven gallons of ice-water every twenty-four hours. Differently expressed, the body gives off each hour the same amount of heat as a foot and a half of two-inch steam coil. This is the same amount of heat which would be produced by burning about two-thirds of a pound of coal.
FUEL VALUE OF FOODS
Expressed in terms of English weight, the fuel value of the three different food elements would be:
| 1 ounce of carbohydrates | 127.5 calories |
| 1 ounce of proteins | 127.5 " |
| 1 ounce of fat | 289.2 " |
It will be observed that fat contains more than twice as much heat as the carbohydrates. This is due to the fact that fat contains more carbon than either starch or sugar. Next to fats, starches and sugars are the most important fuel elements. Protein is a very extravagant form of food for fuel purposes. Proteins are the most expensive elements of human food; they are incompletely burned in the body, and inasmuch as they leave behind distressing and disease-producing ashes, it is clearly evident that only sufficient amount of proteins should be eaten each day to supply the demand of the body for repairs. We should depend more largely upon the carbohydrates and fats for heat and energy.
A large part of our food is required to furnish heat to take the place of that lost by radiation from the skin, and this is why children require more food than adults—they have a larger skin surface in proportion to their weight, and therefore lose more heat by radiation, and it is for this reason that the food for the growing child must be wisely and carefully selected.
DIET FOR CHILD TWO TO THREE YEARS OLD
Breakfast, 7-8 a. m.: Fruit; cooked or toasted cereal served with thin cream; a soft boiled or coddled egg; bread (two or more days old) and butter; plenty of milk.