The most common forms in which protein is used for food are the glutens of the grains, the legumes, nuts, cheese, the white of egg, and lean meat.

STARCHES

The starches are by far the most abundant of all elements in human food. They enter largely into the composition of nearly all plants and seeds. Under the influence of the sunlight, the green-colored plants gather up the CO_{2} of the air and, with the water absorbed from the ground, build up starch. The plant takes all the carbon from which starch is made from the air, but while the atmosphere contains almost eighty per cent of nitrogen, the plant is unable to use it; it must secure its nitrogen from the decaying refuse of the soil. Thus the plant utilizes the waste products found in air and earth in the building of its food substances.

Starch exists in the form of small granules. Since each little starch granule is surrounded by a woody envelope of cellulose, it becomes necessary to cook all starches thoroughly in order to burst this cellulose envelope and thus enable the saliva to begin, and other secretions to continue, the work of digestion.

FRUIT SUGARS

The sugar of fruits represents a form of food requiring practically no digestion; while the sugar found in beets, the cane plant, and the maple tree, must be acted upon by the digestive juices of the intestine before their absorption can take place. During the winter, the maple tree stores its carbohydrates in its roots in the form of starch. With the advent of spring Mother Nature begins the digestion of this starch--actually turns it into sugar--and in the form of the sweet sap it finds its way up into the tree trunk to be deposited in the leaves and bark in the form of cellulose, a process very similar to that performed by digestion in the human body, where starch by digestion is first turned into sugar, and afterwards deposited in another form in the liver and muscles.

Dextrine is a form of sugar resulting from thoroughly cooking or partially digesting starch. There are about twenty-five stages or forms of dextrine between raw starch and digested starch or fruit sugar. Dextrine is found in the brown-colored portions of well-toasted bread.

FATS

Fat is a combination of glycerine and certain fatty acids. As a food, it is derived from both the animal and the vegetable kingdom. Animal fat consists of lard, suet, fat meat, etc., while fat of animal origin is represented by cream, b.u.t.ter, and the yolks of eggs. The vegetable fats are found in nuts, especially the pecan, cocoanut, Brazil, and pine nuts; also in the grains, particularly oats and corn. The peanut also contains a considerable amount of fat. Of the fruits, the banana and strawberry contain a trace of fat, while the olive is the only fruit rich in fat.

As a food, fat is used in three forms. The emulsified form is represented by cream, olive oil, and nuts. When the tiny globules of fat, which are each surrounded by a little film of casein, are crushed--united into a solid ma.s.s--we have a free fat. This form is represented by b.u.t.ter and other animal fats. Another form is fried fat--fat which has been chemically changed by heat with the development of certain irritating acids.

MINERAL SALTS

The mineral elements comprise but a small part of human food as regards weight, but they are extremely important to the health of the child as well as the adult. As found in the food, they are not in the form of mineral salts, like common table salt. The salts of food are living salts, organic or organized salts, such as are found in the growing plant. These salts are of great value to the various fluids of the body, and also as stimulants to nerve action, but more particularly in the work of building up the bones.

Salts are found largely in the cereals. A small amount is also found in vegetables, particularly the potato, as well as in most fruits.

CELLULOSE

Cellulose represents the great bulk of all vegetables and fruits. It is digested by most animals, but in man it is digested only to the extent of about thirty per cent. The presence of a large amount of cellulose in the food enables us often to satisfy the appet.i.te without injury from overeating. It serves to give bulk to the food, and thereby possibly acts as a preventive to constipation.

WATER

Water fills an important place in the nutrition of the body. The food changes in connection with digestion, a.s.similation, and elimination, can take place only in the presence of water. Water const.i.tutes from fifteen to ninety-five per cent of the various foods. The watery juices of vegetables and fruits consist largely of pure, distilled water, in which fruit sugar is dissolved, with added flavoring substances. Water is absolutely essential to the performance of every vital function connected with human metabolism.

ANIMAL HEAT

The source of heat in the animal body was the subject of much superst.i.tious 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 b.u.t.ter; plenty of milk.

_Dinner_, 12-1: Soups; creamed vegetables--tomato, corn, peas, and celery; any two of potatoes--creamed, mashed, or baked--carrots, beets, spinach, peas, cornlet, squash, cauliflower, asparagus tips, string beans; protein dish--the puree of dried beans, peas, or lentils; macaroni or carefully selected meats; dessert--apples, baked or sauce--or other fruits, junket, custard, milk.

_Supper_, 5-6 P. M.: Fruit, bread (bran bread if constipated); milk; porridge, with rich milk or milk toast; sweetened graham crackers.

FOODS ALLOWED CHILDREN OF FOUR YEARS AND OLDER

_Protein Dishes_: Purees of dried peas; lentils; beans; macaroni; eggs--soft boiled, poached, scrambled, or omelette; meats--steak, chops, chicken, turkey, broiled fish.

_Cereals_: All the toasted-flake foods; toasted and not too fresh bread, including both graham and bran; hominy; corn meal; oatmeal; farina; rice; barley; tapioca; sago, etc.

_Soups_: Creamed vegetable soups of all kinds and broths.

_Vegetables_: Potatoes; all the small green vegetables; lettuce; stewed celery; beets; squash; cauliflower, etc.

_Fruits_: All, if stewed or baked. Raw fruits--pears, peaches, ripe apples, berries, oranges, persimmons, grape-pulp without seeds, etc.

_Desserts_: Custard; jellos; junkets; home-made ice cream; sponge cake; baked fruits with whipped cream, etc.

FOODS TO BE AVOIDED BY YOUNG CHILDREN

1. _Doughy breads_, griddle cakes, insides of m.u.f.fins, hot biscuits, etc.

2. _Fried meats_, such as sausage, oysters, pork, ham, veal, salt fish, corned beef, dried beef, etc.

3. _Foods that are hot when they are cold_--such as catsup, horse radish, mustard, highly spiced pickles, sauces, etc.

4. _Rich pastries_, puddings, unripe fruit, salted peanuts, and highly concocted dishes.

5. _Certain salads_, containing coa.r.s.e but easily swallowed foods, with highly seasoned sauces.

6. _Tea, coffee, and all alcoholic beverages._

7. _Soft candies_, chocolate creams, bon-bons, patties, etc.