In the body, combined in various ways, are sixteen chemical elements: Carbon, hydrogen, oxygen, nitrogen, sodium, potassium, magnesium, calcium, phosphorus, iron, sulphur, chlorine, iodine, bromine, flourine and silicon.

For the successful growing of crops there must be present in the soil a definite number of elements in normal amount and combination. Just so for the normal development of human beings, there must be present in the food these sixteen elements in proper amount and proportion.

These are not taken into the body as elements but are built up first into seven elemental food classes. These seven food classes are: carbohydrates, fats, proteins, vitamines, salts, cellulose and water. Any daily food ration not containing these in proper proportion is defective.

Class I

Carbohydrate made up of the chemical elements, carbon, hydrogen and oxygen, includes all starches and sugars and is a fuel food. Its combustion in the body produces heat and energy. The carbohydrates make up a large part of the food value of grains, fruits, and vegetables.

Class II

Fat is another but more concentrated fuel food also containing carbon, hydrogen, and oxygen. This food element we have in butter, oils, fat meats, nuts, egg yolks, olives, in the alligator pear, the soy bean; also to some extent in other legumes, in grains, and in vegetables.

Class III

Protein is the muscle and tissue builder. It contains, in addition to carbon, hydrogen, and oxygen, another very important chemical element called nitrogen, by reason of which it is often spoken of as nitrogenous food. Protein also contains variable amounts of other chemical elements as phosphorus, sulphur, and sometimes iron, but its distinctive element is nitrogen. This food is found in a pure state in egg white, casein of milk, and in lean meat. In a combined form it makes up part of the food value of grains, vegetables, legumes, and nuts.

Class IV

Vitamines, our knowledge of which is still somewhat limited, are doubtless the substances out of which the body makes its internal secretions, digestive enzymes, and the ferments of vegetative life processes. They are found in raw, and in fresh vegetables, in fruit, in raw milk, in the outer covering of grains, and in raw meat.

Class V

Salts, both organic and inorganic, are made up of many different chemical elements and are necessary for blood making and tissue building, for the carrying on of various metabolic and secretory processes, and to maintain the proper alkalinity of all body fluids. They are found principally in fruits, vegetables, grains, and milk, and are located with the vitamines largely under the skin of fruits and vegetables and in or near the outer covering of grain.

Class VI

Cellulose is really a carbohydrate but being practically indigestible, is placed in a class by itself. It makes up the woody framework of fruits and vegetables. Its value is in its bulk which by its presence mechanically stimulates the bowel, thus aiding in normal intestinal peristalsis.

Class VII

Water plays an important part in the many chemical reactions and tissue changes continually going on in the body, it holds the various salts in solution, it makes up the principal part of all body fluids and secretions and, as a circulatory medium, it helps to make it possible for the body to regulate its own temperature.