As separate chapters will be devoted to these two classes of substances, little more will be done here than to classify the chief sources of them. The mineral salts enter into the composition of every fluid and structure of the body. Inorganic salts cannot be substituted for them as will be shown in a subsequent chapter. The animal lacks the ability to take the crude elements of the earth and synthesize these into acceptable organic compounds.

Vitamins, of which there are a number, are also produced only by the plant. The animal body is capable of taking certain provitamins and completing their synthesis. But it is not capable of producing vitamins de novo. They serve as enzymes.

Vitamins and organic salts are distributed throughout nature and are present in varying quantities in all food substances. Fruits and fresh vegetables are especially high in them. Fruits and vegetables will be treated in separate chapters. Here we are interested in them, largely as sources of these food substances. Chief among these rich sources of vitamins and salts are:

(1) Succulent (watery, juicy) Vegetables:

Leafy Vegetables--celery, lettuce, kohlrabi, cabbage, spinach, dandelion, endive, turnip tops, mustard, parsley, cauliflower, Brussels sprouts, kale, chard, lotus, cress, field lettuce, romaine, chicory, rhubarb, beet tops, radish tops, etc.

Fruiting Plants--okra (gumbo), cucumbers, squash summer squash, pumpkin, string beans, green peas, corn "in milk" (fresh), etc.

Tubers--Asparagus, beet, carrot, turnip, radish, onion, cone artichoke, rutabaga, garlic, oyster plant (salsify).

(2) Juicy Fruits:

Acid: Orange (sour), lemon, lime, sour apple, grapefruit, pineapple, peach, sour plum, apricot, cranberry, loganberry, pomegranate, strawberry, tomato.

Sub-Acid: Melons--watermelons, musk-melon, cantaloupe, casaba, honey dew, etc.,--sweet grapes, huckleberry, fresh figs, pears, etc.

Many other foods are used, both in America and other parts of the world, but all may be placed in some one or the other of the above classes. Some foods such as nuts, grains and legumes, may be placed in two classes.

The bountiful hand of mother nature has supplied us with an abundant and pleasing variety of foods. This wonderful variety of foods which are designed to please the senses of sight, taste and smell, as well as supply the needs of the body, are all made of but a few simple elements of the soil--"the dust of the earth."

Together with water, oxygen and vitamins, proteins, carbohydrates, fats and minerals form the constituents of the body. These must be taken into the digestive tract and there prepared for the use of the body, before they are allowed to enter the body and before they become part of the body.

The material composing a leaf of lettuce cannot be anything but a leaf of lettuce, until it has died from that state and then, after it has been disintegrated, its elements may be built up into the tissues of man. Digestion is the disintegrating process.

Our present knowledge of the role of digestion in nutrition shows positively that the parental administration of food is without value. The process of digestion disintegrates food into fragments which represent the true nutrients--proteins are reduced to amino acids, carbohydrates to simple sugars, fats to fatty acids and glycerol and it is claimed that ions may be liberated from the organic salts during the process of digestion. These things serve as the structural or metabolic units and nothing else will or can.