Carbon of carbon dioxid taken for food by plants not only purifies the atmosphere but is transformed from carbon that animals and humankind cannot use directly into carbohydrates in the plants which both animals and humankind need and secure in consuming plants. Oils in plants are similarly produced.

Mineral matter plants obtain from the soil through their roots. They associate these in themselves with the other substances of which plants are constituted. It is thus the mineral salts are passed from inorganic (non-living) nature through organic (living) nature in plants to animals and humankind. Such salts are necessary for bone-building, also for such regulation of density of the liquids of the body as will insure their transfusion through body-tissues, which is the need in body-living.

Though many of the salts used by the body can be produced in isolation from plant or other living substance, the body cannot make the same use of them when so made. The mineral salts of fruits are usable by the body and most serviceable to it as they are taken in association with organic matter. It is thus that they exist in vegetables and fruits, in which living plants have grown them into association with the organic substances.

Drugs of the same chemical composition as such salts or any artificial preparations of these are not always so assuredly absorbed. What fruits naturally do when taken into the body to keep it in health cannot be artificially effected. Why this is so is not fully known, but the fact is increasingly recognized and is one cause for increased fruit-consumption.

Protein, the food-constituent that carries nitrogen - an element essential to the life of every living cell - from nature to animals and humankind is built up by plants from compounds plants take from the soil in their living. Leguminous plants do likewise with free nitrogen from the atmosphere.