The fat contains the largest amount of carbon.
The brain, the nerves, and the bones contain the largest proportion of phosphorus compounds.
Yet, while the brain contains phosphorus, and the tissues nitrogen, the brain cannot be built up by eating elementary phosphorus, nor the muscles by pure nitrogen, but compounds rich in phosphorus or nitrogen may be utilized.
Plants use the simple compounds of the earth, air, and soil, and, within their own cells, build them up into such complex substances as starch, sugar, protein, fat, and salts, putting them in condition for man and other animals to appropriate to their use.
All plant life is compounded from the elements in the soil, air, and water, by the action of the sun’s rays. The rays of heat and light store something of their power in latent heat and energy in these plant compounds.
The end of plant life is the completion of its compounds—when it has matured them, the plant dies.
All organic matter is thus formed by the action of the sun’s rays on inorganic matter.
The gluten of wheat is formed from the chemical union of nitrogen in the air and nitrogen in the soil with other substances.
The starch of wheat and other grains is from carbon which the plant has taken from the soil and combined with other substances.
All meats are largely derived from plants which have appropriated the elements from the soil, water, and air. The chemical processes of the animal convert the energy latent in the plant foods into the more concentrated form of meat. The animal thus performs a part of the chemical work for man—the digestive organs of one animal convert the food contained in certain plants, into a substance more easily assimilated by another animal.