Only within a few years have scientists awakened to the importance of the nitrogen part of our food, consequently the subject of nitrogen starvation is so new that it is popularly unknown. As it is the particular form of modern underfeeding, its discussion is of more than ordinary importance. Not only does it prove that there is overpopulation in every part of the world at the present moment, but the facts elicited are of enormous hygienic importance in that they show very clearly the dreadful results of improper feeding, rather than lack of all food.
The chemists of the last generation inflicted almost irreparable damage on the science of dietetics, from which it is just recovering. The first organic substances investigated were the starches, sugars, alcohols and similar carbon compounds excreted by living cells - just as honey is excreted by the bee. Hence, the idea grew up that the basis of living tissues or the center around which all organic compounds are built, is an atom of carbon, and it is still taught here and there. The real truth has not yet been fully grasped - every living substance is a nitrogen compound. All the other included substances like sulphur, phosphorus, carbon, hydrogen, oxygen and iron are built around the nitrogen atom.
The food of both plants and animals is composed essentially of nitrogen and oxygen. Carbon is essentially a fuel, and its compounds are burned up to produce heat and energy, though of course, nitrogen compounds (proteids) can also burn up to furnish heat and energy. Indeed, one scientist* actually asserted that the nitrogen compounds are the only source of muscular strength. The law applies to man as well as bacteria, for neither can grow or flourish without nitrogen. The young ovum of man feeds upon proteid exclusively for awhile, but as it grows larger and larger it needs carbon and other things in fats, starches and sugars. Consequently, the proportionate amount of animal food, or rather nitrogen, is greatest in infancy, and progressively diminishes until growth is finished, when only sufficient is needed to keep up repairs. As age progresses, less nitrogen is needed for repairs, so that we find the diminution of proteid food continues until it is reduced to a very small amount in old age. Carbon compounds, fats, sugars, etc., are like the fuel of a locomotive, and are needed in amounts proportionate to the heat or work expended. Men in cold countries must eat more of them than in hot, and muscle workers need more than the sedentary. A small slow ship burns less than a big fast one, and each needs more in winter than in summer. The number of men who can live in a place is, then, essentially dependent upon the amount of nitrogen available. Consequently the whole problem of the future centers around the nitrogen question. If the nitrogen gives out, the people disappear, and if it is abundant, dense populations are possible.
Nitrogen salts are first taken from the soil in solution by the rootlets of plants and stored up for animals. Man sometimes gets his nitrogen from the grains, fruits, nuts, peas and beans, and sometimes he takes it in milk, eggs and flesh of animals, who in their turn have received it from plants. We often exhaust a thin soil of its nitrogen by a few crops and the farms become worthless unless the nitrogen is put back. Von Liebig asserted that the real reason for the decline of ancient civilizations, particularly Rome, was the rapid exhaustion of nitrogen from the soil. In Egypt, the annual floods renew the supply in the mud deposited. Of course, there are other ways of exhausting a soil, for plants need other things from the earth, but we are here dealing with the nitrogen solely. We find, then, that if a farm is to continue to produce food, nitrogen must be constantly supplied to it by manures or guano or one of the other numerous kinds of nitrogenous fertilizers. The nitrogen compounds are broken up by the soil bacteria into soluble compounds and absorbed by the rootlets in the water they take up. The whole question of food resolves itself into a matter of obtaining nitrogen to put into wheat and corn and hay. We need not discuss the production of artificial foods because they all come from the soil eventually. We are limited to the amount of vegetation we can produce, i.e., our nitrogen and the amount of the sun's energy we can capture in this way, for we are rooted to the soil.