In several parts of the world restricted diets of a monotonous character have for centuries produced diseases in man. The only one of these which was at all common in the Western hemisphere was, scurvy. This disease caused much suffering among sailors in the days of the long voyages before the advent of steam navigation. It was well understood from the early part of the eighteenth century that scurvy was the result of the consumption of a faulty diet composed usually of biscuits and salt meats. It was also known that prompt recovery resulted from the consumption of liberal amounts of fresh fruits and vegetables. Decades passed without any systematic attempt being made to determine the cause of the peculiar value of this class of foods.

Pellagra has been a scourge among the poorest peasants in some parts of Italy and France for centuries, and its etiology has been referred by many to the poor quality of the simple and monotonous diet. This disease was not observed in America until after 1900. After that time it increased rapidly up to 1917, especially in the Southern States.

Bcri-beri is a disease common among the poorest classes of the Orient, who limit their food supply principally to polished rice and fish. It is remarkable that not until the year 1897 was the first fertile suggestion made as to the nature of the dietary fault which was responsible for the development of this disease. This observation was made by the Dutch physician, Eijkman.

Man has been sufficiently industrious in most parts of the world to secure for himself a varied diet, which he derives from the cereal grains and legumes, fruits, roots, tubers, meats and certain edible leaves. Beginning with the dawn of the era of his most rapid advance toward achievement, he has in many parts of the world been the possessor and protector of flocks and herds, which provided him with clothing and a constant supply of meat and milk. The importance of this last item in his food supply we have but recently come to appreciate. The famous chemist, Van Helmont, called milk "brute's food," and thought it advisable to substitute for it bread boiled in beer and honey. Baron Liebig likewise thought of preparing a substitute for milk in his "Food for Infants." In later chapters of this book it will be made clear how tragic it is for the health of an infant to attempt to replace the most important single human food by some mixture made up on the basis of chemical composition in imitation of human milk. It is with a view to establishing an appreciation of the great differences in the nutritive value of foods the composition of which is such as to make them appear alike from the results of chemical analysis, that the present account of the progress attained by the investigations of recent years was prepared.