Arguments predicated on custom, habit, and usage have no physiological basis that appeals strongly to the impartial observer. Man is a creature of habits; he is quick to acquire new ones when his environment affords the opportunity, and he is prone to cling to old ones when they minister to his sense of taste. The argument that because the people of a country, constituting a given class, eat a certain amount of proteid food daily, the quantity so consumed must be an indication of the amount needed to meet the requirements of the body, is as faulty as the argument that because people of a given community are in the habit of consuming a certain amount of wine each day at dinner their bodies must necessarily be in need of the stimulant, and that consequently alcohol is a true physiological requirement. A large proportion of mankind is addicted to the tobacco habit, and to many persons the after-dinner cigar is as essential to comfort as the dinner itself; but would any one think of arguing that tobacco is one of the physiological needs of the body? It is said that dietary studies made all over the civilized world “show that a moderately liberal quantity of protein is demanded by communities occupying leading positions in the world.... It certainly seems more than a remarkable coincidence that peoples varying so widely in regard to nationality, climatic and geographical conditions, and dietetic habits, should show such agreement in respect to consumption of protein and energy.” Again, we hear it said that “whatever may be true of a few individuals, with communities a generally low condition of mental and physical efficiency, thrift, and commercial success, is coincident with a low proportion of protein in the diet.” The writer, however, fails to find evidence in the results afforded by dietary studies that there is any causal relationship between the amount of proteid food consumed and the mental or physical supremacy of the people of a given nation or community. Cause and effect are liable to become reversed in arguments of this kind. It is certainly just as plausible to assume that increase in the consumption of proteid follows in the footsteps of commercial and other forms of prosperity, as to argue that prosperity or mental and physical development are the result of an increased intake of proteid food.