No one will be likely to dispute the statement that most people are unwell, and that their failures, indiscretions, fits of temper, tendency to complain, tendency to give themselves up to reflecting on the possibilities for everything going wrong, their lack of enthusiasm and other qualities which contribute to making them unhappy and inefficient creatures, are in great measure the result of ill health. We must grant that hereditary mental defects are widespread and are inherited as are other mental tendencies, but who can say how frequently the confirmed grouch is not what he is because of disturbances in his metabolic processes. The peevishness and unreasonableness of persons convalescing from serious diseases is a matter of common knowledge. Intolerance tends to develop in those who are continually in low spirits, and there can be no reasonable doubt that the diet may deviate from the optimal even in the United States, to a degree which can easily cause the results we see. It has produced comparable effects in our rat colony, when the choice of food was entirely comparable to human experience here.

Under faulty nutrition the machinery of the body tends to break down in places and with frequency. The exact nature of the defects which develop cannot in general be traced to their ultimate causes. Chemistry and histology have now made it clear that the functions of living matter depend solely upon the chemical complexes contained therein, and especially on the structure or organization, of its components. Its peculiar properties depend upon its structure. This is not homogeneous, but affords a wide variety of types which are revealed by histological methods. It is the minute structure of the protoplasm which suffers change when the nutritive conditions deviate from the optimal, and the result is faulty operation and an abnormal human being or animal. We have become well aware how very slight changes in the chemical or physical conditions may make pronounced differences in the properties of emulsions or of colloidal solutions. It has been demonstrated in our study of the effects of varying the ratios between calcium and phosphate in the diet on the histological picture of the bones, that equally small deviations from the optimal composition of the food may in certain cases, produce profound changes in the manner of organization of the finer structures of the living tissues. Function, too, has been shown to deviate to a degree comparable with the histological changes.