With maintenance of body-weight, together with nitrogen equilibrium through all these months; and with health, strength, and mental and physical vigor unimpaired, there is certainly ground for the belief that the real needs of the body were as fully met by the lowered consumption of proteid food as by the quantities called for by the customary standards. Finally, it should be noted that this particular subject was small in weight, and hence did not need so much proteid as a man of heavier body-weight would require. In recognizing this principle, we may for future comparison calculate the nitrogen requirement of the body, on the basis of the present results, per kilo of body-weight. With the weight of the subject placed at 57 kilos, and with an average daily excretion of nitrogen amounting to practically 5.7 grams, it is plain that this individual was quite able to maintain a condition of equilibrium with a metabolism of 0.1 gram of nitrogen per kilo of body-weight. Translated into terms of proteid matter, this would mean a utilization by the body of 0.625 gram of proteid daily per kilo of body-weight. Regarding the fuel value of the daily food, we need not be more precise than to emphasize the fact that so far as could be determined, on the basis of chemical composition, the heat value of the food rarely exceeded 1900 calories per day. If we make a liberal allowance, for the sake of precaution, it would seem quite safe to say that this particular individual, under the conditions of life and bodily activity prevailing, did not apparently need of fuel value more than 2000 calories per day, which would correspond to 35 calories per kilo of body-weight. Let us turn now to the second subject in this group, a man of 76 kilos body-weight, 32 years of age, and of strong physique. His active life in the laboratory called for greater physical exertion than the former subject, and consequently there was need for greater consumption of non-nitrogenous food, with the accompanying increase in fuel value of the day’s ration. As in the preceding case, there was no prescribing of food, but a gradual and voluntary diminution of proteid material. During the last seven months and a half of the experiment, the average daily excretion of nitrogen through the kidneys amounted to 6.53 grams, equivalent to a metabolism of 40.8 grams of proteid matter daily; a little more than one-third the minimal quantity called for by common usage. At first, the body-weight of the subject gradually fell until it reached 70 kilos, at which point it remained fairly constant during the last five months. That the quantity of food taken was quite sufficient to maintain the body in a condition of nitrogen equilibrium is apparent from the results of a comparison of income and outgo of nitrogen, as shown in the following table: