In this balance period of six days the average daily intake of nitrogen was 7.83 grams, coupled with an average fuel value of the food per day of 1975 calories. This latter value was obviously too small for a man of Dr. Mendel’s body-weight, and doing the amount of physical work he was called upon to perform. Being on one’s feet in a laboratory six to eight hours a day, in addition to the ordinary activity of a vigorous man leading a strenuous life, necessitates the utilization and oxidation of considerable food material. The average daily output of nitrogen through the urine amounted to 7.50 grams, considerably above the average daily excretion for the seven months’ period. Still, under these conditions there was a minus balance of 7.13 grams of nitrogen for the six days’ period, indicating that the body was drawing upon its stock of proteid material to the extent of 1.19 grams of nitrogen per day. This does not necessarily mean that the body had need of that additional amount of proteid matter each day, but rather that the amount of total energy required was beyond the potential energy supplied by the food. There not being sufficient non-nitrogenous food at hand, the body was compelled to draw upon its own resources, and in so doing utilized some of its tissue proteid. This is made quite clear by the results of the second balance period shortly to be described. It is evident, however, that while the body was not in nitrogen equilibrium for this particular period of six days, there must have been a general condition of both body and nitrogen equilibrium, otherwise the body-weight would not have remained practically stationary for so long a period as from February 7 to June 20. Commencing May 18, a second nitrogen balance was attempted, in which, as in the preceding case, there was a careful comparison of income and output for seven days. There was as before a free choice of food, but it was essentially vegetable in character. A greater variety of foods was taken, however, and an effort was made to have the non-nitrogenous food somewhat more liberal in amount, though in as close harmony as possible with the desires of the appetite. _Wednesday, May 18, 1904._ Breakfast.—Banana 92 grams, bread rolls 28 grams, cream 50 grams, coffee 150 grams, sugar 21 grams. Lunch.—Bread 66 grams, soup 150 grams, farina 154 grams, sweet potato 123 grams, beans 70 grams, syrup 50 grams, coffee 150 grams, cream 50 grams, sugar 14 grams. Dinner.—Bread 42 grams, consommé 100 grams, spinach 100 grams, mashed potato 250 grams, apple pie 97 grams, coffee 150 grams, cream 50 grams, sugar 21 grams. Food. Grams. Per cent Nitrogen. Total Nitrogen.