THE RELATIONS OF METABOLISM TO FOOD-SUPPLY. 1 35 
animal. The results obtained by E. Voit & Korkunoff * regard- 
ing the minimum requirement upon an exclusive proteid diet have 
already been stated in the first section of this chapter (p. 95). The 
same investigators have also studied the more interesting question 
of how far the necessary proteid supply can be reduced in the 
presence of non-nitrogenous nutrients. 
PRoTEIDS AND Fat.—The experiments were upon the same 
general plan as those just referred to on proteids alone. Beginning 
with an insufficient quantity of proteids, the amount was gradually 
increased, that of the fat remaining constant, until nitrogen equi- 
librium was reached. As in those experiments, too, the nitrogen 
of the food was practically all in the proteid form, and its amount 
is compared with the proteid nitrogen excreted, it being assumed 
that 18.45 per cent. of the urinary nitrogen was derived from the 
extractives of the flesh metabolized in the body. To the writer it 
would seem that a more suitable unit would be the total excretory 
nitrogen, since the proteids of the food had to make good the loss 
of extractives as well as of true proteids from the body, and the 
former loss is as unavoidable as the latter. Accordingly, the results 
have been stated in the table below in both ways. 
Two series of experiments were made: one in which the total 
food-supply was less than was required to supply the estimated 
demands of the body for energy, and one in which it considerably 
exceeded that demand, with the following results: 
Per Cent. of Energy | Mivimum of Food Nitrogen, 
Total Demand Supplied by 
: Per Cent of Fasting 
E: tion, ; 
Fasting, Total Amount, Metabolism, 
oe Per Gent. Food, Grms. Total, | Proteid, 
Per Cent. Per Cent./Per Cent 
Series I: i 
Experiment 1 ....) 4.85 72 90 7.63 157 193 
ee 2 cee} 4.22 73 86 |>5.61 |>1383 |>163 
Series II: 
Experiment 3 ....| 4.98 116 128 |>6.61 |[>1383. |>162 
a 4....| 4.01 127 140 §.12 128 157 
ee 5 ....| 3.86 137 150 5.07 131 161 
The authors also compute from experiments by C. Voit and by 
Rubner percentages lying between 162 and 207, and state as their 
* Zeit. f. Biol., 32, 58. 
