202 PRINCIPLES OF ANIMAL NUTRITION. 
the organism economizes in its demands for proteids elsewhere than 
in the muscles. The further interesting observation was made that 
with continuous work the proteid metabolism, which at first showed 
an increase, diminished again and even reached its original value. 
With a ration containing but little protein and much non-nitrogenous 
material, a small increase of the proteid metabolism was observed 
as the result of work. The preliminary account of the experi- 
ments affords no adequate data for computing the sufficiency of 
the total food. 
Krummacher,* in his second investigation, made three separate 
experiments. In the first of these the total food was estimated to 
be approximately sufficient for maintenance (38 Cals. per kilogram), 
while in the other two it was much in excess of this. The following 
table shows the total amount of food per kilogram, expressed as 
Calories of metabolizable energy,t the amount of work performed, 
and the percentage increase of the proteid metabolism: 
Energy of Food. Increase 
Work of Proteid 
Measured, | Metabolem, 
Total. Per Kg. Bm. Per Cent. 
Cals. Weight. Cals. 
Experiment I............ 2459 38 153,070 21 
me 1d reer ae 5034 64 324,540 22 
Tilse one eras 5701 72 401,965 7 
The work done consisted in turning an ergostat. It has been 
shown by subsequent investigators that not over 30 per cent. of 
the energy of the body material metabolized in the performance of 
work in this way can be recovered in the work actually done. 
Assuming this high figure, and further that Krummacher’s esti- 
mate of the maintenance requirements is accurate, it appears that 
the food in these experiments was insufficient to supply the energy 
required for the amount of work actually done. 
It was observed, as in other experiments of this nature, that the 
increased excretion of nitrogen continued for a day or two after the 
cessation of the work. Only in the first experiment, however, was 
even the total proteid metabolism during the periods of work, to- 
gether with the excess above the rest value observed on succeeding 
* Zeit. f. Biol., 33, 108. t See Chapter X, 
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