THE UTILIZATION OF ENERGY. 523 
Diet. Respiratory | Energy, cals. 
Proteids:Onhy ies paisecs acrsrwedes vas Bes yselods 0.78 2.58 
Chiefly faticon cs sus <2 mae auete cs eens moe es Ges 0.74 2.43 
ce ““ (body freed from carbohydrates by 
phloridzin)... 1... cece eects 0.71 2.71 
Much sugar with proteids .................... 0.83 2.58 
« «and little proteids ................ 0.88 2.63 
The differences are quite small, while, as Zuntz points out, if 
2.6 cals. represent the demand for energy per unit of work when 
carbohydrates are the source it should, according to Chauveau’s 
theory, rise to about 3.68 cals. when the energy is derived exclu- 
sively from fat. 
Altogether similar results have been recently reported from 
Zuntz’s laboratory by Heineman,* and by Frentzel & Reach,} in 
experiments on man. 
In Heineman’s experiments the work, which was never exces- 
sive, consisted in turning an ergostat, the respiratory exchange 
being determined by means of the Zuntz apparatus and the total 
urinary nitrogen being also determined. From these data, reckon- 
ing 1 gram of urinary nitrogen equivalent to 6.064 liters of 
oxygen,t the average amount of energy metabolized on the vari- 
ous diets, and the proportion derived respectively from proteids, 
fats, and carbohydrates, is computed. By comparison with rest 
experiments the increments of oxygen and carbon dioxide due to 
the work were determined, and from these the energy consumed 
per kilogram-meter of work was calculated upon three different 
assumptions: first, that the proteid metabolism was not increased 
by the work; second, that it increased proportionally to the oxy- 
gen consumption; third, that as large a proportion of the energy 
for the work was furnished by the proteids as is consistent with 
the observed respiratory exchange. The results are summarized 
in the following table: 
* Arch. ges. Physiol., 88, 441. 
} Ibid., 88, 477. 
¢ Zuntz, Arch. ges. Physiol., 68, 204. 
