METHODS AND APPARATUS 
33 
Using the amount of oxygen absorbed for the combustion in the body of 1 
gram of carbohydrates, fat, or protein, and the well-known heats of combustion 
of these substances, Zuntz has computed that 1 liter of oxygen has a calorific 
value varying from 4.686 to 5.047, according to the character of the material 
burned, the higher values being found for the combustion of carbohydrates 
and the lower for the combustion of fat. Zuntz has also carefully computed 
the changes in value of the calorific equivalent of oxygen, depending upon 
the character of the material burned as indicated by the respiratory quotient. 
Table 4. — Calorific values of 
oxygen. 
Calorific 
Calorific 
Calorific 
Respiratory 
value of 
Respiratory 
value of 
Respiratory 
value of 
quotient. 
1 liter 
quotient. 
1 liter 
quotient. 
1 liter 
oxygen. 
oxygen. 
oxygen. 
Calories. 
Calories. 
Calories. 
0.70 
4.686 
0.80 
4.801 
0.90 
4.924 
.71 
4.690 
.81 
4.813 
.91 
4.936 
.72 
4.702 
.82 
4.825 
.92 
4.948 
.73 
4.714 
.83 
4.838 
.93 
4.960 
.74 
4.727 
.84 
4.850 
.94 
4.973 
.75 
4.739 
.85 
4.863 
.95 
4.985 
.76 
4.752 
.86 
4.875 
.96 
4.997 
.77 
4.764 
.87 
4.S5.7 
.97 
5.010 
.78 
4.776 
.88 
4.900 
.98 
5.022 
.79 
4.789 
.89 
4.912 
.99 
5.034 
.... 
1.00 
5.047 
X 
The Zuntz method of computation assumes that the combustion is 
entirely of fat, or carbohydrate, or a combination of the two, and no recogni- 
tion is made of the fact that a certain amount of protein is also burned. As 
has frequently been pointed out, the amount of protein contributing to the 
energy production seldom exceeds 15 per cent; according to Magnus-Levy,* 
if one considers that 15 per cent of protein is simultaneously burned, the 
calorific value of 1 liter of oxygen would be lowered by 0.031 calorie. Since 
it is incorrect, however, to consider the nitrogen excretion as simultaneous 
with the breaking-down of the protein, Loewy argues that it is much more 
logical in short respiration experiments to use the direct calculations of the 
energy from the values reported by Zuntz and Schumburg. 
Without presuming to pass judgment upon the absolute accuracy b of 
every point in the Zuntz method, and fully recognizing the difficulties inci- 
dental to a comparison of direct and indirect calorimetry in periods of short 
duration, nevertheless we believe that when the metabolism is measured im- 
mediately before, during, and after muscular work, this method of computing 
the energy transformations is fully applicable for purposes of comparison 
and hence can be followed implicitly in computing the results of our experi- 
ments. We have therefore used as the basis of the computations in this report 
the values given by Zuntz and Schumburg.* (See table 4.) 
Magnus-Levy, von Noorden's Handbuch der Pathologie des Stoffwechsels, Berlin, 1906, 1, p. 207. 
6 No account is taken of the cutaneous respiration which admittedly may be of considerable sixe. The in- 
fluence of the cutaneous respiration would probably affect the respiratory quotient somewhat more 
than the total katabolism. In the absence of exact knowledge regarding the r61e played by cutaneous 
respiration, we do not consider it here though doubtless in the state of profuse perspiration existing in 
many of our experiments, there must have been a greater cutaneous respiration than normal. When 
the enormous amount of carbon dioxide produced and oxygen absorbed are taken into consideration, it 
is not likely that we have greatly erred in neglecting this as yet unsatisfactorily determined factor. 
e Zuntz and Schumburg, loc. cit., p. 361, table 7. 
