146 
The conservation of energy in'the body. —If the law of the conserva- 
tion of energy obtains in the living organism, the net income and the 
net outgo of energy should be the same. In such physiological experi- 
menting, however, it would be hardly fair to expect the figures for the 
two to agree for each day of a given experiment or for each experiment 
as a whole, even if the measurements with the respiration and bomb 
calorimeters are exact. There may be errors in the estimates of the 
amounts and heats of combustion of the materials actually oxidized. 
Variations due to irregularities of the physiological processes of the 
body are unavoidable and may materially affect the results. For 
instance, the calculations assume that the quantities of material in the 
alimentary canal and of carbohydrates in the body as a whole are the 
same at the end as at the beginning of each day or experiment, whereas 
they may differ considerably, and the differences would materially 
affect the results. But it might be hoped that, if the methods are 
correct, these errors would tend to counterbalance one another in a 
series of experiments, and that, in the average of a sufficiently large 
number, the errors would thus be eliminated, so that the income and 
outgo would be very nearly the same. 
Exactly this is the case in the data here reported. The variations 
for individual days, and even those for the individual experiments, as 
shown in the detailed tables in this and the previous bulletins, are not 
inconsiderable, but in the average of all the experiments the agree- 
ment is very close. Thus, in the 33 days of the 9 rest experiments 
with E. O. , according to the figures for the individual days the net 
outgo varies from 165 calories below to 194 calories above the net 
income. Expressed in percentages of net income, the range here is 
from —6.5 to +9.1 per cent. Both these extremes occurred on the 
first days of the respective experiments. In general, the results for 
the first day of an experiment are found to be less satisfactory than 
those for the succeeding da3 T s. Considering each experiment as a 
whole, and comparing the averages of the several experiments one 
with another, the range of variation is less. Here the net outgo varies 
from 103 calories below to 62 calories above the net outgo per day. 
Expressed in percentages of net income, the range is from —4.1 to 
+2.9 per cent. But in the average for the 9 experiments the figures 
for the net income and outgo are practically the same, being 2,288 and 
2,278 calories, respectively. In the average of the 2 da}^s of the rest 
experiment with A. W. S. there is a disparity of 1.1 per cent, and in 
the average of the 9 days of the 3 rest experiments with J. F. S. the 
difference is 0.9 per cent. Taking the 45 days of the 13 rest experi- 
ments together, the average income is 2,255 and the average outgo 
2,250 calories; the difference is 0.2 per cent. In the average of the 
8 days of the 2 work experiments with E. O. the net income and 
outgo are 3,865 and 3,829 calories, respectively, the difference being 
