
120 STORRS AGRICULTURAL EXPERIMENT STATION. 
The measurements of net income are less certain because of 
the sources of error on the physiological side to which refer- 
ence has been frequently made in these discussions. It seems 
probable that the chief of these uncertainties are those due to 
(1) the amounts of material in the alimentary canal, which 
may vary considerably from day to day at 7 A. M. when the 
experiments begin and end; (2) the possible error in assumed 
composition of protein and fats gained or lost in the body, 
though this error is probably small; and (3) the variations in 
the proportions of carbohydrates (glycogen) in the body which 
are not definitely measured in these experiments. The direct 
determination of oxygen it is hoped will help to remove this 
difficulty in future work. Meanwhile it seems safe to say that 
in the investigations here summarized the length of the experi- 
mental periods, the repetitions of the experiments with the 
same subject and with different subjects, and the number of: 
results included in the averages, give to the latter an authority 
that cannot well be disputed. It seems fair to assume, there- 
fore, that the figures for income of energy as summarized in 
Table 18 are not far from correct. 
It is probably useless to hope that the transformations of 
matter and energy in the body will ever be measured with the 
accuracy of chemical and physical processes in the laboratory, 
especially in individual experiments of short duration. Cer- 
tainty and exactitude must be sought in repeated and long- 
continued series. This statement applies to comparisons of 
income and outgo of energy. The net outgo may be meas- 
ured exactly with the respiration calorimeter, but the net 
income is influenced by physiological factors for which there is 
little hope of exact determination except with aid of ‘‘ the 
might of average figures’’ from numerous experiments. But 
with such repetitions reasonably close results can be obtained. 
It would seem that this consummation has been approached if 
not attained in the experiments with men above described. 
The agreement of the totals and averages of income and 
outgo of energy in the different classes of experiments as 
shown in Table 18 can hardly be without significance. Re- 
duced to their simplest terms, the results of these experiments 
show that the energy given off from the body in the two forms 
of heat and external muscular work equals the potential energy 
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