EXPERIMENTS ON METABOLISM OF ENERGY. PLO 
a number of investigators have served a useful purpose, but 
they will doubtless have to be modified as the fundamental 
data become more exact and numerous. 
One principle which thus far has not received adequate recog- 
nition in dietary standards may perhaps be expressed by saying 
that the standards must vary, not only with the conditions of 
activity and environment, but also with the nutritive plane at 
which the body is to be maintained. A man may live and 
work and maintain bodily equilibrium on either a higher or 
lower nitrogen level or energy level. One essential question 
is: What level is most advantageous? The answer to this 
must be sought, not simply in metabolism experiments and 
dietary studies, but also in broader observations regarding 
bodily and mental efficiency, and general health, strength, 
and welfare. 
ELIMINATION OF WATER. 
The water taken into the body in the food and drink and 
formed by the oxidation of hydrogen is excreted by the kidneys, 
lungs, and skin. The amount eliminated by the kidneys varies 
with the amounts taken in the food and drink and eliminated 
in the respiration and perspiration, and is, in consequence, very 
irregular. The amount of water given off by the lungs and 
skin appears to depend largely upon the muscular activity of 
the subject and the temperature of the surrounding air, and to 
be less affected by the income in food and drink. 
Income and outgo of water per day.—'Table 25 recapitulates 
the figures for the average amounts of water taken in the food 
and drink and eliminated in the various excretions in the seven- 
teen experiments previously enumerated. In all these experi- 
ments the days were divided into six-hour periods. 
It is to be remembered that there was considerable milk in 
the daily diet and this is reckoned as food rather than drink. 
How the amounts of water in food and drink in these experi- 
ments would compare with those in the average diet in general 
it is impossible to say for lack of sufficient data. ‘The average 
daily amount of water in food and drink together in the rest 
experiments was for E. O. 2,538 grams, for A. W. S. 2,275, 
and for J. F. S. 1,888 grams. In the work experiments with 
HO. it wasie.7 71 gtams.and with Je. S. 2,225 grams. 
