INVESTIGATIONS ON METABOLISM. 95 
chamber were sufficient to convince us of their reliability. 
‘Plans are made, however, for more extended tests of this kind, 
after the introduction of changes in the apparatus which are 
intended to secure more accurate measurement and sampling 
of the air than we were able to secure with a gas meter and 
aspirators. 
PLAN AND METHOD OF EXPERIMENTS, 
In the account of experiments here given the balance of 
energy is omitted for the reason already explained, and only the 
income and outgo of matter are considered. The difficulties in 
the determination of the total water of exhalation, were not 
entirely surmounted when the experiments were made. Hence 
the amount of water in the outgo and with it the hydrogen 
balance are omitted. As the main purpose of the experiments 
was to gather experience in the manipulation of the apparatus 
and the treatment of men in the respiration chamber the de- 
termination of other elements was not attempted. Accordingly 
the factors actually determined and here reported are: 
Income:—Food, drink and their content of nitrogen, carbon, 
protein (N. x 6.25), fats (ether extract), carbo- 
hydrates (by difference), mineral matter (ash). 
Outgo:—Respiratory products; carbon dioxide and its con- 
tent of carbon. 
Feces: nitrogen, carbon, protein (N. x 6.25), fats 
(ether extract), carbohydrates (by difference), 
mineral matters (ash). 
Urine: nitrogen, carbon. 
Such experiments as these, which include measurement of 
the income of the food and drink and of the outgo of the ex- 
cretory products, including those of respiration, are commonly 
called respiration experiments. They necessitated, however, 
in each case a digestion experiment, that is to say, a compar- 
ison of the food consumed and the undigested residue which 
gives the amounts actually digested. 
DIET, MEALS.—DAILY RATIONS. 
In these experiments the effort was made to have the condi- 
tions as nearly normal as possible. T’o this end it was essential 
Piet 
1. ‘The diet be such as to agree with the subject. 
