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and carbon equilibrium before the beginning of the metabolism experi- 
ment proper, and at the same time to secure a more nearly accurate 
measure of the digestibility of the food. It is almost impossible to 
obtain exact nitrogen equilibrium since physiological factors, little 
understood and not easily controlled, cause more or less fluctuation in 
the elimination of nitrogen, even when the amount in the diet is 
uniform. These preliminary digestion experiments were generally 
of 1 days' duration. Experiments Xos. 1-4, however, were both pre- 
ceded and followed by digestion periods of 3 days, while some later 
experiments were preceded by periods more or less than 1 days. In 
these preliminary digestion experiments the income and outgo of nitro- 
gen were determined, so that the nitrogen metabolism was measured, 
and in this sense they are metabolism experiments, although they are 
not here so designated. There were altogether 14 digestion and nitro- 
gen metabolism experiments which accompanied or made a part of the 
31 experiments with the respiration calorimeter. They covered 201 
days. Only a small number of the results of these digestion experi- 
ments, viz, those belonging to respiration experiments Xos. 1-1, have 
yet been published. 
Questions studied.- — Although the larger part of the seven years' 
work in connection with the respiration calorimeter in this laboratory 
has been devoted to the developing and perfecting of apparatus and 
experimental methods, yet during the progress of the inquiry a mass 
of data has accumulated and results bearing upon a variety of ques- 
tions have been obtained. A proper discussion of the results would 
include a consideration of the following and other topics: (1) The 
kinds, amounts, and digestibility of the food; (2) the quantity and 
composition of the excretory products; (3) the daily elimination of 
water, carbon dioxid, and heat, and the rates of elimination at different 
periods of the day and under different conditions; (1) the kinds and 
amounts of material actually oxidized by the different subjects under 
different conditions of rest and work; (5) the estimated amounts of 
oxygen used and the estimated respiratory quotients; (6) the demands 
of different persons for nourishment under different conditions: (7) 
the functions of the different nutrients and their mutual replacing 
power, or the nutritive values of different food materials; (8) the energy 
of the food and of the material oxidized as compared with that given 
off from the body: and. finally (9), the general bearing of the results 
upon the metabolism of energy. A number of collateral topics would 
also call for discussion, such as (10) the effects of different conditions 
of food, rest, and work upon bodily temperature; (11) the composition 
of the air in the chamber as related to the rate of ventilation and the 
well-being of the occupant, and as bearing upon the general hygiene of 
ventilation, (12) details of the apparatus, and (13) methods of experi- 
mental inquiry. 
