136 
with the two subjects the amounts for the 4 periods were, respec- 
tively, 107.2, 110.3, 55.1, and 46 grams per hour, or 33.7, 34.6, 17.3, 
and 14.4 per cent of the total. 
The parallelism between muscular work and increased water elimi- 
nation by the lungs and skin is not close, nor does the increase coin- 
cide at all with the period of work. The a lag*' in elimination of 
water, i. e., the length of time between its ingestion in food and drink 
or its formation by the oxidation of hydrogen on the one hand and its 
elimination by various channels on the other is decided by factors too 
complex for full discussion here, and must be discussed in the light of 
later experiments. 
ELIMINATION OF CARBON DIOXID. 
The carbon dioxid given off from the body is derived from the oxi- 
dation of the carbon of the food and body material, and hence serves 
as a measure of the amount of that oxidation. The quantity given off 
in the urine and feces is very small indeed. It is here neglected, and 
that given off b} T the lungs and skin is taken as representing the total 
elimination. The quantity eliminated in a given period depends 
upon a variety of conditions, among which are (1) the character of the 
diet and the time which has elapsed since the last meal was taken. (2) 
the muscular activity of the subject — whether at rest or at work, (3) 
the external temperature, (4) the age and body weight, and (5) indi- 
vidual peculiarities of the subject. The accuracy with which the car- 
bon dioxid eliminated for a given period measures the production for 
that period depends upon the so-called wt lag" in the elimination, a 
topic to be discussed in another place. 
In the experiments here reported there are considerable fluctuations 
in the output. Of the factors which cause these fluctuations, the 
most important is the muscular activity. The differences in the food 
were mainly those called for by the differences in the muscular exer- 
cise. The external temperature, i. e., that of the air in the chamber, 
was kept as nearly 20° C. as convenient. The subjects were young, 
healthy, active men, of similar age, height, and weight, but differing 
slightly in the amounts of food to which they were accustomed, so 
that there was nothing to imply differences in personal characteristics 
so great as to affect materially the oxidation of carbon. 
The figures for the daily elimination of carbon dioxid are summa- 
rized in Table 147, which shows the average amount per hour during 
each period and for the whole day and the percentage which the out- 
put for each period makes of the average amount for twenty-four 
hours. • 
