CHARACTER OF KATABOLISM 77 
derance of fat, it has been found that there was a material alteration in the 
respiratory quotient indicating a difference in the character of the material 
burned under the varying conditions of diet. The respiratory quotients with 
a carbohydrate-rich diet, even 12 hours after the last meal, were invariably 
higher than those after a carbohydrate-poor diet, while with a carbohydrate- 
free diet the respiratory quotient quickly reached 0.7 or even below, indicat- 
ing a combustion almost exclusively of fat. The marked and immediate 
influence on the respiratory quotient of the absence of carbohydrates from the 
food accentuates the fundamental importance of determining the post-absorp- 
tive value of the respiratory quotient in the normal resting position before 
every experiment in which the influence of a superimposed factor, such as 
muscular work, is to be studied. 
The Normal Resting Metabolism as Determined in this Research. 
As has already been explained, it has not been necessary to assume a 
basal metabolism in this research, since the normal resting metabolism for 
each individual day was established by a preliminary rest experiment each 
morning. While this of course largely increased the number of experiments, 
the resting values thus obtained had an added interest in that they showed 
what degree of constancy may be expected from day to day and throughout 
5 months in the gaseous exchange of a normal resting man in the post-absorp- 
tive state. 
Naturally, the greatest number of rest experiments were made with the 
professional bicyclist, M. A. M. In table 91 are given in abstract the results 
for the series of experiments made with this man beginning December 7, 1911, 
and ending with April 16, 1912, each experiment usually consisting of three 
periods of 15 minutes each. During the winter there was a slight progressive 
change in body-weight from 64.5 to 68 kilograms, hence the results have been 
computed per kilogram of body-weight per minute. The data given repre- 
sent the fluctuations that may be fairly expected to occur in the course of a 
season of experimenting with a subject of this type. As has been previously 
stated, the man was an ideal subject and became thoroughly used to the 
apparatus, adjusting himself in every way to the experiments without the 
least hesitancy or disinclination. 
The carbon-dioxide production per kilogram per minute varied from 
2.86 to 3.49 c.c. with an average of 3.12 c.c. per kilogram of body-weight 
per minute. Since we know that the amount of carbon dioxide produced 
fluctuates considerably with the character of the preceding diet and with the 
storage of body-material, these fluctuations are no greater than one would 
normally expect to find. 
The oxygen consumption varied from 3.38 to 4.09 c.c, averaging 3.67 c.c. 
per kilogram of body-weight. The measurement of the oxygen consump- 
tion represents much more nearly the calorific production than does the 
carbon-dioxide excretion, and hence we have in the oxygen consumption 
a more accurate index of the total heat production. This, it is seen, amounts 
to an extreme variation of 7 parts in 34, or essentially 20 per cent, so that 
without attempting to analyze the results for each individual day, it can be 
seen that the resting metabolism, even when obtained under ideal conditions, 
may vary 20 per cent in the course of a winter. A close examination of the 
