CHARACTER OF KATABOLISM 95 
cated in the majority of experiments by the respiratory quotient before work. 
If the combustion during severe muscular work were exclusively of carbo- 
hydrates, with the amount of katabolism here involved very high respiratory 
quotients would be expected; yet, on reference to table 92, it is seen that the 
respiratory quotients during severe muscular work average only 0.88 for 
34 days, with a respiratory quotient for the initial base-line of resting metab- 
olism of 0.85. Porges, by cutting the liver out of the circulation, found that 
a respiratory quotient which was essentially that of fat katabolism before 
the experiment, rose immediately afterwards, his results pointing strongly 
toward an exclusive combustion of carbohydrates, and the experiment made 
by Verzar in Tangl's laboratory b gave somewhat the same results. We are, 
however, disinclined to cite these researches in support of the belief that 
muscular work is done exclusively by the combustion of carbohydrates, for 
we agree fully with Zuntz c that respiration experiments made under these 
abnormal conditions do not warrant such sweeping deductions. 
Out final conclusion must be, therefore, that the more severe the mus- 
cular activity, the heavier is the draft upon the carbohydrate material in 
the body, with a consequent persistent alteration in the character of the 
katabolism, the proportion of carbohydrate burned being increased during 
the muscular- work period. As the work progresses, and the subject is still 
without food, the drafts upon the carbohydrate storage in the body become so 
extensive that, after the cessation of the work and the "specific working 
katabolism" disappears, the katabolism of the body is such that a much 
lower proportion of carbohydrates is burned for the total energy output of 
the resting period. The average results of the experiments in this research, 
although they suggest such a conclusion, do not demonstrate absolutely 
that muscular work is done exclusively at the expense of carbohydrate 
combustion. 
While basing the interpretation of our results upon the depletion of 
carbohydrate storage and the changing of the character of the katabolism 
from carbohydrate-rich to carbohydrate-poor after work, an alternative 
explanation is possible. If we assume, what as yet unfortunately lacks 
conclusive experimental demonstration, that fat is converted in the body to 
carbohydrate, certain of our values, particularly those in the first periods 
after work and below 0.7, strongly suggest this explanation. 
Similarly a further assumption might be made that the respiratory 
quotient after work is really compounded of two or more metabolic phases, 
so that to assess properly the values which we obtained we should subtract 
the basal output of carbon dioxide and intake of oxygen, i. e., the output and 
intake obtaining before work is started, from the output and intake which are 
found after work has ceased. This would give us what might be termed 
the normal basal metabolism obtaining in the periods both before and after 
work. The respiratory quotient computed from the excess of oxygen in- 
take and carbon-dioxide output over the basal metabolism might be con- 
sidered as representing the changes which take place as the direct result of 
the work done. If such calculations be made extraordinarily low respiratory 
quotients are found. 
a Poiges, Biochem. Zsitschr, 1910, 17. p. 131. * Vers&r, Biochem. Zeitschr., 1911, 34. p. 52. 
e Zuntz in Oppenheimer - a Handbuch der Biochemie des Menachen und der Tiere, Jena, 1911, 4, (1), p. 855. 
