CHARACTER OF KATABOLISM 83 
Chauveau also argues that in the conversion of fat into carbohydrates 
there is a waste energy which is not utilizable for muscular work, since a part 
of the oxygen consumed must be used in first converting fat into carbo- 
hydrates, during which process there is no energy liberated which is available 
for external muscular work; hence for the same amount of muscular work 
on a carbohydrate diet there will be a considerably smaller heat production 
than when the muscular work results from fat disintegration. In opposition 
to this theory, Zuntz cites experiments made by his various students, espe- 
cially those of Frentzel and Reach a and also the experiments of Atwater, 
Sherman, and Carpenter, 6 which showed that the absorption of oxygen per 
unit of work is essentially the same whether fat or carbohydrate is burned. 
According to Zuntz, therefore, there is no selective combustion of carbohy- 
drate material during muscular activity; furthermore, since Chauveau's 
theory would require for a unit of external muscular work 30 per cent more 
energy with fat than with carbohydrates, Zuntz argues that all nutrients 
can furnish muscular energy without previous transformation into sugar. 
Respiratory Quotients of Bicycle Ergometer Experiments and their Significance. 
A comparison of the character of the katabolism before, during, and after 
work may be made either directly by comparing the respiratory quotients, 
or by comparing the amounts of protein, fat, and carbohydrates katabolized 
per minute, as computed by the Zuntz formula from the measurements of the 
nitrogen and carbon-dioxide output and the oxygen consumption. Since the 
character of the katabolism has a direct influence upon the relation between 
the carbon-dioxide excretion and the oxygen consumption, we have considered 
it unnecessary to make the elaborate computation of the amounts of glycogen 
and fat katabolized per minute, and have based all our comparisons upon the 
respiratory quotient. In doing this we have assumed that low respiratory 
quotients indicate a katabolism chiefly of fat and protein, and that the 
higher the quotient the greater the proportion of carbohydrates burned. 
It has, furthermore, been assumed that throughout the rest and work periods 
there is a relative constancy in the katabolism of protein, with no excessive 
immediate disintegration of protein as a result of the muscular activity. 
GENERAL COMPARISON OF THE RESPIRATORY QUOTIENTS. 
From an inspection of the data obtained in the bicycle ergometer ex- 
periments, it is seen that there were variations in the character of the respira- 
tory quotients obtained before, during, and after work, with no complete 
uniformity. The difficulty in considering individual experiments is clear 
when not only the variations in the amount of work done but the well-known 
influence of the preceding diet upon the character of the respiratory exchange 
are borne in mind. Furthermore, it must be remembered that in the first 
period during muscular work, the true value of the respiratory quotient may 
be affected by the formation of lactic acid, i. e., imperfect oxidation. As, 
however, the so-called lactic-acid period appears to be very transitory, its 
effect on our results has been practically ignored. 
a Frentzel and Reach, Pfluger's Archiv. 1901, 83, p. 477. 
& Atwater, Sherman, and Carpenter, U. S. Dept. Agr., Office Expt. Stas. Bui. 98, 1901. 
c Zuntz, loc. cit. 
