82 MUSCULAR WORK 
as the most mobile of the nutrients circulating with the blood, they can be 
more quickly brought to the place where they are to be used. He further 
states that he and his co-workers have never observed so high a respiratory 
quotient as Chauveau found between the 40th and 45th minute of the ex- 
periment except when, on account of fatigue, the circulation and respiration 
failed to furnish an adequate supply of oxygen to the active tissues; he 
therefore infers that under those conditions the high quotient is due to a kind 
of anaerobic action of the muscles similar to that observed in dogs by Pfliiger. 
The clearest expression of the views of the Zuntz school on the character 
of the katabolism during muscular work may be obtained from a recent article 
by Zuntz. a Here Zuntz points out the fact that the best evidence of the nature 
of the material burned in the muscles during muscular work is secured in 
experiments in which the work, which should not be too great, is carried out 
over a long period of time without excessive fatigue. Such experiments were 
made, he claims, by himself and Hagemann on horses and by Katzenstein 
and others of the Zuntz school on men. In these experiments the respiratory 
quotient in the work-period was in many cases exactly equal to that during 
rest, and in others a few units lower, namely, in long-continued experimenting. 
In one of Katzenstein's experiments, for example, the resting quotient was 
0.80; when the subject walked about on horizontal ground and even walked 
up an incline, the quotient remained the same, although the oxygen consump- 
tion was increased to more than 5 times that of normal. In experiments 
with soldiers, in which marching followed a rest-period, Zuntz and Schum- 
burg b also found equal respiratory quotients for rest and work. If the 
march was very fatiguing, they always found a respiratory quotient 6 units 
lower than at the beginning of the marching. To explain the lower quotients 
after excessive work, Zuntz cites some experiments by himself and Hagemann 
on a horse in which the respiratory quotient during rest, shortly after feeding 
with carbohydrate-rich food, was always near 1, while with work there was 
a tendency toward a lower respiratory quotient. 
While Chauveau's experiments are comparable with those reported 
in our research since they were made in the post-absorptive condition, the 
experiments of Zuntz and Hagemann with a horse were always made with 
food, and consequently the situation was complicated by the continual ab- 
sorption of the nutritive materials out of the alimentary tract. Zuntz, in 
computing the consumption of material by the horse, in at least one ex- 
periment indicates that the material used for the muscular work was in 
very large part fat, although the horse certainly had not drawn upon 
more than one-fourth of its glycogen supply. In one experiment, in which 
the animal worked for 95 minutes, the energy was in large part derived from 
the combustion of glycogen, the respiratory quotient being 0.91. During 
subsequent work of 27 minutes the quotient found was 0.81, indicating that 
the energy was in large part derived from the combustion of fat. In the first 
period, therefore, four times as much glycogen was used as fat, while in the 
last period only one-seventeenth of the total energy came from glycogen. 
Zuntz maintains that the experiments on men made by his students lead to 
the same conclusion, citing especiall y the experiments of Heinemann. 6 
■ Zuntz, in Oppenheimer's Handbuch der Biochemie, Jena, 1911, 4, (1), pp. 849-850. 
b Zuntz and Schumburg, Physiologie des Marsches, Berlin, 1901. 
c Heinemann, Pflttger's Archiv f. d. ges. Physiologie, 1901, 83, p. 441. 
