INFLUENCE OF MUSCULAR EXERTION UPON METABOLISM. 211 
Errects ARE IymmepratTe.—Experiments like those of Petten- 
kofer & Voit, extending over twenty-four hours, give simply the 
total effect. of the performance of work upon the carbon balance. 
' By the use of the Zuntz type of apparatus, however, it is possible 
to follow the gaseous exchange in its details through successive 
short periods as well as to determine the amount of oxygen con- 
sumed. The data thus obtained give a clear picture of the imme- 
diate effects of work upon metabolism and have led to the extensive 
use of this type of apparatus in experiments of this nature. The 
results of these experiments agree with common experience in 
showing that these effects appear very promptly and soon reach 
their maximum, disappearing as promptly after the work ceases. 
In other words, the increase in the carbon metabolism is very 
closely confined to the time during which the work is actually 
performed. 
The Respiratory Quotient.—The ratio between carbon dioxide 
produced and oxygen consumed, commonly known as the respira- 
tory quotient, as has been pointed out in Chapter III, enables us 
to form a fairly clear idea as to the general nature of the total mate- 
rial metabolized, and hence much study has been bestowed upon 
the relation between these two quantities. 
Is VariaABLE.—We have already seen that the respiratory quo- 
tient may vary considerably during repose, being largely deter- 
mined by the nature of the food. The same thing is true of the 
respiratory quotient during work. 
Zuntz,* in experiments on a fasting dog, obtained the follow- 
ing values for this quotient: 
Number of Average 
Experi- Respiratory 
ments. Quotient. 
Rest: Standing tess 2 0.69 
(OLY os sre even ss oe weet sane es Be 6 0.71 
Horizontal locomotion ............... : 8 0.73 
Locomotion up hill.................. : 5 0.77 
Horizontal draft ............2-2 2 ee eee a 10 0.77 
In Zuntz & Hagemann’s + experiments upon the horse the respi- 
ratory quotient in the single work periods ranged from 0.729 upon a 
* Arch. ges. Physiol., 68, 191. 
} Landw. Jahrb., 27, Supp. ITI, 296-331. 
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