THE UTILIZATION OF ENERGY. 525 
Respirat E : 
Quotient. and Meson; cae 
Frentzel—fat diet: 
First week ........ ccc sce eeeeaee 0.766 2.088 
Second week.........-...2.20005 0.778 2.049 
AVETARC Hee cad stleiers dais wierd is 0.773 2.066 
Frentzel—carbohydrate diet: 
First: weekiic.-c:0¢020 803 ase 0.896 1.932 
Second week.................0-. 0.880 2.031 
AVOTAZC... isb4 de iii es ag twee ee 0.889 1.980 
Frentzel—proteid diet: 
First assumption ............... 0.799 ( 1.933 
Second assumption.............. t : 1 1.824 
Reach—fat diet: 
First week; 22. cies ce gey es oe 94 0.805 2.259 
Second week.............--.-06- 0.766 2.034 
AVETA ZC. caine dae caw ewe ss 0.781 2.119 
Reach—carbohydrate diet: 
First week occ ccc giaus satu ee tare c's 0.899 2.202 
Second week............--000005 0.901 2.005 
AVOTA SCs io alent ag Bie gees 0.900 2.086 
with increasing efficiency, largely independent of the food, and the 
fact that most of the experiments with fat came later in the series 
than those with carbohydrates largely, although perhaps not en- 
tirely, accounts for the observed difference in efficiency, while the 
low figure for proteids is accounted for by the fact that these were 
among the earliest experiments. A similar effect appears in the 
experiments of Frentzel & Reach, although it is less marked, since 
walking is a more accustomed form of work than turning a crank. 
On the whole, Zuntz concludes that these experiments warrant the 
conclusion that in work production the materials metabolized in 
the body replace each other in proportion to their heats of combus- 
tion—that is, in isodynamic and not isoglycosic proportions. 
THE UTILIZATION OF METABOLIZABLE ENERGY. 
the investigations just discussed give us fairly full data as to 
the utilization of the stored-up energy of the body in the produc- 
tion of external work, and this, as we have seen (p. 497), is sub- 
stantially equivalent to a knowledge of the utilization of the net 
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