THE UTILIZATION OF ENERGY. 525 ° 
Respiratory Energy per Kg. 
Quotient. and Meter, cals. 
Frentzel—fat diet: 
First week s¢ <.:0s'ss abess tessa Gos 0.766 2.088 
Second week.................45- 0.778 2.049 
AVETARE sicie) 5 sda d caters weno elas 0.773 2.066 
Frentzel—carbohydrate diet: 
First: week ies asis:s 3 sews 9 hess 300 0.896 1.932 
Second week...............0005 0.880 2.031 
AVOTARC es Sinaia owas Aveeno ae 0.889 1.980 
Frentzel—proteid diet: 
First assumption ............... 0.799 1.933 
Second assumption.............. ' . 1.824 
Reach—fat diet: 
Hirst -week.....o.css0s.ecsace snares 4 ciclo 5 0.805 2.259 
Second week............0000000 0.766 2.034 
AVETAPC ss io coca aenom sagt 0.781 2.119 
Reach—carbohydrate diet: 
First week ............000e ce uee 0.899 2.202 
Second week................0055 0.901 2.005 
AV OETARC oosaasdia gues sv aiere vw apes 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. 
she 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 
