THE UTILIZATION OF ENERGY. 521 
Work per 
Gram, Car- 
bon Dioxide 
m,. 
No. 1—Climbing a hill pee trial) iis uierere 5 wise se 'eainiod io Hobe viewed 215.18 
18 days later .......... cece eee e eee ees 306.18 
Birsttelal 'ssiio- 4-s5 Ger oagine waaeen seme es 182.70 
2 days after first trial................... 248 .34 
10 “ ns BE NOE aah ga hati dela alee 253.74 
No. 2—Treadmill....} 12 “ ne Ee as he cantatas 238 .85 
14 “ “i RES SES [shea cvania areca anes 210.87 
15“ : Be ERs eh sida a Wie Sede 227 .04 
21 “ ie BE OTD ohae ts eet eerie crn bag 227.50 
24 months after first trial................ 441.17 
Piretitirial 4 .:¢:5i8lpiy a's avese’n sv stana.s 3. Sie vwdceng de 231.24 
No. 3—Treadmill .... ) 2 days after first trial................0.00. 231.24 
qe oi fhe ASS Faaahevanaleter ccalags a ae 286.25 
In walking the same distance (468 M.) No. 1 excreted the following 
excess of carbon dioxide over the rest value: 
Miret trial. 62 2c23sesaeniork seen aes 4.505 grams 
Ao WEEK latef yi .csd: cee aie we-oueaw ee 3.690 “ 
A month later...... bei Sa rang aia 2.780 “ 
It appears from these results that the gradual strengthening of the 
muscles during convalescence results in a more economical per- 
formance of their work, largely independent of any special training 
for a particular kind of work. It seems a justifiable conclusion, 
therefore, that a part of the gain due to training arises from its 
direct effect in strengthening the muscles, as well as from the in- 
creased skill acquired in their use. Conversely, the effect of fatigue 
in increasing the relative metabolism, as shown by Loewy,* would 
seem to be in part a direct effect. Schnyder summarizes the matter 
in the statement that it is not the work itself, but the muscular 
effort required, which determines the amount of metabolism. 
In the case of domestic animals kept chiefly for work, however, 
we may safely assume that they are constantly in a state of training, 
and that the results obtained by Zuntz and his associates on the 
horse are applicable to work done by normal animals within the 
limits of the experimental conditions. 
* Arch. ges. Physiol., 49, 405. 
