514 PRINCIPLES OF ANIMAL NUTRITION. 
animal and that expended in imparting motion to the legs. The 
former portion is regarded as constant, while the latter portion 
would increase with the speed. The very close proportionality 
between the work thus computed and the total metabolism, as 
shown by the table on the preceding page, is a strong confirma- 
tion of the correctness of both methods and places the conclusion 
as to the influence of speed upon metabolism beyond reasonable 
doubt. It is to be remembered, however, that it is the total 
metabolism per kilogram and meter which increases with the speed. 
The percentage utilization of the energy, so far as the data at our 
command enable us to determine, apparently remains constant. 
Practically, however, it is the former fact which interests us, since 
the expenditure of energy in locomotion is comparable to that in 
internal work and has only an indirect economic value. A similar 
effect of speed on the metabolism in horizontal locomotion was 
observed by Zuntz* in experiments on man. In those with the dog, 
on the other hand, the variations in speed were between 64.2 and 
85.9 meters per minute, but no material difference in the metabo- 
lism due to locomotion was observed. 
In trotting, a horse expends much more energy per unit of hori- 
zontal distance than in walking. Thus, trotting at an average 
speed of 195 meters per minute (a little over 7 miles per hour), as 
compared with walking at an average speed of 90.16 meters per 
minute, gave the following results for the metabolism per kilo- 
gram mass and meter distance. 
POtHNg rast. daed naa ee eves 0.5478 cal. 
Walking i tcuaiirniaiadi seta eq ateelangalen 0.3666 “ 
On the other hand, speed is, so to speak, obtained more econom- 
ically at the trot than at the walk. In the averages just given the 
speed was increased by 116 per cent., while the metabolism was in- 
creased by only 49 per cent. The same result is reached in another 
way by computing, by means of the factor given at the beginning of 
this paragraph (0.00334 cal.), the theoretical walking speed which 
would give a metabolism equal to the average metabolism in trot- 
ting. We find this to be 147 meters per second, as compared with 195 
meters ata trot. Moreover, it was found that at the trot the metab- 
olism did not increase with the speed, within the limits of the ex- 
* Arch, ges. Physiol., 68, 198. 
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