354 PRINCIPLES OF ANIMAL NUTRITION. 
Later and more comprehensive experiments with animals by 
Rubner have given corresponding results. Thus with two guinea- 
pigs the following figures were obtained in 24-hour experi- 
ments: * 
Mature Animal. Young Animal, 
Temperature | Temperature | CO, per Kg. ||Temperature | Temperature | CO, per Kg. 
of Air, of Animal, and Hour, of Air, of Animal, and Hour, 
Deg. C. Deg. C. Grms. Deg. C. Deg. C. Grms. 
0 37.0 2.905 0 38.7 4.500 
11.1 87.2 2.151 10 - 88.6 3.433 
20.8 37.4 1.766 \ 20 38.6 2.283 
25.7 37.0 1.540 30 38.7 1.778 
30.3 37.7 1.317 35 39.2 2.266 
34.9 38.2 | = 1.278 : : 
40.0 39.5 1.454 
A later experiment by Rubner f upon a dog, in which the heat 
production was measured by a calorimeter, gave the following 
results: 
Temperature of Air. Heat Production per Kg. 
Gi OP Oh tras oasis armors, wade ae 83.5 Cals. 
DR BOE sais canis ow eeers tocde-s alte h! ale eines 63.0 “ 
DOO? earesiaace ae saah cienahs Ga acseedhatecd 53.5 “ 
Der a arestea os ciit ie nletaba sean cael 4 euksaieess 54.2 “ 
OO SOF Riese Oe alias ewe aang a ees 56.2 “ 
The uniform testimony of these various experiments is that for 
each species there is a certain external temperature at which the 
metabolism and consequent heat production reach a minimum. 
With man in ordinary clothing it would appear to lie at about 
15° C.,f with the dog at about 20° C., and with the guinea-pig at 
about 30°-35° C. Below this point the heat production rises or 
falls with changes of external temperature; or, in other words, the 
constancy of the body temperature is secured, in part at least, by 
* Biologische Gesetze, p. 13. 
+ Archiv f. Hygiene, 11, 285. 
t Rubner (Biol. Gesetze, p. 30) says that for naked man it is about 37° C. 
