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 37.2 2.151 10 38.6 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 1.273 
40.0 39.5 1.454 
A later experiment by Rubner ¢ upon a dog, in which the heat 
production was measured by a calorimeter, gave the following 
results: 
Temperature of Air. Heat Production per Kg. 
COSC Ss enor os Suhel tsar tal Gel, 83.5 Cals. 
DOO ate non een araese ad Ben aaa aaa ae 63.0 “ 
20 20? 6% esse sia ele yes aeeoien a tun a kacae ie Gite 53.5 
25 0 eer Ree ey a ae aaa 54,2 
BONOP orca des a aioe cel, Ga eke 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. 
7 Archiv f. Hygiene, 11, 285. 
t Rubner (Biol. Gesetze, p. 30) says that for naked man it is about 37° C. 
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