INTERNAL WORK. 359 
ism whch have already been described and which result in maintain- 
ing the rate of emission of heat at a point enough higher than before 
to provide for carrying off the extra heat arising from the physio- 
logical work of the regulative mechanism itself. In other words, 
instead of a critical temperature, we get the conception of a critical 
thermal environment, which may be reached under a variety of 
conditions, and below which we have the domain of “chemical” 
regulation, while above it is the region of “ physical” regulation. 
Influence of Size of Animal on Heat Production.—The total 
metabolism of a large animal is necessarily greater than that of a 
small one of the same species, but it is not proportional to the 
weight, being relatively greater in the smaller animal under com- 
parable conditions. 
RELATION OF Herat PropuctTion To SuRFracr.—Bergmann * 
appears to have been the first to connect the fact just stated with 
the relatively greater surface of the smaller animal, but we are in- 
debted to Rubner + for the first quantitative investigation of this 
phase of the subject. His experiments were made on six dogs 
whose weights varied from 3 to 24 kilograms each. The total 
metabolism (proteids and fat) of each of these animals in the fasting 
state was determined in from two to thirteen experiments, and 
from their results the average heat production of each animal was 
computed. The table on page 360{ shows the air temperature and 
the computed heat production per kilogram live weight in each 
experiment, and also the same corrected to the uniform tempera- 
ture of 15° C. This correction is made on the basis of Theodor’s 
experiments (see p. 351), according to which a difference of 1° 
Centigrade caused the amount of oxygen taken up by the cat to 
vary 1.11 per cent. The first series consists of a selection from 
Pettenkofer & Voit’s experiments. 
Whether we consider the observed or the corrected heat pro- 
duction we find that with the single exception of the corrected 
result for No. VI the amount per unit of live weight increases as the 
weight itself decreases. 
* Cited by Rubner. 
+ Zeit. f. Biol , 19, 535. 
{ The figures of the table are computed from those given by Rubner in 
loc. cit., p 540, and differ in some cases from the summary given in loc. cit., 
p 542. 
