366 PRINCIPLES OF ANIMAL NUTRITION. 
in the more restricted sense of the ordinary functions of the internab 
organs, does not seem to be materially affected. Are we justified 
in assuming the same thing to be true in our imagined shrinkage 
of an animal? In other words, is the work of the internal organs 
proportional to the mass of the body and is the increased heat 
production in the smaller animal due to the same cause as that 
observed when an animal is exposed to a falling temperature? 
It appears quite clear that this question must be answered in 
the negative. It is a well-known fact that the circulation, respira- 
tion, and other functions are as a rule more active, in small 
than in large animals, and this greater activity must necessarily 
result in the evolution of relatively more heat. If we raise the 
temperature of the surroundings to a point corresponding to the 
critical thermal environment, we may, as we have seen, regard the 
heat production as representing: the internal work in the narrower 
sense. Rubner * reports experiments of this sort upon four guinea- 
pigs at 0° C. and at 30° C., which gave the following results for the 
production of carbon dioxide: 
CO, per Hour at 0° C. CO, per Hour at 30° C. 
Weight of 
Grms.” Per Kg. Per Square Per Kg. Per Square 
Weight, Meter Surface, Weight, Meter Surface, 
Grms. Grms. Grms. Grms. 
617 2.905 27.85 1.289 12.35 
568 3.249 30.30 1.129 10.53 
223 4.462 30.47 1.778 12.14 
206 4.738 31.56 1.961 13.16 
With the first and third of these animals direct experiment 
showed that the minimum production of carbon dioxide (critical 
point) was reached at about 30°-35°, and we may fairly assume 
this to be true of the other two. At 30°C., then, we may assume 
that the “chemical” regulation was practically eliminated and that 
the observed metabolism was that due to the work of the internal 
organs. Under these conditions, as the figures show, the metab- 
olism was still approximately proportional to the surface of the 
animal, and consequently greater per unit of weight in the smaller 
than in the larger animals. 
* Biologische Gesetze, pp. 12-18. 
