INTERNAL WORK. 367 
Strong confirmation of this conclusion is afforded by the exper- 
iments previously cited. In many of them, notably in Rubner’s, 
the range of size is so great that to regard the differences in heat 
production as arising from a direct stimulation of the metab- 
, olism, as in the case of a fall in the external temperature, leads 
to improbable consequences. Thus a comparison of the largest 
with the smallest dog in Rubner’s experiments (p. 361) shows 
that if we regard the heat production of’ the former as represent- 
ing simply the work of the internal organs, over 56 per cent. of the 
heat production of the smaller animal must, on the supposition 
that the internal work is proportional to the mass of the body, have 
arisen from some other source. Such an enormous increase in the 
metabolism of the body simply for the sake of heat production 
can hardly be regarded as probable. Still further, if we assume 
(compare p. 354) a temperature of about 20° C. to represent the 
critical point for the dog, then, on the hypothesis that the necessary 
internal work per unit of weight is the same, we find that a fall of one 
degree in temperature must have produced about six times the 
effect upon the metabolism of the smallest dog that it did on that 
of the largest one, while if we take the other alternative and seek to 
explain the results on the assumption of a higher critical tempera- 
ture for the smallest dog, we find for the latter about 364° C. 
Taking these considerations along with the results of Rubner’s 
trials with the four guinea-pigs, it seems most reasonable to assume, 
in default of more extensive investigations directed to this specific 
point, that the critical temperature is substantially the same for 
large and small animals of the same species and that the work of 
the internal organs is approximately proportional to the surface 
of the animal. . 
Substantially the same conclusion has been reached by v. Héss- 
lin * from a quite different point of view. He points out that the 
increased production of heat below the critical temperature is not 
proportional to the difference in temperature between the body and 
its surroundings, as it should be, according to Newton’s law, if the 
emission constant of the surface remained the same. Taking as an 
example Theodor’s experiments (p. 351) he makes the following 
comparisons: 
. * Arch. f. (Anat. u.) Physiol., 1888, p. 323. 
