INTERNAL WORK. 355 
means of the so-called “ chemical” regulation, that is, by variations 
in the production of heat. 
Above this point the heat production, instead of a further de- 
crease, shows an increase, which, however, is slight as compared 
with the differences observed as a result of the “chemical” regu- 
lation. Here we are obviously in the domain of the “physical” 
regulation—the regulation by changes in the emission constant of 
the skin. This temperature at which the chemical regulation 
ceases, and which presumably varies for different species of animals, 
Ranke calls the critical temperature. Below it the regulation is 
chiefly “chemical,” above it chiefly “physical.” The slight in- 
crease in the metabolism above the critical point is plausibly ex- 
plained as due to the greater activity of the organs of circulation, 
respiration, and perspiration required for the “physical” regula- 
tion. 
Rubner’s experiments also show that the portion of the thermic 
range lying above the critical temperature falls into two distinct 
subdivisions. For a certain distance above that point, the factors 
chiefly concerned in the regulation of the body temperature are 
conduction and radiation, which keep pace with the rising tem- 
perature in the manner already explained. At the same time, 
there is a small increase in the rate of evaporation of water, approxi- 
mately equivalent to the slight increase in the metabolism above 
the critical temperature to which attention has just been called. 
Matters go on in this way through a certain range of temperature 
until the regulative capacity of the vaso-motor mechanism is 
utilized to its maximum. If the external temperature still rises, 
the emission of heat by conduction and radiation begins to decrease 
as it would in a lifeless object, and the deficit thus occasioned is 
made up by a sudden increase in the exhalation of water vapor, 
coinciding, in man, with the production of visible perspiration. 
This sudden increase in the activity of the sweat-glands is accom- 
panied, as we should expect, by an increase in the total metabolism 
and consequent heat production. 
These phenomena are well illustrated by Rubner’s experiments 
with a fasting dog, already partially cited on the opposite page. 
The following table shows the amount of heat carried off by con- 
duction and radiation and as latent heat of water-vapor at the 
