INTERNAL WORK. 351 
of water thus supplied to the surface of the skin is a powerful means 
of refrigeration, as we know no less from common experience than 
from scientific determinations, the evaporation of a single gram of 
water requiring approximately 0.592 Cal. of heat. With very 
high temperatures, especially in a humid atmosphere, however, 
even this method of disposing of the heat becomes insufficient and 
the extreme upper limit of the thermal range is passed. 
These two methods of regulation of the body temperature are 
often spoken of collectively as “ physical” regulation. 
Variations in Amount of Heat Produced.—Just as there is a 
superior limit beypnd which the regulation of the body tempera- 
ture by the means above described cannot he carried, so it is obvious 
that there must be a lower limit of regulation. However much the 
cutaneous circulation may be reduced, the skin will always lose heat 
to a sufficiently cold environment faster than it is being generated 
by the internal work of the body. Under these circumstances the 
only method by which the temperature of the animal can be main- 
tained is an increase in the rate of generation of heat. 
That changes of external temperature affect the amount of heat. 
generated was shown by the experiments of Lavoisier and the 
observations of Liebig, but Liebermeister * appears to have been 
the first to clearly enunciate the theory of regulation by variations 
in the rate of production. The fact of such regulation has been 
fully demonstrated by numerous subsequent investigators. As a 
typical example we may take the well-known experiments of Theo- 
dor ¢ on a cat, some of the results of which are as follows: 
Temperature, |CarbonDioxide Oxygen Temperature, CarbouDioxide, Oxygen 
eg. Excreted, Taken Up, Deg. Excreted, Taken Up, 
Cent. Grms. Grms. Cent. Grms. Grms. 
—5.5 19.83 17.48 12.3 17.63 17.71 
—3.0 18.42 18.26 16.3 15.73 14.74 
0.2 18.24 19.95 20.1 14.34 12.78 
5.0 17.90 14.82 29.6 13.12 10.87 
Numerous other investigators have obtained similar results, 
but the effect of low temperature in stimulating the heat produc- 
tion of warm-blooded animals is too well established to require an 
* Arch f. (Anat. u.) Physiol., 1860, pp. 520 and 589; 1861, p. 661. 
} Zeit. f. Biol., 14, 51. 
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