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HEAT REGULATION’ IN ANIMALS. 929
The Action of the External Temperature also stands in close relation
to muscular work, namely to the question as to whether the chemical
heat regulation is independent of the muscular activity. The heat
regulation, as is well known, is of two kinds, namely the chemical heat
regulation, which consists in a change in the metabolism and which man-
ifests itself as an increased heat production due to the increased metabo-
lism at low temperatures, and the physical heat regulation, which occurs
generally at higher temperatures and is caused by changes in the con-
ditions in the heat elimination of the thermal equilibrium.
In regard to the chemical heat regulation, which will only be discussed
here, we must differentiate between cold-blooded and warm-blooded
animals. In the first the metabolism rises with an increase in the surround-
ing temperature, while in the second group the conditions are different.
The experiments of Speck, Loewy and Johansson j
on human beings
have shown that the lowering of the external temperature is without
influence upon the extent of metabolism (measured by the gas exchange)
only as long as all natural and non-voluntary movements of the muscles
are excluded; otherwise the metabolism is raised. A chemical heat regu-
lation, i.e., a rise in metabolism without noticeable movements of the
muscles, is not accepted in man, or at least it has not been proven. The
heat regulation, in man, at lower temperatures seems to be brought about
by the natural or reflex production of muscle action, nor has a chemical
heat regulation in the reverse sense, namely, a fall in the catabolism by
raising the external temperature, been shown in man. The investigations
of Eykman 2
upon inhabitants of the tropics also show the same result,
namely, that in human beings no appreciable chemical heat regulation
occurs.
In animals the conditions are different so far as that a chemical heat
regulation in the true sense has been positively shown. The investiga-
tions of Rubner 3
on various animals have shown that the reduction
of the external temperature with these, causes a considerable chemical
heat regulation by increasing the metabolism without any chill or shiver
movements. On sufficient cooling the temperature of the body may fall
irrespective of the increased metabolism, and at a certain limit of body
temperature the exchange of material becomes still lower with decreasing
temperature. According to Rubner many animals can bear a temperature
of 0° C. for days in absolute rest. If the natural muscular activity is
eliminated by poisoning with curare or by section of the spinal cord, then,
as shown by Pfluger 4
and his pupils, the warm-blooded animal behaves
1
Speck, 1. c; Loewy, Pfliiger’s Arch., 46; Johansson, Skand. Arch. f. Physiol., 7.
2
Virchow’s Arch., 133, and Pfluger’s Arch., 64.
’ Arch. f. Hyg., 37, and Handbuch d. Hyg., Bd. 1, Leipzig, 1911.
4
See footnote 2, page 591.
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