66 
Proceedings of the Royal Society of Edinburgh. [Sess. 
VI. — The Body-Temperature of Fishes and other Marine Animals. 
By Sutherland Simpson, M.D., D.Sc. Communicated by Professor 
E. A. Schafer, F.R.S. 
(MS. received November 20, 1907. Read December 2, 1907.) 
Introduction. 
With regard to their body-temperature living beings are divided into two 
great classes, — warm-blooded animals and cold-blooded animals. This is a 
very old distinction, and although the classification is not quite accurate, 
these terms are fixed in the literature, and if not interpreted too rigorously, 
they may be conveniently used to indicate, on broad lines, what appears to 
be a fundamental difference between the two classes. Birds and mammals 
alone belong to the former division. They are called warm-blooded because 
their bodies are warm when compared with the medium in which they 
live, unless under exceptional circumstances. All other animals are cold- 
blooded, and they are so called because they have the same temperature as 
the surrounding medium, and this, to the human hand, is cold as a rule. 
However, so-called warm-blooded animals, when anaesthetised and placed 
in a cold atmosphere, may have their temperature reduced to 20° C. or 
even 15° C., and still remain alive; and, on the other hand, many cold- 
blooded animals living in the tropics may have a temperature of 38° C. or 
40° C. — Richet* observed tortoises for several days with a temperature 
over 39° C., and frogs have been known to live in water at 33° C. to 37° C. 
Obviously, therefore, it is not scientifically correct to designate a mammal 
warm-blooded with a temperature of 20° C., and a tortoise cold-blooded 
with a temperature of 39° C. 
John Hunter j- was the first to point out that the essential difference 
between the two classes lies in the fact that in birds and mammals the 
temperature is constant, and independent of that of the surroundings, 
whereas in all other animals it is inconstant, and varies with the temperature 
of the medium in which they live. To indicate this difference Bergmann J 
proposed the terms homoiothermal and poikilothermal instead of warm- 
* Richet, Did. de Physiol ., vol. iii., p. 108. 
t Hunter, Complete Works (London, 1837), vol. iii., p. 16. 
X Bergmann, Gottingen Studien , 1847, Abth. i., S. 595. 
