IX. ANIMAL HEAT. 



A. BODILY TEMPERATURE. 



Homothermous and Poikilothermous Animals. Animal organisms are 

 divided as regards bodily temperature into two classes, homothermous and 

 poikilothermous. The temperature of homothermous (warm-blooded) animals 

 is constant within narrow limits and is not materially affected by alterations 

 of the temperature of the medium in which the organism lives. The tempera- 

 ture of poikilothermous (cold-blooded) animals normally ranges from a frac- 

 tion of a degree to several degrees above that of the surrounding medium, and 

 under ordinary circumstances rises and falls with corresponding changes of sur- 

 rounding temperature. The old terms warm-blooded and cold-blooded imply 

 that the difference between the two classes is one of absolute temperature, the 

 former having a temperature higher than the latter, and although this is gener- 

 ally the case it is not necessarily so. For instance, Landois has recorded that a 

 frog (cold-blooded) in water at a temperature of 20.6 C. had a temperature of 

 about 20.7 C., and that when the water was at 41 C. his temperature rose to 

 about 38 C., which is higher than the mean temperature of man (warm- 

 blooded). The temperature of cold-blooded animals may, therefore, be higher 

 than that of warm-blooded animals. The difference therefore is relative and 

 not absolute, the chief distinguishing feature being that the temperature of 

 homothermous animals is practically constant, while that of poikilothermous 

 animals fluctuates with the temperature of the medium in which the organism 

 exists. The class of homothermous animals includes mammals and birds ; and 

 that of poikilothermous animals, fish, reptiles, amphibia, and invertebrates. 



Temperatures of Different Species of Animals. The temperature of 

 every animal varies in different parts of the organism, so that in making com- 

 parisons it is necessary that the observations be made in the same region of the 

 body of the different individuals, and as far as possible under the same internal 

 and external conditions. As a rule, rectal temperatures are preferable, and 

 in making them it is especially desirable, in order to ensure practical accuracy, 

 that the bulb of the thermometer be inserted well into the pelvis, and that it 

 does not rest within a mass of fecal matter. The depth to which the bulb is 

 inserted is also of importance, as shown by Finkler, who found in experiments 

 on a guinea-pig that the temperature was 36.1 C. at a depth of 2.5 centimeters, 

 38.7 C. at 6 centimeters, and 38.9 C. at 9 centimeters. The following records 

 of mean bodily temperature of various species have been derived from various 

 sources, chiefly from the compilations of Gavarret : 



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