Vital Heat of Cold-blooded Animals* 153 



order to distinguish accurately the faint heat peculiar to the 

 animal among the anomalies produced by the heat continually 

 communicated to it or excited in it, by the surrounding me- 

 dium, and by the heat which it is always receiving or losing 

 by radiation. All these matters shall be explained in my Me- 

 moir, as well as the reasons which have led mo to think, that 

 the thermo-electrical apparatus is much preferable to the ther- 

 mometer, for determining the vital heat of animals with a low 

 temperature. This apparatus I have accordingly used, and I 

 have followed the same plans of experiment which I have de- 

 scribed in detail in my researches on the vital heat of vege- 

 tables. I have taken care, likewise, to prevent the cold caused 

 by evaporation, by placing the animal under observation in air 

 saturated with water. Without this precaution, I could not 

 have obtained the whole vital heat of the animal, which, in 

 many circumstances, would have been found to be even colder 

 than the surrounding air. I now proceed to give a very brief 

 notice of the results of my observation. 



Reptiles. — Different observers have estimated the proper 

 heat of the frog (Rana esculenta) Linn., from 0°.59 F. to 4°.o 

 F., (from J of a degree to 2^ degrees centesimal) above the 

 temperature of the surrounding medium. Berthold alone found 

 that this reptile, when observed in the air, was colder than 

 that medium, and when in water, it had the same tempera- 

 ture as the liquid. He found no exception to this but when 

 the frogs were copulating, when their internal heat was raised, 

 1*^.8 F. (a centesimal degree) above the temperature of the 

 water in which they were living. I have had no opportunity 

 of observing the vital heat of frogs during copulation ; I have 

 experimented on them only in a single state, and not in the sea- 

 son of their copulation. I thrust one of the needles of the th'er- 

 mometrical apparatus, sometimes into the abdomen, at other 

 times into the muscles of the thigh. In this manner I have 

 ascertained, that, in the open air, the frog is about 1°8. F. (1°.0 

 Cent.) colder than the surrounding air ; and that, when placed 

 in air saturated with water, it indicates a vital heat of from 

 0.054, to 0.09 of a degree of Fahrenheit (from 0.03 to 005 

 of a Cent, degree) above the temperature of the ambient me- 

 dium. I obtained the same result from experiments on a frog 



