352 



Comparative Animal Physiology 



metabolic heat results in some evaporation. Visceral temperature is never as 

 much as 0.1° C. above surface temperature; it approaches wet-bulb tempera- 

 ture (Fig. 87). In unsaturated air the evaporative heat loss exceeds the metab- 

 olic heat gain, and the body is cooled (Fig. 87). In Bufo at 27.6° C. and 

 relative humiditv (R.H.) of 82 per cent, the body temperature was 26.5°; at 



Fig. 87. The internal temperature ot frogs exposed to air moving at different speeds. 

 Data are given in relation to the wet-bulb temperature (W. B.); dry-bulb temperature 

 (D. B.). From Mellanby.'^ 



the same temperature, with relative humidity of 27 per cent, the body tempera- 

 ture was 17.5°.'-'' In dry air so much heat is lost by vaporization that heat can 

 be gained Irom the air by conduction.'* The metabolism of an amphibian 

 calculated for 37° is only one-fifth that of a mammal (mouse) of comparable 

 size.'" At 20° a frog produced CO^ equivalent to 6 cal./hr. but hourly lost 



