Temperature: Metabolic Aspects and Perception 



363 



TABLE 62. BODY TEMPERATURE AS RELATED TO AIR TEMPERATURE 

 IN A FEW SELECTED HETEROTHERMIC MAMMALS 



is poor in Echidna, better in Ornithorhynchus. Sloths, opossums, and bats 

 show some temperature fluctuation with the environment. Figure 94 gives the 

 body temperature of a Central American opossum as a function of air tempera- 

 ture; this is a nocturnal species, and the body temperature while the animal is 

 awake is consistently higher than while it is asleep, although temperature 

 changes are greatest in warm or cold air.^-" Most, perhaps all, of these hetero- 

 thermic mammals readily enter a state of cold narcosis at low air temperatures. 

 Development of Homoiothermy. Newborn mammals or recently hatched 

 birds show poor temperature regulation. A two-day-old mouse, for example, is 

 essentially a poikilothermic animal;^^^ at 10 days a mouse regulates in inter- 

 mediate air temperatures, and at 20 days in extreme temperatures. A six-day 

 rat has a body temperature 1.3-1.8 degrees above the environment over the 

 range of 24 to 37°, and 0.5 degree or less above the air at temperatures below 

 about 20°; at 12 to 16 days control occurs during activity, and at 25 days the 

 rat approaches the adult condition. ''^ Development of temperature regulation 

 may be correlated with development of myelination in nerve fibers in the 



