JO HANSEN 



Let us next look at the physiological responses to high air tem- 

 peratures in the armadillo. Figure 18 shows the changes in rectal 

 and skin temperatures and oxygen consumption when the ambient 

 temperature was increased above 30 G. The relative humidity was 

 kept below 30%. As the air temperature was increased in steps to 

 42 C over 4 to 5 hours, the rectal temperature rose to 40 C. If 

 the air temperature was increased from 30 Gto 42 C in one step, 

 the rectal temperature reached 40 C in less than 3 hours. From 



the behavior of the animals, 40 C seems near the upper lethal 



o 

 limit for the rectal temperature, although 41.5 C was repeatedly 



tolerated for periods of less than 1 hour. The skin temperature on 

 the back armor rose markedly in a step- wise fashion following the 

 changes in room temperature. The skin remained completely dry, 

 however, and no active sweat glands were detected with either of 

 the two methods used. The circulation to the skin was greatly aug- 

 mented; even the dorsal armor blushed pinkish red. The ears were 

 markedly vasodilated, constantly vibrating. At high air temperature 

 panting is an important avenue of heat loss for the armadillo. The 

 respiratory rate rose from 30 to 40 breaths a minute to almost 200 

 a minute. The g-reatest increase in rate seemed to occur when the 



° 



rectal temperature was between 37 C and 28 C (Fig. 19). During 

 panting the nostrils were red and vibrating intensely. There seemed 

 also to be a rather profuse salivation from the buccal mucosa. How- 

 ever, no licking ever occurred. The oxygen consumption rose from 

 about 240 cc/(kilo x hr) to 400 cc/(kilo x hr). Part of this increase 

 was related to the muscular activity of hyperventilation, part to 

 the elevated rectal temperature. The significance of panting in the 

 armadillo's response to heat was demonstrated by anesthetizing 

 an animal when its body temperature was about 38 C and the air 

 temperature was 40 G (Fig. 19). As soon as the respiratory rate 

 was depressed to normal or subnormal levels, the rectal tempera- 

 ture rose sharply. During exposure to the hot environment, the 

 animals usually turned on their sides immediately, stretching their 

 front legs forward and their hind legs backward so that their ven- 

 tral surface was maximally exposed. When the rectal temperature 

 was 40 G, the animals were obviously uncomfortable and some 

 attempted to escape. 



120 



