JO HANSEN 



Robinson (1954) studied the development of the mechanisms 

 for evaporative heat loss in Australian marsupials. She found a 

 close correlation with structural evolutionary trends. She recorded 

 breathing rate, pulse rate, evaporative weight loss, and she also 

 studied sweat patterns. There is a great amount of evaporation 

 from the respiratory tract and additional evaporation from the 

 buccal mucosa during open-mouthed panting. Sweat glands were 

 easily located over the entire body surface (Bolliger and Hardy, 

 1945). The sweat glands are, however, of a primitive apocrine type 

 and of seemingly little importance as evaporative mechanisms. 

 Evaporation is, on the other hand, significantly aided by salivation 

 and coat licking. Robinson concludes that the heat tolerance in the 

 Australian marsupials studied followed the ascending order of phylo- 

 genetic development, for instance, the primitive bandicoot (Peram- 

 eles n acuta ) , next the opossum (Trichosurus caninus ), then the 

 cuscus ( Spilocuscus nudicaudatus) , the koala ( Phascolarctos cine- 

 reus), the wallaby ( Petrogale penicillata ) , and most superior, the 

 wallaroo ( Mac r opus robustus). 



Higginbotham and Koan, in 1955, studied temperature regula- 

 tion at elevated air temperatures in the Virginia opossum ( Didelphis 

 virginiana) . They found that when body temperature increased to 

 about 38 C, panting, profuse salivation, and licking of saliva upon 

 feet and tail and parts of the trunk, was common. They monitored 

 anaesthesia to a point where panting and salivation still persisted, 

 but coat licking, of course, was abolished. This fact prevented the 

 animal from keeping the body temperature at sub- lethal levels, 

 and they conclude thatthe spreading of saliva upon the body surfaces 

 and subsequent evaporation constitutes an indispensable mechanism 

 for heat dissipation. Robinson and Morrison (19 57) studied the reac- 

 tions to hot atmospheres of various species of Australian marsu- 

 pials and placental mammals. Their material covers as many as 

 25 species of Australian marsupials, plus 4 indigenous Australian 

 rodents. They make the very interesting and, in my mind, important 

 comparisons of temperature response to activity in some of their 

 subjects. In members of the Dasyuridae, rises of 4 C were not 

 uncommon. They report that maintenance of body temperature at a 



constant but higher than normal value was successfully achieved by 



° o o 



all their animals at air temperatures of 35 C. At 40 C air tem- 

 peratures, some species failed to adjust to a steady state condition. 



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