EVOLUTIONARY ASPECTS IN MAMMALS 



within the range of the deep body temperature. The foot and tail 

 were, however, held at levels below the core and the environment 

 by conspicuous secretion and licking with saliva. Again, upon a 

 sudden change to 20 G air temperatures, the maximally involved 

 heat loss mechanisms showed some delay in adjusting to the new 

 conditions, and body temperatures fell rapidly 2 C to 2 1/2 C. 

 The licking and salivation seemed, however, to stop immediately 

 upon cessation of the heat stress. At moderately low air tempera- 

 tures (3 C) two animals averaged slightly lower body temperatures 

 than normal for quiet animals at room temperature, whereas, one 

 animal over-compensated and showed a body temperature above 

 resting levels for most of the time. All animals shivered violently 

 during the cold exposure. Again I think it is highly important that 

 the body temperatures of the animals rose rapidly after removal 

 from the cold (Fig. 5), indicating again some persistence of the 

 compensatory mechanisms, this time violent shivering after the 

 actual cessation of the cold stress. Bartholomew tried to evaluate 

 the peripheral vascular situation by temperature measurements. 

 His data, as in Figure 6, shows very conspicuous gradients, in 

 particular along the tail. Bartholomew interprets the gradients 

 in proportion to the degree of local vasoconstriction. It seems, 

 however, conceivable that a counter- current effect, which in other 

 animals is responsible for tremendous temperature gradients in 

 peripheral extremities, might be in operation and thus conserve 

 heat. Again, Bartholomew noted that there is a gradual diminution 

 in peripheral vasoconstriction following exposure to cold. In my 

 own interpretations of his data these repeated findings of delays 

 in the transitions between regulatory states indicate some slow- 

 ness in the integrative apparatus controlling the effector responses 

 in temperature regulation. I will try to elaborate this assumption 

 in more detail when discussing my own data on the armadillo. 

 Bartholomew also exposed some wallabies to -10 Gfor two hours. 

 Such temperatures are never encountered by this species in its 

 normal habitat. At this time, both the subjects studied over-compen- 

 sated to the cold stress, and showed a deep body temperature more 

 than 1 C above the normal resting level. The feet and tail showed 

 a marked vasoconstriction, and the peripheral temperature ap- 

 proached C. Of great interest, the foot, and to a lesser degree 

 the tail, showed waves of vasodilation very similar to cold vaso- 

 dilation. Bartholomew's data indicate clearly that the ability to 



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