DOMESTIC MAMMAL ADAPTATIONS 



3/4 

 B = 70 X W 



where B = basal metabolic rate per day in kcal 



W= body size in kg (Kleiber, 1947) 



Scholander (1955) writes as follows: 



The non- adaptability of the resting rate shows that the 

 heat production is notdetermined by the heat loss as one 

 might infer from the surface law of Rubner (1883) but 

 vice versa. Whatever the surface area happens to be, the 

 heat loss from it must be so regulated by various means 

 that it balances the heat production. In ahomeotherm one 

 might say that body temperature plays the first violin, 

 metabolic rate the second, and heat loss the third. 



The major, or practically only, adaptation which occurred was 

 the adjustment of the thermal insulation to bring the third violin 

 into harmony with the first and second. This adaptation was accom- 

 plished in various ways, and it led to differences in the temperature 

 distribution of various animals. 



Figure 2, also schematized from the data of Johnson et al. 

 (1958), shows the skin temperature as a function of the environ- 

 mental temperature. From 50 F to 90 F (10 C to 32 C) air 

 temperature the rabbit skin maintains an almost constant tem- 

 perature, whereas the temperature of the skin of cow and man 

 follows the environmental temperature. 



This temperature distribution is the result of the high insulating 

 power of the rabbit fur and the fact that man lacks this insulation. 

 The main resistance against heat loss and therefore the greatest 

 temperature gradient in naked man is located in the subcutaneous 

 layer. The cow has a less efficient fur than the rabbit. The difference 

 between rectal temperature and skin temperature, which is an index 

 for the resistance of the subcutaneous layers to heat flow, is shown 

 in Figure 3. 



As the environmental temperature rises, the skin temperature 

 of man and cow approaches the rectal temperature but does not reach 



245 



