KLEIBEB 



The,surface area in square decimeters may be estimated to be 10 x 

 W , where Wis the body weight in kg. The heat capacity of the ani- 

 mal may be estimated as kg water xO.4 x kg dry matter in the ani- 

 mal (Kleiber, 1961). Assuming a water content of 68%, the heat 

 capacity of the animal would therefore amount to 0.81 kcal/ C per 

 kg body weight. The ratio of surf ace a re a to heat capacity then would 

 amount to 



2/3 . 



or 12.5 W (second column in Figure 18) 



0.81W ^ ^ ' 



' 2 

 The increase in body temperature from the storage of 2.5 kcal/dm 



then amounts to 2.5 x 12.5 W~ . This rise would be 31.4 C for 

 an animal weighting 1 kg and 1.4 C for a 10 ton super elephant. 

 A large animal, therefore, may comfortably survive discontinuous 

 daily heat loads which are fatal for smaller animals. When, how- 

 ever, the heat load is continued, the advantage of size is lost. 



Professor Regan at Davis noted that a cow can stand a good 

 deal of heat during the day when she cools off during the night, 

 whereas a constant rather moderately high temperature in an 

 air conditioned room may be fatal. 



The camel can take advantage of cool nights by letting its 

 body temperature decrease to 34 C (see Schmidt- Nielsen). A 

 human being could hardly stand this, nor could he let his body 

 temperature rise to 41 C when water is short and the day hot. 



Schmidt- Nielsen feels that this relatively large change in 

 body temperature should not be regarded as a failure regulation, 

 but rather as an adaptation which conserves water. It may be 

 more cautious to say that in this case the water economy at the 

 cost of an accurate temperature regulation proves advantageous 

 for survival. 



The difference between controlled and run away increase 

 in body temperature, the latter resulting from positive feedback, 

 is clearly shown in a plot of pigs' body temperature against time 

 of exposure to various environmental temperatures, observed by 

 Robinson and Lee (1942). 



272 



