DOMESTIC MAMMAL ADAPTATIONS 

 REGULATION AGAINST COOLING 



By cooling I mean a decrease in temperature and, to the best 

 of my knowledge, that is what Newton meant by cooling when he 

 formulated his law of cooling which is erroneously applied when one 

 means loss of heat rather than of temperature. Temperature reg- 

 ulation means prevention of cooling but not prevention of heat loss. 



The classic example for adaptation to cold has been given by 

 Hoesslin (1888). He set out to test experimentally Rubner's theory 

 that the metabolic rate of homeo therms is proportional to their sur- 

 face area because their heat loss is proportional to their surface 

 area. Hoesslin argued if the metabolic rate is governed by the heat 

 requirement, then it should be directly proportional to the difference 

 between environmental temperature and body temperature. To test 



this deduction, Hoesslin raised one dog at 32 C and a twin brother 



o 

 of that dog in the refrigerator at 5 C. From his records of food 



consumption and his estimate of body substance produced, Hoesslin 



concluded that the dog raised at 5 C had a metabolic rate only 12% 



above that of his brother raised at 32 C, The difference between 



body temperature and environmental temperature of the cold dog was 



about six times as great as the corresponding difference for the hot 



dog. 



Hoesslin concluded that heat requirement could not be the deter- 

 mining factor in the control of metabolic rate or the explanation for 

 the surface law. He observed that the cold dog's pelt weighed 3.6 

 times as much as that of the hot dog, indicating an adaptation of in- 

 sulation to environment. It may be that the adaptation was mainly on 

 the side of the hot dog, that his fur was abnormally light. We now 

 would accept Hoesslin's argument that the metabolic rate of his hot 

 dog was not determined by heat requirement, but we would maintain 

 that the metabolic rate of the cold dog presumably reflected a ther- 

 mostatic heat requirement. This assumption is justified by the rela- 

 tion of metabolic rates to body temperatures of various animals 



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