KLEIBEP 



obviously reflecting the insulating power of their body covering as 

 shown in Figure 9. 



We simplify the situation by the scheme in Figure 10 . If the 

 dogs behaved strictly like ordinary thermostats, then the metabolic 

 rate of the hot dog would be on the line between the rate of the hot 

 dog and the rate zero reached when the environmental temperature 

 becomes equal to the body temperature. On the scale of our figure 

 the hot dog would produce about 16% of the "normal" rate marked 

 100. The hot dog, however, produces almost as much heat as his 

 cold brother and operates special devices to get rid of the excess 

 heat. Obviously, the metabolic rate of the hot dog cannot be explained 

 as a heat requirement. Rubner realized that, and he explained the 

 surface law of animal metabolism as heat requirement proportional 

 to surface area in a cold environment and as necessary cooling 

 power also proportional to surface area in a hot environment. 



There is, however, a difference between the two dogs in their 

 immediate reaction to cold. If the hot dog were suddenly brought to 

 the cold living quarters of his brother, he would presumably shiver 

 and produce more heat than the cold-adapted litter mate. If he stayed 

 long enough in the wintery climate and if he had enough youthful 

 adaptability he would gradually grow a fur as thick as that of his 

 brother and quit shivering; then presumably the two dogs would have 

 the same metabolic rates. The rise in metabolic rate is known as 

 "chemical," or metabolic temperature regulation. By that term, 

 Rubner simply meant an increase in the rate of chemical processes, 

 whether or not connected with muscular movement such as shivering. 

 The idea of chemical temperature regulation as contrasted to reg- 

 ulation involving shivering is a later and not too useful complication. 

 The change in the insulation, in contrast to the change in metabolic 

 rate, is known as "physical" temperature regulation, and, if it in- 

 volves slow processes such aschangingone'sfur,it is classified as 

 "acclimatization." 



Scholander reports that dogs truly acclimatized to the arctic 

 regions have a critical temperature as low as -40 C. This shows 

 that domestication has not led to a degeneration of the dog or at 

 least has left the dog the possibility of overcoming the softening 



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