336 TJ. S. NATIONAL MUSEUM BULLETIN 217 



Essentials for Maintaining Body Temperature 



Before his sacrifice to the political tempers of the French revolu- 

 tion, Lavoisier (1Y77) had demonstrated that the production of animal 

 heat could be ascribed to the oxidation of carbon and hydrogen in the 

 animal's body. Since that time physiological complications have often 

 been allowed to obscure the view that the heat produced by animal 

 combustions must pass to their environment in accordance with phys- 

 ical laws for the exchange of heat. The difficulty has been largely 

 methodological, and has arisen because man and the domestic and 

 laboratory animals commonly used for metabolic studies are so little 

 accustomed to cold that the factors of heat exchange are not large 

 enough for their relations to be readily apparent. The contrast be- 

 tween the conditions for heat exchange in arctic and tropical animals 

 presented their heat exchange in dimensions of such contrast that the 

 essential physical factors of the process could be related in a simple 

 form of Newton's law of cooling (Scholander, Hock, Walters, John- 

 son, and Irving 1950). 



Heat escapes from a warm body to cooler surroundings by conduc- 

 tion at a rate which is proportional to the difference in temperature 

 between the body and its surroundings. Warm-blooded animals, in or- 

 der to maintain a constant temperature, must produce as much heat 

 as escapes from their bodies. The loss of heat from animals proceeds 

 through surfaces which are insulated. Fur and feathers afford the 

 conspicuous insulation of animals but other natural insulating sys- 

 tems also serve in the conservation of bodily heat. If all the devices 

 resisting the loss of heat are regarded as components which combine 

 to provide insulation in still air, the system preserving body tempera- 

 ture can be described by the use of Newton's law of cooling (Scho- 

 lander, Hock, Walters, Johnson, and Irving, 1950), 



where Tb and T^. are the temperatures of the animal body and of the 

 surrounding air, / is the overall insulation of the animal, H is the 

 production of heat by metabolism, and K is the factor appropriate to 

 relate the units of measurement used. 



In order to compare heat exchange among animals of various sizes 

 the basal metabolic rate of each animal was represented as 100 and 

 the observed metabolic rates were plotted against air temperatures. 

 Figure 18, which shows these relations among arctic and tropical 

 species of mammals and birds, indicates that the larger arctic birds and 

 mammals maintained their basal metabolic rates in cold and could ap- 

 parently sustain any arctic winter weather without heat beyond that 

 produced at the level of basal metabolism. Tropical animals, on the 



