82 HOMOIOTHERMISM 



into carbohydrates. The fact that a hibernating marmot 

 increases in weight during hibernation indicates that 

 oxygen is actually retained. A marmot's respiratory 

 quotient under such conditions is about 0.30. 



In a study of hibernation in the ground squirrel, Citel- 

 his tridecemlineatus (Mitchell), Johnson (1928) showed 

 that during the period of torpidity the body temperature 

 fell as low as to 2 deg. C, which was within one degree 

 of the surrounding temperature. During the period of 

 hibernation a ground-squirrel sometimes loses 40 per 

 cent of its body weight. Johnson also observed that the 

 respirations dropped from 100-200 per minute in active 

 animals to 1-4 in torpid animals. The rate of heart 

 beat likewise ranged from 200 to 350 per minute in the 

 active animals but decreased to a minimum of 5 beats 

 per minute in hibernating individuals. These observa- 

 tions indicate a very low metabolism during hibernation 

 and a close approximation to the poikilothermal condi- 

 tion during the cold seasons. 



Hibernation is a condition apparently fairly well dis- 

 tributed through a variety of mammals. Martin (1903) 

 observed Echidna in hibernation, during which it took 

 neither food nor water and showed a body temperature 

 which followed that of its surroundings within 0.5 deg. C. 

 Animals remained in a torpid state for as much as 4 

 months. The production of heat in Echidna was propor- 

 tional to the difference in temperature between animal 

 and environment. 



Mammals are descended from poikilothermal animals. 

 Some have reached a less perfectly homoiothermic state 

 than others and perhaps have some imperfections in their 

 heat regulating mechanism. These have made a virtue 

 of necessity by becoming hibernators. They cannot sus- 

 tain the temperature at the level required for a continu- 



