JANSKY 



lactic acid and that this level of exertion can be sustained for long 

 periods. In practice, lactic acid is not usually measured, and maxi- 

 mal steady state metabolism during exercise is determined at the 

 highest running speed, which can be sustained for about 20-40 min- 

 utes. 



During exposure to cold there is also a marked increase in me- 

 tabolism which can be maintained for long periods. The question 

 therefore arises as to whether there is a relationship between the 

 maximal working metabolism and the highest level of metabolism 

 that can be obtained in the cold. 



Experiments on man have shown that it is possible to attain the 

 maximal steady state metabolic level only under intensive work con- 

 ditions and that the effect of coki does not add to the metabolic rate 

 during work (substitution theory- Lefevre, 1933, 1934). On the other 

 hand, tests on some small mammals have shown that maximal ox- 

 ygen consumption is possible with simultaneous application of work 

 and lowered temperatures, so that the working and cold thermogene- 

 sis occur at the same time, (addition theory- Chevillard, 1935; Hart, 

 1950; Hart and Heroux, 1955; Jansky, 1959, a, b, c). 



In the tests on small mammals, the measurement of maximal 

 steady state metabolism during work and exposure to cold is very 

 difficult, owing to the rapid development of hypothermia which event- 

 ually causes a decline in heat production. Figure 1 shows a distinct 

 drop in the oxygen consumption ofwhite mice which started immedi- 

 ately at the beginning of the work in extreme cold (Jansky, 1959a). 

 Decline of metabolism presumably due to hypothermia was found at 

 the lowest temperatures in most of the species investigated. 



Since the values obtained on hypothermic animals could not be 

 considered maximal, it was necessary, therefore, to perform the 

 tests atvarious temperatures to find the lowest temperature at which 

 working oxygen consumption was maximal and did notdecrease dur- 

 ing the test period (40 minutes) . 



Results obtained on various small mammals showed that there 

 were species differences in the effect of work and cold on metabol- 

 ism. In rabbits and lemmings (Hart and Heroux, 19 55) in white mice 



176 



