434 THE RESPIRATION 



miles caused an average rise of 0.8 F. on a cool day, and of 1.4 F. on 

 a hot day. The temperature returns to normal very quickly after the 

 exercise, and while it is raised there is by no means the upset in the 

 bodily functions that is observed in fever. For one thing, the metab- 

 olism in the two cases is quite different; in fever, protein catabolism is 

 abnormally great, whereas in muscular exercise this is not the case, 

 oxidation of carbohydrates and fat being the source of the energy. It 

 is very likely that rise in blood temperature is in part responsible for 

 the acceleration of the heart that occurs during exercise, and for in- 

 creased excitability of the medullary nerve centers. It probably also as- 

 sists in hurrying the oxidative changes in the active muscles, and, by 

 lessening the affinity of hemoglobin for oxygen, facilitates the liberation 

 of this gas to the plasma. 



