THE CARBON BALANCE 553 



the same amount of work as he performed before becoming fatigued, 

 will do so at a much greater expenditure of energy. 



There is a diurnal variation in the respiratory exchange, which is in 

 general parallel with the body temperature ; it rises during the day, the 

 time of activity and work, and falls during the night, the time of rest 

 and sleep. Food also affects respiratory exchange, but it will be unnec- 

 essary to go into this further after what has been said on page 547. 



