Respiration 



the digested food is transformed. We say 

 of someone who puts extreme energy into 

 his work that he is burning the candle at 

 both ends. This is another popular saying 

 which agrees perfectly with our most certain 

 knowledge of the facts of life. There is not 

 the least motion, not a limb stirs, without 

 causing an expenditure of fuel in proportion 

 to the force exerted, and this fuel is provided 

 by the blood, which is itself maintained by 

 food. To walk, to run, to become excited, 

 to work, to take trouble, is literally to burn 

 the blood. This is the reason why activity 

 and hard work excite the need of eating, 

 and why it is reduced by repose and idleness. 



45 



