942 THE VITAL ENERGY EXPENDED BY 



quiescence of the brain, nerves, and voluntary 

 muscles, that respiration and sanguification, se- 

 cretion and nutrition, are greatly augmented 

 during violent exercise : for it is well known 

 that the more vigorously any organ is exercised, 

 the more abundantly is it supplied with arterial 

 blood. Hence it is, that more food is required by 

 men who take much exercise, than by such as lead 

 a sedentary life. Yet as the animal heat by 

 which the organic particles of blood are united 

 with the solids, is more rapidly expended by 

 exertion through the day, than it is obtained by 

 respiration, the vital affinity by which the said 

 particles are held in combination with the solids 

 is very soon dissolved, when they are removed by 

 the absorbents, and replaced by new ones, as 

 shown in the foregoing parts of this work. 



It is only, however, the brain, nerves, and vo- 

 luntary organs, whose substance and power are 

 so greatly exhausted by exercise ; for as the action 

 of the lungs, heart, stomach, bowels, and other 

 involuntary organs, is more nearly the same at 

 all times, the process of renovation is generally 

 equal to that of waste, and they never require 

 absolute repose, but continue in action through- 

 out the whole period of existence. 



The most remarkable difference betiveen exercise 

 and sleep is, that during the former, the expenditure 

 exceeds the income ; whereas, during the latter, the 

 income exceeds the expenditure. For example, if 

 the annual income of an individual be 500 pounds, 



