236 THE PHENOMENA OF MOTION 



roller gained in force ; by this process force was ob- 

 viously collected, accumulated in the velocity ; but in 

 this sense force does not accumulate in the living or- 

 ganism. 



The restoration of force is effected, in the animal 

 body, by the transformation of the separated parts, des- 

 tined for the production of force, and by the expendi- 

 ture of the active vital force in causing formation of 

 new parts ; and, with the restoration of the separated or 

 effete parts, the organism recovers a force equal to that 

 which has been expended. 



It is plain, that the vital force manifested, during 

 sleep, in the formation of new parts 'must be equal to 

 the whole sum of the moving power expended in the 

 waking state in all mechanical effects whatever, plus a 

 certain amount of force, which is required for carrying 

 on those involuntary motions which continue during 

 sleep. 



From day to day, the laboring man, with sufficient 

 food, recovers, in seven hours' sleep, the whole sum 

 of force ; and without reckoning the force necessary 

 for the involuntary motions which may be considered 

 equal in all men, we may assume, that the mechanical 

 force available for work is directly proportional to the 

 number of hours of sleep. 



The adult man sleeps 7 hours, and wakes 17 hours ; 

 consequently, if the equilibrium be restored in 24 hours, 

 the mechanical effects produced in 17 hours must be 



