216 THE PHENOMENA OF MOTION 



has been expended in producing mechanical effects. 

 For the waste of matter, in consequence of motion and 

 laborious exertion, is extremely various in different 

 individuals. 



If we reflect, that the slightest motion of a finger 

 consumes force ; that in consequence of the force ex- 

 pended, a corresponding portion of muscle diminishes 

 in volume ; it is obvious, that an equilibrium between 

 supply and waste of matter (in living tissues) can only 

 occur when the portion separated or expelled in a life- 

 less form is, at the same instant in which it loses its 

 vital condition, restored in another part. 



The capacity of growth or increase in mass depends 

 on the momentum of force belonging to each part ; 

 and must be capable of continued manifestation (if 

 there be a sufficient supply of nourishment), as long 

 as it does not lose this momentum, by expending it, 

 for example, in producing motion. 



In all circumstances, the growth itself is restricted 

 to the time ; that is to say, it cannot be unlimited in 

 a limited time. 



A living part cannot increase in volume at the same 

 moment in which a portion of it loses the vital con- 

 dition, and is expelled from the organ in the form of 

 a lifeless compound ; on the contrary, its volume must 

 diminish. 



The continued application of the momentum of force 

 in living tissues to mechanical effects determines, there- 

 fore, a continued separation of matter ; and only from 



