234 THE PHENOMENA OF MOTION 



recognised as the mutual action of both ; and appears 

 as an alternating destruction and restoration of the state 

 of equilibrium. 



In regard to its absolute amount, the waste and supply 

 of matter is, in the different periods of life, unequal ; 

 but, in the state of health, the available vital force must 

 always be considered as a constant quantity, correspond- 

 ing to the sum of living particles. 



Growth, or the increase of mass, stands, at every 

 age, in a fixed relation to the amount of vital force con- 

 sumed as moving power. 



The vital force, which is expended for mechanical 

 purposes, is subtracted from the sum of the force avail- 

 able for the purpose of increase of mass. 



The active force, which is consumed in the body in 

 overcoming resistance (in causing increase of mass), 

 cannot, at the same time, be employed to produce me- 

 chanical effects. 



Hence it follows necessarily, that when, as in child- 

 hood, the supply exceeds the waste of matter, the me- 

 chanical effects produced must be less in the same 

 proportion. 



With the increase of mechanical effects produced, 

 the capacity of increase of mass or of the supply of 

 waste in living tissues must diminish in the same pro- 

 portion. 



A perfect balance between the consumption of vital 

 force for supply of matter and that for mechanical ef- 

 fects occurs, therefore, only in the adult state. It is 



