210 THE PHENOMENA OF MOTION 



amount of mechanical force ; and conversely, that a 

 greater amount of mechanical motion (of mechanical 

 force expended in motion) determines a more rapid 

 change of matter. 



From this decided relation between the change of 

 matter in the animal body and the force consumed in 

 mechanical motion, no other conclusion can be drawn 

 but this, that the active or available vital force in certain 

 living parts is the cause of the mechanical phenomena in 

 the animal organism. 



The moving force certainly proceeds from living 

 parts ; these parts possessed a momentum of force or 

 of motion, which they lost in proportion as other parts 

 acquired a momentum of force or of motion ; they lose 

 their capacity of growth, and their power to resist ex- 

 ternal causes of change. It is obvious that the ultimate 

 cause, the vital force, from which they acquired those 

 properties, has served for the production of mechanical 

 force, that is, has been expended in the shape of 

 motion. 



How, indeed, could we conceive, that a living part 

 should lose the condition of life, should become inca- 

 pable of resisting the action of the oxygen conveyed to 

 it by the arterial blood, and should be deprived of the 

 power to overcome chemical resistance, unless the mo- 

 mentum of the vital force, which had given to it all 

 these properties, had been expended for other pur- 

 poses ? 



By the power of the conductors, the nerves, to 



