IN THE ANIMAL ORGANISM. 221 



that a rapid transformation of muscular fibre, or, as 

 it may be called, a rapid change of matter, deter- 

 mines a greater 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 con- 

 sumed 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 external 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 in- 

 capable of resisting the action of the oxygen con- 

 veyed to it by the arterial blood, and should be 

 deprived of the power to overcome chemical re- 

 sistance, unless the momentum of the vital force, 

 which had given to it all these properties, had been 

 expended for other purposes? 



