BOOK V. 



OF MOTILITY. 

 CHAPTER I. 



OF THE BROWNIAN MOVEMENTS. 



The general properties of organised matter, with which we have 

 so far been occupied, are closely connected with the truly funda- 

 mental biological property, nutrition ; to speak correctly, they 

 are only its dependencies. It is otherwise with that which we 

 have now to examine. Doubtless, the faculty of movement is 

 subordinate to nutrition, which is the very essence of life, but it 

 differs from it ; it is, as it were, superadded to it. 



Before proceeding further, it is important to distinguish care- 

 fully between motility, an organic property, and movements, 

 essential attributes of every organic and inorganic matter. At 

 the present time, most men of science, and a certain number of 

 thinkers, have finally broken with the old metaphysical distinc- 

 tion, which, with one stroke, cut the universe into two parts, 

 having between them only relations of contingency. We have 

 ceased to abstract the active qualities of the material substance 

 from the substance itself ; we no longer figure the world to our- 

 selves as constituted by an extended substance, but in itself 

 perfectly inert, ceaselessly incited and put in motion by an im- 

 palpable agent called force. The ancient divorce no longer 



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