12 INTRODUCTION. 



subject to their ordinary chemical affinities , they 

 are no longer restrained from separating', and the 

 dissolution of the late living body follows, with 

 greater or less rapidity. It was by means of 

 the vital motion that this dissolution was prevented 

 before, and the material corporeal elements pre- 

 served for a time in a state of union. All living- 

 bodies die after a time, the extreme limit of which 

 is fixed in every species. Death is a necessary 

 effect of life, which, by its very action, seems gra- 

 dually to alter the structure of the body, so as to 

 render its continuation impossible ; for a living body 

 undergoes a gradual but constant change during 

 the whole period of its existence ; at first it increases 

 in dimensions, according to certain proportions and 

 limits fixed and determined for every species, and 

 afterwards it augments in density in most of its in- 

 dividual parts. It is this latter change which ap- 

 pears to be the cause of natural death. 



If we further enlarge our observations to the 

 various sorts of living bodies, we shall find a princi- 

 ple of structure and being common to them all, 

 which a little reflection will convince us to be essen- 

 tially requisite to that faculty, analogous to a vor- 

 tex, with which the vital action has been assimilated. 

 We should observe, that solid parts are necessary 

 to preserve the various forms of living bodies, as 

 well as fluids, to sustain in them the necessary 

 motion *•. 



* It may be observed that the opinions of Cuvier, respecting life 

 and organization, entertained both at this place and in other parts 



