CHAEACTERICnCS OF VITAL ACTIVITY. 407 



If, in the first place, we inquire what it is that essentially 

 distinguishes Vital from every kind of Physical activity, we 

 find this distinction most characteristically expressed in the 

 fact that a germ endowed with Life, developes itself into an 

 organism of a type resembling that of its parent ; that this 

 organism is the subject of incessant changes, which all tend 

 in the first place to the evolution of its typical form, and sub- 

 sequently to its maintenance in that form, notwithstanding the 

 antagonism of Chemical and Physical agencies, which are 

 continually tending to produce its disintegration ; but that, as 

 its term of existence is prolonged, its conservative power de- 

 clines so as to become less and less able to resist these disinte- 

 grating forces, to which it finally succumbs, leaving the organ- 

 ism to be resolved by their agency into the components from 

 which its materials were originally drawn. The history of a 

 living organism, then, is one of incessant change; and the 

 conditions of this change are to be found partly in the organ- 

 ism itself, and partly in the external agencies to which it is 

 subjected. That condition which is inherent in the organism, 

 being derived hereditarily from its progenitors, may be con- 

 veniently termed its germinal capacity ; its parallel in the in- 

 organic world being that fundamental difference in properties 

 which constitutes the distinction between one substance, 

 whether elementary or compound, and another ; in virtue of 

 which each " behaves" in its own characteristic manner when 

 subjected to new conditions. 



Thus, although there may be nothing in the aspect or sen- 

 sible properties of the germ of a Polype, to distinguish from 

 that of a Man, we find that each develops itself, if the requi- 

 site conditions be supplied, into its typical form, and no other; 

 if the developmental conditions required by either be not sup- 

 plied we do not find a different type evolved, but no evolution 

 at all takes place.* 



* It is quite true that among certain of the lower tribes, both of PJants 



