INTRODUCTION. 7 



factorily by the manner in which they increase. The 

 various parts or organs of which such bodies are composed 

 are not homogeneous in their structure, like those of sim- 

 ple minerals ; and their increase is effected by an assimi- 

 lation of certain particles adapted to its growth, which 

 are received into the system through certain cavities, or 

 vessels, from whence they are elaborated, by a peculiar 

 process, into specific compounds, adapted to the nutri- 

 tion and development of the individual. These effects 

 depend upon the presence and activity of a distinct 

 force, peculiar to the condition under which organised 

 matter exists, viz. that mysterious principle which we 

 call " life," a something totally different in its mode 

 of action from any of the forces to which unorganised 

 bodies are subjected ; and capable of controlling, and, to 

 a certain extent, of counteracting, the effects of those 

 forces. One striking peculiarity in the vital force is its 

 variable condition, and ultimate secession from all or- 

 ganised bodies whatever. However effectual, for a 

 time, in counteracting the influences of the two other 

 great forces of nature, attraction and affinity, a period, 

 sooner or later, does always arrive, in which it ceases 

 to operate, and abandons to silence and inactivity the 

 dust and ashes which it had for a little while collected, 

 and employed in forwarding the high interests of ani- 

 mated nature. 



(7-) Animals and Vegetables. We may distinguish 

 organised bodies into animals and vegetables ; and our 

 daily experience is sufficient to satisfy us of the pro- 

 priety of such a division. Yet is it extremely difficult, 

 and has hitherto baffled the attempts of naturalists, 

 to point out the precise limits which separate these two 

 kingdoms of organised nature ; and no definitions of 

 what is a plant, and what is an animal, have yet been 

 framed sufficiently guarded and precise to satisfy all the 

 conditions under which different organised bodies are 

 found ; but, to this day, there are some objects which 

 it is very doubtful under which class they ought to be 

 arranged. Among the higher tribes of organised bodies, 

 B 4 



