THE PAST CONDITION OF ORGANIC NATURE. 29 



plant obtained the materials constituting its substance 

 by a peculiar combination of matters belonging entirely 

 to the inorganic world ; that, then, the animal was con- 

 stantly appropriating the nitrogenous matters of the 

 plant to its own nourishment, and returning them back 

 to the inorganic world, in what we spoke of as its 

 waste; and that, finally, when the animal ceased to 

 exist, the constituents of its bodv were dissolved and 

 transmitted to that inorganic world whence they had 

 been at first abstracted. Thus we saw in both the 

 blade of grass and the horse but the same elements 

 differently combined and arranged. We discovered a 

 continual circulation going on, — the plant drawing in 

 the elements of inorganic nature and combining them 

 into food for the animal creation; the animal bor- 

 rowing from the plant the matter for its own support, 

 giving off during its life products which returned im- 

 mediately to the inorganic world; and that, eventually, 

 the constituent materials of the whole structure of both 

 animals and plants were thus returned to their original 

 source : there was a constant passage from one state of 

 existence to another, and a returning back again. 



Lastly, when we endeavoured to form some notion of 

 the nature of the forces exercised by living beings, Ave 

 discovered that they — if not capable of being subjected 

 to the same minute analysis as the constituents of those 

 beings themselves— that they were correlative with — 

 that they were the equivalents of the forces of inorganic 

 nature — that they were, in the sense in which the term 

 is now used, convertible with them. That was our 

 general result. 



And now, leaving the Present, I must endeavour 



