LETTER IX. 



81 



quently transformed into the various organised struc- 

 tures — and these again knit together and built up into 

 the several plants and animals which we see around 

 us, — and which affinities are the most general and fun- 

 damental of all vital actions, — are exceedingly transient 

 in their agency. Their office may be said to cease in 

 each structure on the completion of the structure ; and 

 if this structure have no special purpose to serve in 

 Nature other than that connected with its formation 

 as an organised tissue, — if the object of its existence 

 end with its formation, its vitality may be said to cease 

 with the play of the chemical and plastic affinities by 

 which it was formed ; and losing its vitality, it tends . 

 (as is the tendency of all dead organic matter) to 

 revert back to the condition of inorganic. Add to this, 

 that the more active and energetic the agency of these 

 affinities, i, e, the more rapid the formation of the 

 structure, the shorter is the duration of its vitality. 



6. If, on the other hand, the structure have some 

 specific end to serve; and if, in order thereto, its 

 maintenance for a time in a living state be required, 

 this can be accomplished only by a continual change 

 and reneival of substance. For the general law of tran- 

 sient vitality still attaches to its several molecules ; and 

 these, as they die, must be removed and replaced by 

 new — a process involving the continued agency of the 

 affinities by which the structure was at the first formed, 

 exerted on foreign matters taken in from without — 



F 



