266 THE FITNESS OF THE ENVIRONMENT 



the oxide of silicon, is the most inert and 

 immobile of rocks ; the oxide of boron is only 

 less available as a movable constituent of the 

 environment; and there is no other stable 

 compound of either element which can be 

 compared with carbonic acid for its mobility. 

 It must be remembered that this property 

 is the result of two independent characteris- 

 tics of the latter substance, its gaseous na- 

 ture, and the precise degree of its solubility 

 in water. Finally, the regulation of the 

 reaction of aqueous solutions by means of 

 carbonic acid has to be taken into account. 



Hence it may be concluded that hydrogen, 

 oxygen, and carbon, water and carbonic 

 acid, are not to be rivaled in their own qual- 

 ities, even as these cannot be balanced by 

 others which they do not possess. 



On the whole, then, we may believe that the 

 physico-chemical characteristics of material 

 systems and material processes have been com- 

 prehensively examined in the course of the 

 present study. Accordingly, we may finally 

 conclude that the fitness of water, carbonic 

 acid, and the three elements make up a unique 

 ensemble of fitness for the organic mechanism. 

 The search, however incomplete, has certainly 

 not overlooked properties so important and 

 so numerous, or compounds and elements so 



