CHEMISTRY 219 



In the more complex substances, such as 

 the various ring systems of organic chemistry, 

 it is not possible to discuss such problems of 

 molecular mechanics. There too, however, 

 hydrogen predominates over all other elements 

 except carbon, and that may well be taken as 

 a sufficient indication of its continued im- 

 portance. 



All of these considerations taken together 

 suffice, I believe, to prove, or at least to make 

 it exceedingly probable, that organic chemistry 

 is in truth a unique field, and that no other 

 elements can form compounds in such variety, 

 complexity, and number as carbon, hydrogen, 

 and oxygen. At any rate there can be no 

 possible doubt that the compounds of organic 

 chemistry are in these respects very remark- 

 able indeed, and that similar cases must be 

 extremely rare among all the possible systems 

 of compounds made up of all the known 

 elements. 



It follows from the peculiarities just ex- 

 plained that the first great factor in the com- 

 plexity of living organisms as we know them, 

 the complexity and variety of their chemical 

 constituents, depends principally upon the 

 nature of the elements which compose such 

 substances, and is most probably a unique, 

 certainly a very rare characteristic of matter. 



