92 ORIGIN AND NATURE OF LIFE 



He deals, if possible, especially in studying 

 the elements with higher valencies, only with 

 compounds of simple type containing if 

 possible only one atom in the molecule 

 of the polyvalent element, and he directs his 

 attention to the compound which he can 

 prepare with the highest valency exhibited, 

 and in that compound univalent elements 

 so far as possible occupying the available 

 dynamic centres of the polyvalent element. 

 In his quest he is assisted by many experi- 

 mental touchstones which need not here be 

 considered in detail. 



Carbon is that one of all the elements that 

 concerns us most intimately because its high 

 valency and its unparalleled power of uniting 

 with itself as well as with other elements, 

 enables it to build up single molecules con- 

 taining very large numbers of atoms, and such 

 molecules form the basis for framing the 

 structure of living organisms. Without these 

 two properties of the carbon atom, life, at 

 least as it is known upon the earth, would be 

 impossible, and accordingly it may be well 

 to describe in outline, as simply as possible, 

 the proof that carbon is a tetrad element, 

 and the results in molecule building which 

 rest ultimately upon its remarkable power of 

 self-union. 



