ORGANIC MATTER. 5 



One more fact, that is here of great interest for us, must 

 be set down. These four elements of which organisms are 

 almost wholly composed, present us with certain extreme 

 antitheses. While between two of them we have an unsur- 

 passed contrast in chemical activity ; between one of them 

 and the other three, we have an unsurpassed contrast in 

 molecular mobility. While carbon, by successfully resisting 

 fusion and volatilization at the highest temperatures that can 

 be produced, shows us a degree of atomic cohesion greater 

 than that of any other known element, hydrogen, oxygen, and 

 nitrogen, show the least atomic cohesion of all elements. And 

 while oxygen displays, alike in the range and intensity of its 

 affinities, a chemical energy exceeding that of any other sub- 

 stance (unless fluorine be considered an exception), nitrogen 

 displays the greatest chemical inactivity. Now on calling to 

 mind one of the general truths arrived at when analyzing 

 the process of Evolution the probable significance of this 

 double difference will be seen. It was shown (First Principles, 

 123) that, other things equal, unlike units are more easily 

 separated by incident forces than like units are that an inci- 

 dent force falling on units that are but little dissimilar does 

 not readily segregate them ; but that it readily segregates 

 them if they are widely dissimilar. Thus, these two extreme 

 contrasts, the one between physical mobilities, and the other 

 between chemical activities, fulfil, in the highest degree, a 

 a certain further condition to facility of differentiation and 

 integration. 



2. Among the binary combinations of these four chief 

 organic elements, we find a molecular mobility much less 

 than that of these elements themselves ; at the same time 

 that it is much greater than that of binary compounds in 

 general. Of the two products formed by the union 



of oxygen with carbon, the first, called carbonic oxide, which 

 contains one atom of carbon to one of oxygen (expressed by 

 the symbol C O), is an incondensible gap ; and the second 



