ORGANIC MATTER. 23 



essay on " The Nebular Hypothesis " (see Essays, vol. I, 

 p. 155). On tracing out the process of compounding and re- 

 compounding by which, hypothetically, the elements them- 

 selves and afterwards their compounds and re-compounds 

 have arisen, certain cardinal facts become manifest. 



1. Considered as masses, the units of the elements are the 

 smallest, though larger than the units of the primordial 

 matter. Later than these, since they are composed of them, 

 and since they cannot exist at temperatures so high as those 

 at which the elements can exist, come the diatomic com- 

 pounds oxides, chlorides, and the rest necessarily larger in 

 their molecules. Above these in massiveness come the 

 molecules of the multitudinous salts and kindred bodies. 

 When associated, as these commonly are, with molecules of 

 water, there again results in each case increase of mass ; and 

 unable as they are to bear such high temperatures, these 

 molecules are necessarily later in origin than those of the 

 anhydrous diatomic compounds. Within the general class 

 of triatomic compounds, more composite still, come the 

 carbo-hydrates, which, being able to unite in multiples, form 

 still larger molecules than other triatomic compounds. De- 

 composing as they do at relatively low temperatures, these 

 are still more recent in the course of chemical evolution ; and 

 with the genesis of them the way is prepared for the genesis 

 of organic matter strictly so called. This includes the 

 various forms of protein-substance, containing four chief 

 elements with two minor ones, and having relatively vast 

 molecules. Unstable as these are in presence of heat and 

 surrounding affinities, they became possible only at a late 

 stage in the genesis of the Earth. Here, then, in that chemi- 

 cal evolution which preceded the evolution of life, we see 

 displayed that process of integration which is the primary 

 trait of evolution at large. 



2. Along with increasing integration has gone progress in 

 heterogeneity. The elements, regarding them as compound, 

 are severally more heterogeneous than " protyle." Diatomic 



