24 THE DATA OP BIOLOGY. 



molecules are more heterogeneous than these elements ; tri- 

 atomic more heterogeneous than diatomic ; and the molecules 

 containing four elements more heterogeneous than those con- 

 taining three: the most heterogeneous of them being the 

 proteids, which contain two other elements. The hydrated 

 forms of all these compounds are more heterogeneous than 

 are the anhydrous forms. And most heterogeneous of all 

 are the molecules which, besides containing three, four, or 

 more elements, also exhibit the isomerism and polymerism 

 which imply unions in multiples. 



3. This formation of molecules more and more heteroge- 

 neous during terrestrial evolution, has been accompanied by 

 increasing heterogeneity in the aggregate of compounds of 

 each kind, as well as an increasing number of kinds; and 

 this increasing heterogeneity is exemplified in an extreme 

 degree in the compounds, non-nitrogenous and nitrogenous, 

 out of which organisms are built. So that the classes, 

 orders, genera, and species of chemical substances, gradually 

 increasing as the Earth has assumed its present form, in- 

 creased in a transcendent degree during that stage which 

 preceded the origin of life. 



9. Returning now from these partially-parenthetic ob- 

 servations, and summing up the contents of the preceding 

 pages, we have to remark that in the substances of which or- 

 ganisms are composed, the conditions necessary to that re-dis- 

 tribution of Matter and Motion which constitutes Evolution, 

 are fulfilled in a far higher degree than at first appears. 



The mutual affinities of the chief organic elements are not 

 active within the limits of those temperatures at which 

 organic actions take place; and one of these elements is 

 especially characterized by its chemical indifference. The 

 compounds formed by these elements in ascending grades of 

 complexity, become progressively less stable. And those 

 most complex compounds into which all these four elements 

 enter, together with small proportions of two other elements 



