GENESIS, HEREDITY, AND VARIATION. 287 



That compounding and re-compounding through which we 

 pass from the simplest inorganic substances to the most com- 

 plex organic substances, has several concomitants. Each 

 successive stage of composition, presents us with atoms that are 

 severally larger or more integrated, that are severally more 

 heterogeneous, that are severally more unstable, and that are 

 more numerous in their kinds (First Principles, § 111). And 

 when we come to the substances of which living bodies are 

 formed, we find ourselves among multiplied, divergent groups 

 and sub-groups of compounds, the units of which are large, 

 heterogeneous, and unstable, in high degrees. There is no 

 reason to assume that this process ends with the formation of 

 those complex colloids which characterize organic matter. A 

 more probable assumption is, that out of the complex colloidal 

 atoms, there are evolved, by a still further integration, atoms 

 that are still more heterogeneous, and of kinds that are still 

 more multitudinous. What must be their properties ? Al- 

 ready the colloidal atoms are extremely unstable — capable 

 of being variously modified in their characters by very slight 

 incident forces ; and already the complexity of their polarities 

 prevents them from readily falling into those positions of 

 polar equilibrium which result in crystallization. Now the 

 organic atoms composed of these colloidal atoms, must be simi- 

 larly characterized in far higher degrees. Fur more numerous 

 must be the minute changes that can be wrought in them by 

 minute external forces ; far more free must they remain for a 

 long time to obey forces tending to re- distribute them ; and 

 far greater must be the number of their kinds. 



Setting out with these physiological units, the existence of 

 which various organic phenomena compel us to recognize, and 

 the production of which the general law of Evolution thus 

 leads us to anticipate ; we get an insight into the phenomena 

 of Genesis, Heredity, and Yariation. If each organism is built 

 of certain of these highly-plastic units peculiar to its species 

 — units which slowly work towards an equilibrium of their 

 complex polarities, in producing an aggregate of the specific 



