THE BEGINNINGS OF LIFE. 163 



tion. We cannot do better than quote what Mr. Her- 

 bert Spencer writes on this subject in his c Principles of 

 Biology/ c We set out with molecules 1 / he says, c one 

 degree higher in complexity than those molecules of 

 nitrogenous colloidal substance into which organic 

 matter is resolvable; and we regard these somewhat 

 more complex molecules as having the implied greater 

 instability, greater sensitiveness to surrounding in- 

 fluences, and consequent greater mobility of form. 

 Such being the primitive physiological units, organic 

 evolution must begin with the formation of a minute 

 aggregation of them an aggregate showing vitality only 

 by a higher degree of that readiness to change its form of 

 aggregation which colloidal matter in general displays $ and 

 by its ability to unite the nitrogenous molecules it meets 

 with, into complex molecules like those of which it is 

 composed. Obviously the earliest forms must have 

 been minute ; since in the absence of any but diffused 

 organic matter, no form but a minute one could find 

 nutriment. Obviously, too, it must have been struc- 

 tureless; since as differentiations are producible only 

 by the unlike actions of incident forces, there could 

 have been no differentiations before such forces had 

 had time to work. Hence distinctions of parts like 

 those required to constitute a cell were necessarily 



1 Mr. Spencer here refers to chemical molecules of a very complex 

 nature, and not to minute visible granules. For an account of these 

 complex molecules or 'physiological units' see ' Prin. of Biol.' vol. i. 

 p. 182. 



M 2, 



