SEGREGATION. 487 



recognition of it is the production in him of a like connected 

 group of sensations, by a like connected group of attributes. 

 That is to say, there is produced throughout the nerves con- 

 cerned, a combined set of changes, similar to a combined set 

 'of changes before produced. Considered analytically, each 

 such combined set of changes is a combined set of molecular 

 modifications wrought in the affected part of the organism. 

 On every repetition of the impression, a like combined set of 

 molecular modifications is superposed on the previous ones, 

 and makes them greater: thus generating an internal idea 

 corresponding to these similar external objects. Meanwhile, 

 another kind of plant produces in the brain of the botanist 

 another set of combined changes or molecular modifications 

 a set which does not agree with and deepen the one we 

 have been considering, but disagrees with it; and by repeti- 

 tion of such there is generated a different idea answering to 

 a different species. What now is the nature of this 



process expressed in general terms? On the one hand there 

 are the like and unlike things from which severally emanate 

 the groups of forces by which we perceive them. On the 

 other hand, there are the organs of sense and percipient 

 centres, through which, in the course of observation, these 

 groups of forces pass. In passing through these organs of 

 sense and percipient centres, the like groups of forces are se- 

 gregated, or separated from the unlike groups of forces ; and 

 each such series of groups of forces, parted in this way from 

 others, answering to an external genus or species, constitutes 

 a state of consciousness which we call our idea of the genus 

 or species. We before saw that as well as a separation of 

 mixed matters by the same force, there is a separation of 

 mixed forces by the same matter; and here we may further 

 see that the unlike forces so separated, work unlike struc- 

 tural changes in the aggregate that separates them struc- 

 tural changes each of which thus represents, and is equiva- 

 lent to, the integrated series of motions that has produced it. 

 By a parallel process, the connexions of co-existence and 



