488 SEGREGATION. 



sequence among impressions, become sorted into kinds and 

 grouped simultaneously with the impressions themselves. 

 When two phenomena that have been experienced in a 

 given order, are repeated in the same order, those nerves 

 which before were affected by the transition are again af- 

 fected; and such molecular modification as they received 

 from the first motion propagated through them, is increased 

 by this second motion along the same route. Each such mo- 

 tion works a structural alteration, which, in conformity with 

 the general law set forth in Chapter IX., involves a diminu- 

 tion of the resistance to all such motions that afterwards 

 occur. The segregation of these successive motions (or more 

 strictly, the permanently effective portions of them expend- 

 ed in overcoming resistance) thus becomes the cause of, and 

 the measure of, the mental connexion between the impres- 

 sions which the phenomena produce. Meanwhile, phenom- 

 ena that are recognized as different from these, being phe- 

 nomena that therefore affect different nervous elements, will 

 have their connexions severally represented by motions 

 along other routes; and along each of these other routes, the 

 nervous discharges will severally take place with a readiness 

 proportionate to the frequency with which experience repeats 

 the connexion of phenomena. The classification of relations 

 must hence go on pari passu with the classification of the re- 

 lated things. In common with the mixed sensations received 

 from the external world, the mixed relations it presents, 

 cannot be impressed on the organism without more or less 

 segregation of them resulting. And through this continu- 

 ous sorting and grouping together of changes or motions, 

 which constitutes nervous function, there is gradually 

 wrought that sorting and grouping together of matter, 

 which constitutes nervous structure. 



§ 128. In social evolution, the collecting together of the 

 like and the separation of the unlike, by incident forces, is 

 primarily displayed in the same manner as we saw it to be 



