374 PHYSIOLOGICAL DEVELOPMENT. 



mutually cancelled : if not locally, then at some centre to 

 which each unbalanced motion travels until it meets with 

 some opposite unbal incjd motion to destroy it. Still, involved 

 as these actions must become, it is possible to see how the 

 general principle illustrated by the simple case above sup- 

 posed, will continue to hold. For al\va3's the molecular 

 motion proceeding from aii}^ one differentiated part, will travel 

 most readily towards that place where a molecular motion 

 most complementary to it in kind exists — no matter whether 

 this complementary molecular motion be that proceeding 

 from any one other organ, or the resultant of the molecular 

 motions proceeding from many other organs. So that the 

 tendency will be for each channel of communication or nerve, 

 to unite itself with some centre or ganglion, where it comes 

 into relation with other nerves. And if there be any parts 

 of its peculiar molecular motion uncancelled by the mole- 

 cular motions it meets at this centre ; or if, as will pro- 

 bably happen, the average molecular motion which it there 

 unites to produce, differs from the average molecular motion 

 elsewhere ; then, as before, there will arise a discharge along 

 another channel or nerve to another centre or ganglion, where 

 the residuary difference may be cancelled by the differences 

 it meets ; or from whence it may be still further propagated 

 till it is so cancelled. Thus there will be a tendency to a 

 general nervous integration keeping pace with the differen- 

 tiation. 



Of course this must be taken as nothing more than the 

 indication of initial tendencies — not as an hypothesis suffi- 

 cient to account for all the facts. It leaves out of sight the 

 origin and functions of ganglia, considered as something 

 more than nerve-junctions. Were there only these lines of 

 easy transmission of molecular disturbance, a change set up 

 in one organ could never do more than produce its equivalent 

 of change in some other or others ; and there could be none 

 of that large amount of motion initiated by a small sensation, 

 vhich we habitually see. The facts show, unmistakably, that 



