360 PHYSIOLOGICAL DEVELOPMENT. 



Now among the extremely unstable organic colloids, such a 

 phenomenon is far more likely to happen. Suppose, then, that 

 the nerve-colloid is one of which the molecules are changed in 

 form by a passing wave of extra agitation, but resume their 

 previous form when the wave has passed: the previous form 

 being the most stable under the conditions which then recur. 

 What follows ? It follows that these molecules will be ready 

 again to undergo isomeric transformation when there again 

 occurs the stimulus ; will, as before, propagate the transforma- 

 tion most along the tract where such molecules are most 

 abundant ; will, as before, tend to form new molecules of their 

 own type; will, as before, make the line along which they lie 

 one of easier transfer for the molecular agitation. Every 

 repetition will help to increase, to integrate, to define more 

 completely, the course of the escaping molecular motion — 

 extending its remoter part while it makes its nearer part 

 more permeable — will help, that is, to form a line of dis- 

 charge, a line for conducting impressions, a nerve. 



Such seems to me a not unfair series of deductions from 

 the known habitudes of colloids in general and the organic 

 colloids in particular. And I think that the implied nature 

 and properties of nerve correspond better with the observed, 

 phenomena than do the nature and properties implied by 

 other hypotheses. Of course the speculation as it here stands 

 is but tentative, and leaves much unexplained. It gives no 

 obvious reply to the questions — what causes the formation of 

 nerves in directions adapted to the needs? what determines 

 their appropriate connexions ? — questions, however, to which, 

 when we come to deal with physiological integration, we may 

 find not unsatisfactory answers. Moreover it says nothing 

 about the genesis of ganglia. A ganglion, it is clear, must 

 consist of a colloidal matter equally unstable, or still more 

 unstable, which, when disturbed, falls into some different 

 molecular arrangement, perhaps chemically simpler, and gives 

 out in so doing a large amount of molecular motion — serves 

 as a reservoir of molecular motion which may be suddenly 



