44 Till-: NERVOUS stSTKM AM) ITS (.'< >\Si:i;\ 'ATM >\ 



Psychologists have entertained and disciplined their pu- 

 pils by surest in; what would be the result of diverting 

 the impulses from one sense organ so that they should 

 enter the brain over a route normally belonging to a differ- 

 ent receptor system. The favorite proposition is to demand 

 that impulses originating in the eye be switched to the 

 auditory path, and that thoM- generated in the ear be 

 led into the brain along the fibers of the optic nerve. 

 The subject must then hear all that he used to see and 

 see all that he formerly heard. The lightning will he 

 for him a short, sharp sound, and the thunder a pro- 

 longed, flickering light. At a concert he will hear the 

 lights, the decorations, and the costumes, but he will 

 have the extraordinary privilege of seeing the progres- 

 sions of the music. \Ye cannot anticipate at all how it 

 will look. 



Unprofitable as such flights may appear, they at least 

 afford a clear recognition of the "Miillerian principle." 

 According to this the diverse effects produced by nerve- 

 impulses in various cases are due entirely to the direc- 

 tion which these impulses are made to take within the 

 nervous system, and not at all to their own variability. 

 Moreover, the effects of stimulation must be determined 

 far more by the choice of fibers to be acted upon than by 

 the kind of stimulation employed. The optic fibers are 

 usually made to bear impulses which have been initiated 

 in the retina under the influence of light, but it is possible 

 to start impulses along these same fibers by other means. 

 Thus, it is recalled from the old days of surgery without 

 anesthetic- that the cutting of the optic nerve a form 

 of mechanical stimulation was not productive of pain 

 beyond that already being endured, but of the sensation 

 of a flash of light. It is not certain that we can always 

 adhere strictly to the doctrine of the uniform character 

 of the nerve-impulses, but to do so as far as possible makes 

 for clearness. 



It is well just here to refer to a phenomenon often held 

 to be mysterious, though readily explained. This is the 



