54 Dr. W. Pole on Colour-Blindness. 



But it is not hereby excluded that this wanting colour might 

 also be wanting to the normal eye, and its weight = 0. That 

 would mean that two of the fundamental sensations of the normal 

 eye would, to the colour-blind person, be excited to equal strength 

 by all exciting causes. In fact, it has recently become probable 

 that the solution of the enigma is to be sought in this direction. 



The older attempts to explain colour-blindness proceeded from 

 the first-named assumption, that one of the fundamental sensa- 

 tions was wanting to dichromic eyes. I myself have adopted 

 this in the first edition of this hand-book*. 



As Helmholtz is not a person to use language incon- 

 siderately in such a case as this, we may gather much 

 information from this short passage. In the first place he 

 makes it clear that the original hypothesis was not in- 

 tended as a positive and definite explanation. It was only an 

 "attempt to explain," and it is now characterized as "alt" 

 (old) , a word which, as I understand it, does not here mean 

 simply early in time, but carries with it the idea of "aged," 

 " ancient," " antique," " stale," something superseded by 

 " new." The expression often recurs with clearly this 

 meaning. Then the explanation of colour-blindness is called 

 an "enigma" ; it is still obscure, and wanting "solution/' 

 . And thirdly, the passage states that in consequence of some 

 recent events a new solution has become probable in a 

 certain direction. The recent events alluded to have been 

 clearly the more complete evidence acquired as to the facts 

 of dichromic vision ; and the new solution, which indeed is 

 already indicated, will be better explained by and by. 



It is difficult to construe all this otherwise than as intimating 

 that the author does not now attach much weight to the 

 former explanation, and we shall find, farther on, abundant 

 confirmation of this interpretation. 



He, however, thinks it right to reprint the part which 

 contains the " alteren Erklarungsversuche," but he adds now 

 the following new saving clause (p. 366) . 



Nevertheless (immerhin), as it appears doubtful what sensations 

 of the normal eye correspond to the two colour sensations of the 

 dichromic patients, Donders has recommended that, according- to 



* The important original passages are as follows : — 



" Das wiirde heissen, dass zwei der Grundemptindimgen des normalen 

 Auges dem Farbenblinden durch alle Reizmittel gleick stark erregt 

 wiirden. In der That ist es neuerdings wahrscheinlich geworden, dass 

 in dieser Richtnng die Losung des Rathsels zu suchen ist. 



" Die alteren Erklarungsversnche der Farbenblindheit gingen Ton der 

 erstgenannten Annahme aus, dass den dichromatisclien Augen eine der 

 Grnndempfindungen fehlte. Ich habe dies in der ersten Auflage dieses 

 Handbuchs selbst anoenommen," 



