of Colour -disease. 93 



saying that 



Messrs. B and F are blind to potassium-red, 

 Mr. M blind to potassium-blue, 

 Mr. L blind to strontium- and potassium-red, — 

 a designation which, in spite of its length, has the advantage of 

 being absolute and independent of the instrument. 



All these gentlemen I investigated five years ago, and have 

 described them in v. GrafVs Archiv. They are selected because 

 they represent all classes : for Messrs. B and F are plane Dal- 

 tonists, and therefore colour-mistaken ; Mr. L a linear Daltonist, 

 and therefore totally colour-mistaken ; Mr. M not at all colour- 

 mistaken, but only colour-blind. 



For the sake of intelligibility, some communications on sensa- 

 tional colour- mi stake, that second great division of colour- dis- 

 eases, may be permitted to me. 



The first kind of colour-mistake which I investigated, and first 

 in my own case, concerned what I have called " violet vision"* 

 in the advanced santonine-narcosis, in which all objects, the 

 darker they are or are illuminated, the more violet do they 

 appear. It is often combined with violet-blindness ; and yel- 

 low vision with violet vision. If this is so, the following striking 

 experiment t can often be made: — " One who does not see the 

 blue end of the spectrum thinks a homogeneous yellow common- 

 salt flame seen through a homogeneous yellow glass to be yel- 

 low ; seen through three or four such glasses, to be violet." 



Hence there is a complete inversion of the three fundamental 

 constituents of the perception of a colour — perception of purity, 

 tone, and strength. This experiment shows that such a person 

 confounds two opposite complementary colours of unequal inten- 

 sity, and considers two unequal intensities of one tone of colour 

 to be opposite colours. This is only one example of the nume- 

 rous confusions of colour which occur in the santonine intoxica- 

 tion in the case of violet vision, but it is the characteristic one. 

 If a couple of confused colours have been determined by mea- 

 surement, the others may be calculated beforehand, to which I 

 will here only advert J. 



Formerly I called those who thus systematically confound 

 colours colour-confounders j I would rather now call them colour- 

 mistaken, not merely for shortness' sake, but also because healthy 

 people, according to the degree of illumination, confound colours, 

 though but few ; colour-blind people still more; and the charac- 

 teristic of the colour-mistaken as compared with them consists 

 in a further mistake in the designation of the colour. 



* Virchow, vol. xix. p. 532. 



f Virchow, vol. xx. p. 278. A strontium -spectrum (case 45) appeared 

 to consist of purple, violet, and green ; when looked at through a dark 

 blue glass, only of green. J Virchow, vol. xx. p. 245. 



