1881.] How do the Colour-blind See the different Colours? 303 



persons, say as yellow, or, on the other hand, is a colour of which we 

 in general have not the slightest conception. 



If a theory of colour-blindness has for its object to explain the 

 different links in the chain of causes and effects, of which the first is 

 the objective light, and the last the subjective perception thereof, we 

 must first know this last. 



From the points of view of the different theories, different opinions 

 have been entertained on this subject, but practical proofs have 

 hitherto been wanting for them all, and, what is worse, the hope of 

 ever gaining a solid basis for such proofs has been given up, for the 

 reason that they must be found in the subjective perception of another 

 man. 



Since it is impossible for one person to make himself master of that 

 conception in another, we cannot even objectively prove that all normal- 

 eyed persons see the different colours in the same way. Still it may be 

 assumed as an axiom that at least the quality of the different principal 

 colours is the same for all persons who show the same conception of 

 colours in general. Else we should not talk of colour, as all spiritual 

 communication would be impossible between persons whose sensuous 

 impressions were quite at variance. 



If that axiom is accepted, and we take for granted that all normal- 

 eyed persons see colours in the same way, as do also the colour-blind 

 of the different sorts in their own particular manner, I will endeavour 

 to show that the question which stands at the head of this article is 

 not only not impossible to answer, but that I can already give that 

 answer, furnished with scientific and objectively binding proofs. 



There is apparently but one way to establish such an answer. A 

 normal-eyed person must, while retaining his own colour-sense, be put 

 in position to see with a colour-blind eye, and compare the impressions 

 on that with those on his own normal eye. He cannot use either the one 

 or the other unless they stand in a living organic communication with 

 his own brain. He must, so to speak, grow into the colour-blind and 

 his chromatic sense without losing the use of his own. 



Such a phenomenon, which here is a conditio sine qua non, it is, of 

 course, impossible to procure in an artificial way ; but still I will show 

 that an organic combination of a normal and a colour-blind eye with 

 the same brain is not impossible to be realised in a perfectly natural 

 manner. 



Congenital colour-blindness is, as is known, in most cases inherited, 

 and inherited according to definite laws. (Vide Frithiof Holmgren : 

 "La Cecite des Couleurs en Suede," p. xm.) One of these laws is, that 

 all the children of the same parents are not afflicted with this defect ; 

 some are free. Nor is the colour-blindness of the same degree in those 

 affected. Accordingly it would seem not to be contrary to the laws of 

 inheritance that a person should be born with one normal eye. while the 



