of Colour-disease, 97 



Mr. K, 



49. O 0+=U 42 + 



50. O 30- =TJ 68 + 



51. 60-=U 54 + 



52. 90- =U 43 + 



It is thus seen that totally colour-mistaken people are not so 

 exact in adjusting as the singly colour-mistaken, — possibly from 

 a little hastiness if they are tired by the investigation, but 

 partly from amblyopia and atrophy* of the visual nerve, which 

 probably always accompanies so high a degree of colour-disease. 

 This is also seen in the circumstance that the position of the 

 lower Nicol varies within certain limits. 



These cases can thus be characterized by a group of equa- 

 tions which indicates the results for both limits, and a mean 

 value of the lower Nicol ; thus, for instance, for 



fU-30 = O + 89- 



Mr. L, \ U-45 = + 16- 



IJJ-60 = O- 6 + 



fU + 30 = O±90 + 



Mr. OA U + 45 = O + 20- 



[11 + 60 = 0- 9 + 



Remembering that Daltonists may be at the same time colour- 

 blind — indeed blind to red and to violet, and both to different 

 degrees — it is easy to conceive that no Daltonist sees colour 

 exactly like another, and what different perceptions of colour the 

 same excitation must produce in different individuals. 



Among fifty-nine colour-diseased I have not found any two 

 who exactly exhibit the same sense of colour. 



It seems almost a matter of course, and it follows, indeed, 

 from other experiments and reasoning, as 1 showed some years 

 agof, that Young's theory of colour, whether modified or not, is 

 irreconcileable with this ; for it only allows three kinds of colour- 

 blindness, or, taking in the combinations, six. 



'* This is the reason why I am not certain whether Mr. K is affected in 

 the same way as Messrs. L and O ; for each time I have had to abstain 

 from further investigation. 



t Grafe's Archiv, 1860, p. 89; and Virchow's Archiv, vol. xx. p. 282. 



