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KNOWLEDGE AND OPINION IN REGARD TO COLOUR-BLINDNESS. 45 



in which the red and green sensations had disappeared, while the yellow and blue 

 sensations remained. Two cases were given, and the conclusions were summed up in the 

 very positive terms quoted in "Data," letter B. 



Leber, in 1869, wrote a long article on Anomalies of Colour- Vision by Disease, and 

 in 1873 a further article, in which he fully recognised their connexion with colour- 

 blindness, and pointed out the positive sensations of j^ellow and blue as opposed to the 

 theoretical assumptions. 



Dr Berry also, in his Paper of 1880, on Central Amblyopia, speaks of many cases 

 where the diseased part imitates congenital colour-blindness. 



Von Kries, 1882, gave a general account of this kind of affection; — see "Data," 

 letter C. In this green became yellow or grey ; red could not be distinguished from 

 yellow ; all was blue, yellow, or grey. Whenever red failed, green failed also. 



Uhthoff, 1887, investigated many cases more elaborately, one of them being 

 examined by Dr Konig with spectral colours. The results were the same. See " Data," 

 letter D. 



All these numerous cases showed an almost perfect analogy with the congenital 

 dichromic vision ; and in none of them was there any doubt as to the true correspondence 

 of the two colours with the normal yellow and blue. 



Colour-Blindness of One Eye only. 



Another mode of checking the testimony of the colour-blind was the discovery that 

 there were some rare cases of individuals who had normal colour-vision with one eye, and 

 abnormal with the other. The earliest were mentioned by Niemetschek in 1868, and 

 Woinow in 1871 ; but these were open to doubt. Becker substantiated a case in 1879, 

 but in this the abnormal eye saw only light and shade. See " Data," letter E. 



At length, in 1880, Von Hippel discovered the case of a young man whose left eye 

 was perfectly normal, while his right eye had dichromic vision. On comparing the vision 

 of the two eyes, positive evidence was obtained that the dichromic sensations accurately 

 corresponded with the normal yellow and blue. Some critical remarks made on it 

 prompted Von Hippel to repeat his observations with the greatest care : he showed the 

 patient the pure spectral yellow and blue, and they, as well as the white, appeared 

 absolutely alike with both eyes. The neutral line for the dichromic eye was between b 

 and F. For further details, see " Data," letter F. 



Professor Holmgren also examined this case, and was so impressed with it that he 

 wrote a Paper on it for the Koyal Society of London, which he did me the honour to 

 ask me to present. It was read at the Society on 13th January 1881, and is published 

 in their Proceedings, vol. xxxi. p. 302. It was entitled, " How do the Colour-Blind see 



