of Colour -disease. 89 



disappear. By interposing a cobalt glass, which only leaves the 

 ends of the spectra, we can be easily convinced of this. The 

 third violet lies then between the second violet and the second red. 

 Since then, I have experimented upon colour-blind people by 

 allowing them to look in the dark room at the spermaceti light 

 through two parallel gratings (with 50 to 100 lines to a millimetre) 

 at the distance of distinct vision, and then allowing them to de- 

 scribe or, still better, draw what they saw. The interposition of 

 a slit was useless. 



I found now*, and first of all in my own casef, that, while 

 healthy persons see two dark spaces on each side of the light, 

 persons seeing ultra-violet see only one; and colour-blind see 

 three, four, and even six. It was easy to show this in the case of 

 colour-diseased persons of all kinds. 



A person suffering from jaundice from acute atrophy of the 

 liver saw three J ; and this number was seen by a sick person with 

 gastro-duodenal catarrh and jaundice, and by a person with chro- 

 nic enlargement of the liver, jaundice and albumenuria. A patient 

 with cancer of the liver and jaundice saw four§. Among the 

 Daltonists 



some saw two (Messrs. A, C, E, F, J); 

 some three (Messrs. B, D, H); 

 others four (Messrs. G, M); 

 others five (Messrs. K, 0); 

 one six (Mr. L)||. 

 . All these patients, of whom many were investigated at totally 

 different times, exhibited a constant colour-blindness. It is 

 otherwise in the santonine intoxication, as was probable from pre- 

 vious investigations. During narcosis the number of spaces rises 

 and falls from two to 



three (cases 46, 50, 51, 56); in other experiments to 

 four (cases 44, 45, 57); in some, finally, to 

 five (cases 43, 46), and in one case to 

 six (case 49) %. 

 From these results it might appear as if there were colour- 

 diseased persons who are not colour-blind. But I have pointed 

 out in 1860 that the limitation to two intervals is no proof 



* " On Colour-blindness by taking Santonic Acid," Virchow's Archiv, 

 vol. xix. pp. 522-587, and vol. xx. pp. 245-291. 

 t Ibid. vol. xix. p. 524, case 40. 

 X Ibid. vol. xxx. p. 444. § Ibid. p. 443. 



II The examination of Daltonists is found in a paper on permanent visual 

 delusions in v. Grafe's Archiv fur Ophthalmologic, vol. vii. pp. 72-109 

 (1860). 



51 The cases are numbered throughout in the various papers in "Virchow's 

 Archiv. From 52 downwards they are found in vol. xxviii. pp. 30 to 82 in 

 " Hallucinations during Santonine intoxication." 



