a portrait by candle-light, used yellow for pink in laying on his flesh tints, with a pleasing result that may be readily imagined. In fact, the instances of colour-blindness mentioned by physiological writers are almost innumerable, and I should only weary my readers if I related all the authentic cases of this singular affliction. One instance, however, which was very carefully observed by Wartmann, a distinguished German oculist, merits our attention. The afflicted person, whom Wartmann speaks of as D., was thirty-three years old. Those of his brothers and sisters whose hair was fair suffered from the same infirmity, but those whose hair was dark were exempt from it. Like so many others who are colour-blind, he could not distinguish between cherries and their leaves, and confounded a sea-green piece of paper with a scarlet ribbon placed near it. A rose of the ordinary hue appeared greenish-blue. Being anxious to see if reflected, refracted, and polarized light exercised a different action on his retina, Wartmann tried him first with the prismatic spectrum, but he could only distinguish four colours,—blue, green, yellow, and red. He could distinguish perfectly the peculiar black lines seen crossing the spectrum in certain places, and known by the name of Fraunhofer's lines. He then placed in his hands thirty-seven pieces of differently coloured glass, but he could only distinguish four varieties. The colours produced by polarized light seemed to give the patient quite as much trouble as those produced in the ordinary way. Chocolate brown appeared reddish brown; purple, dark blue; and violet, a dirty blue. When colours were illuminated by sunlight, they seemed to him to be redder than usual, even green and blue appearing red.
In considering cases of colour-blindness, it is very difficult not to be misled into using wrong terms, as applied to colour, for we have no possible means of knowing what colour it is that is really seen by the patient.
