The detection of colour-blindness from a practical point of view / by F. W. Edridge-Green.

  • Fredrick William Edridge-Green
Date:
1889
Catalogue details

Licence: Public Domain Mark

Credit: The detection of colour-blindness from a practical point of view / by F. W. Edridge-Green. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    tingiiish between brown and green by the touch, but not by the colour. Again, many colour-bHnd persons will pick out a large number of green wools leaving one or two in the pile. An inexperienced examiner may at once pass the candidate. Should he not do so, he is placed in an awkward situation if the candidate refuse to pick out any more wools, saying there are no more like the test green. He has put no confusion colours with the test green, but only greens. Holmgren suggests that, under these circumstances, the examiner should take one of the greens which has been overlooked, and one of the con- fusion colours, and ask the candidate which two out of the three are the most alike. I contend that this is not a fair way of examining, because the answer to the question so much depends upon the point of view from which the wools are regarded, namely, which is the examinee likely to be influenced by—the shade or the colour. Uneducated persons always find a difficulty in matching shades of colour, and they will often answer, Neither is much like the test. Under any circumstances, an uneducated and unpractised colour-blind is under a disadvantage compared with an individual who is educated and practised in colom's. A pm-e green is one of the worst possible colours to choose for a first test, because, in the five, four and three- unit, the green is simply enlarged. Therefore, if the blue- greens be removed, these colour-bhnd may easily pass through the test without detection. T'win CoZozws.—Stilhng's plates, Cohn's worsted letters, Bonder's discs, and Grossman's method are included under this head. The method of employing twin colours is useless, because there are different degrees of colour-blindness. Thus deal- ing only with the two-unit, we may have a spectrum of normal length, or the red or violet end may be shortened in a variable degree. If, for instance, we had twin letters of red_ and green made with colours selected by a two- unit with an unshortened spectrum, on examining a two- unit with considerable shortening of the red end of the spectrum we find that he can read the letters with the greatest ease, because the red portion (on account of a large number of rays not being perceived) would appear much darker than the green. In the same way combina-
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