Diseases of the eye : a hand-book of ophthalmic practice, for students and practioners / By G. E. De Schweinitz.

  • De Schweinitz, G. E. (George Edmund), 1858-1938.
Date:
1899
Catalogue details

Licence: Public Domain Mark

Credit: Diseases of the eye : a hand-book of ophthalmic practice, for students and practioners / By G. E. De Schweinitz. Source: Wellcome Collection.

Provider: This material has been provided by the Harvey Cushing/John Hay Whitney Medical Library at Yale University, through the Medical Heritage Library. The original may be consulted at the Harvey Cushing/John Hay Whitney Medical Library at Yale University.

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    The wools arc placed in a heap on a large table, covered by a light cloth and in broad daylight. A skein of the test-color is taken from the pile and laid far enough away from the others not to be confounded with them during the examination. The person examined is required to select other skeins from the pile nearly resembling it in color, and to place them by the side of the sample. He is made thoroughly to understand that he is recpiired to search the heap for the skeins which make an im- pression on his chromatic sense, and quite independently of any name he may give the color similar to that made by the test- skein. The examiner should explain that resemblance in every respect is not necessary; that there are no two specimens ex- actly alike; that the only question is the resemblance of the color, and that, consequently, the candidate must endeavor to find something similar in shade, something lighter and darker of the same color, etc. Test I.—The green test-skein is presented. The exami- nation must continue until the candidate has placed near the test-skein all the other skeins of the same color; or else, with these or separately, one or more of the skeins of the class of confusion colors, or until he has sufficiently proved by his man- ner that he can easily and unerringly distinguish the confusion colors, or gives unmistakable proof of a difficulty in accomplish- ing it. The candidate who places with the test-skein confusion colors (gray, drab, fawn, light pink, or yellow)—that is to say, finds that they resemble the test-color—is color-blind ; while if he evinces a manifest disposition to do so, though he does not absolutely do so, he has a feeble chromatic sense. Test II.—The rose-purple skein is presented. The exami- nation must continue until the candidate has placed all or the greater part of the skeins of the same shade near the sample ; or else, simultaneously or separately, one or more skeins of the confusion colors. If he confuses the colors, he will select either the light or deep shades of blue and violet, especially the deep, or the light and deep shades of one kind of green, or gray in- clining to blue. A candidate who is proven color-blind by the first test, and who in the second test selects only purple skeins, is incompletely color-blind. If in the second test he selects with