. Color-vision and color blindness, a practical manual for railroad surgeons . ntains a rowof forty hooks, to which are attached by bangles fortytest skeins, arranged to be alternately match and con-fusion colors. The bangles are numbered in such a waythat odd numbers denote match skeins, and even niun-bers confusion skeins. The skeins from 1 to 20 cor-respond to Holmgrens first test, and consist of variousshades and tints of green alternating Avith confusioncolors,—grays, tans, light browns, etc. The second SELECTION TESTS. THOMSON S STICK. 67 series, from 21 to 30, is composed of liliter and
. Color-vision and color blindness, a practical manual for railroad surgeons . ntains a rowof forty hooks, to which are attached by bangles fortytest skeins, arranged to be alternately match and con-fusion colors. The bangles are numbered in such a waythat odd numbers denote match skeins, and even niun-bers confusion skeins. The skeins from 1 to 20 cor-respond to Holmgrens first test, and consist of variousshades and tints of green alternating Avith confusioncolors,—grays, tans, light browns, etc. The second SELECTION TESTS. THOMSON S STICK. 67 series, from 21 to 30, is composed of liliter and darkershades of rose alternating with bines, etc. Tlie thirdseries, from 31 to 40, is made up of reds alternatingwith browns, sages, and dark olives. In making an examination the candidate is re-qnested to select ten tints from the worsteds on the stickto match the liglit-green sample. The numbers attachedto the selected tints are recorded, and if the person liavea good color-sense his record will show none but oddnumbers between 1 and 20 ; while, if he be color-. FiG. 15.—Thomsons Stick. blind, the mingling of even numbers betrays his defectat a glance. In order to determine whether the defectis for red or green, tlie candidate is required to matchthe rose sample. The red-blind selects indifferently theroses and blues between 20 and 30, while the green-blind adds greens and grays. The third series, withred as the sample test, is used in the same manneraud corroborates the results obtained by the green androse tests. The record of each case is examined by theophthalmic surgeon, and any man fliiling to come up to 68 COLOR-VISION AND COLOR-BLINDNESS. the standard is given the benefit of a final examinationat the hands of the expert. This method, together witha test for vision and hearing, was subjected to an experi-mental trial on the Pennsylvania Railroad. Dr. Thom-son reports 1383 examinations among conductors, en-gineers, firemen, and brakemen ; 246 men were deficientin t
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Keywords: ., boo, bookcentury1900, bookdecade1920, booksubjecteye, bookyear1920
