SIGHT AND HEARING OF RAILWAY EMPLOYES. 435 



all its details if he but remember that upon the blanks submitted to 

 him for his action must appear only odd numbers, and that if the even 

 ones are mingled the case is one of color-blindness. 



DR. THOMSON'S COLOR-TEST. 



For the acuteness of vision the best and most simple method is to 

 employ letters of known size at given distances ; and, as we might 

 meet with men who could avail themselves of opportunities to learn 

 by heart those of " Snellen," ordinarily used, the writer had a rotary 

 disk constructed on the same principle, whereby but a few letters were 

 exposed to view, but many more could at will be brought into sight 

 when desired. For the hearing, a watch and the voice in conversation 

 were used. 



These instruments, together with the Rules and Regulations now 

 submitted to you, won the approval of the committee of railroad officers, 

 were put into practical use in two thousand preliminary examinations, 

 were adopted by the highest officers, accepted by the Board of Di- 

 rectors, and ordered to be put in force upon the entire road, under the 

 supervision of the writer as their surgical expert. His duties were to 

 assure himself of the accuracy of all instruments, to give instructions 

 to the examiners of the different divisions in their use, to give his 

 opinion upon any doubtful cases, their blanks being placed before him, 

 and to examine personally any men sent for the purpose, and to render 

 fit for service, by medical or surgical treatment, or by proper correct- 

 ing glasses, any capable of such relief. 



From an inspection of the blanks, and a knowledge of the men, the 

 Division Superintendent could deal with most of the cases by suspend- 

 ing or transferring them to other duties. The blanks of the color- 

 blind, and those much below the standard of vision, were transmitted 

 to the surgical expert, and, upon his advice, the men could be sent to 

 his office, where the color-blind were re-examined by the " stick " by 

 Holmgren's method, by that of Stilling, advised by the last Interna- 

 tional Congress, and by Donders's instrument, by which the lights of 

 the lamps and signals at night are so perfectly imitated in color, size, 



