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 Directors, 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 correcting 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 suspending 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 International Congress, and by Donders's instrument, by which the lights of the lamps and signals at night are so perfectly imitated in color, size,
