It is well known that a small percentage of the people in this country, and perhaps in all countries, are more or less colour-blind, and it is a noteworthy fact that such persons are often entirely unconscious of it or do not fully appreciate its disadvantages. The officials of the railroads and certain other corporations test the applicants for situations, and if they are found to be colour-blind, or not able to distinguish colours accurately, they are not employed. It will be readily seen that if a railroad engineer or the officer of the deck on one or our large passenger ships could not distinguish between red and green signal lights in the night, most disastrous accidents might be the result.