In the course of an investigation into the “Present State of Knowledge and Opinion in regard to Colour-blindness,” it was found necessary to search for many data illustrative of various matters connected with the phenomena of the defect. These were obtained from a great variety of sources, chiefly from foreign publications not easily accessible; and as it was highly desirable to bring them forward in evidence, showing their bearing on difficult and controverted points, the plan has been adopted of collecting in this place the most important extracts, and of arranging them in a convenient manner for reference.