It is a very remarkable fact how many people who are defective in colour vision pass through a good part of their lives without being definitely aware of it. It is very doubtful whether, in the majority of cases, they themselves discover it. They may quite possibly attribute the descriptions of colour which they hear, and which appear to them absolutely false or meaningless, as due to mental or moral defects in their friends. I have had two cases of this recently. One was a gentleman of seventy-four, who had no conception that he had anything but normal colour vision; his daughters, however, had a suspicion that something was not quite right in it, and after a good deal of persuasion brought him to me to examine. The first mistake that he made was to state that he was sitting on a black velvet chair, whereas the seat was a deep crimson plush. He laughed at his daughter’s description of the mistake he made, and declared he was only colour ignorant, and that she was the one who was colour blind. The examination showed that colour ignorant he was, but that the ignorance was due to complete red-blindness. For the seventy-four years he had lived he was unaware of his deficiency, suspecting it in others, and it was only an accidental circumstance which made him acquainted with the true state of his colour perception. Another elderly gentleman, in a high position in life, was also accidentally tested, and he proved to be completely green-blind. He, too, was quite unaware of his defect, and protested that, yachtsman as he was, he would never mistake a ship’s lights; but a very brief test showed his friends who were with him that his declaration had to be received with a certain amount of reservation. Others there are who certainly do know that some peculiarity exists in their sense of colour, and, foolish as it may appear to be--though, after all, it is quite consistent with a sensitive nature--they have tried to hide their defect from their fellow-creatures. Such examples, no doubt, some of my audience have met with, and experience tells me that they have just as much reluctance to pass an hour in my darkened room as they would have to occupy a police cell. In those few cases that have come voluntarily to me for examination, the peculiarity in colour sense was first brought to notice by the patient--if patient I may call him--failing to distinguish between cherries and the cherry leaves, or strawberries and the strawberry leaves. Such mistakes committed publicly are usually the source of unbounded merriment and curiosity to schoolboys when made by their schoolfellows, and I am bound to say that even persons of graver years are not unapt to be amused at what they consider to be a shortcoming in their fellow-creatures. To the student of colour vision the discovery of curious cases of colour deficiency is looked upon in a very different light--a good case of colour blindness, or still better