small patches, will inevitably show the defect in vision. With this end in view, I have had a set of brick-clay pellets some 3/16-inch in diameter, painted with water-colours mixed with soluble glass solution of the same colours as the wools. These are placed in a shallow tray, and presented to patients affected with this central colour blindness to pick out all the pellets which match reds and greens. They will tell you that they see neither one nor the other, though they will pick out the blue pellets unerringly. A red pellet they will match with a red, green, grey, or a brown one, and a green one with the same. If, however, you instruct them to direct their eyes a few degrees away from the tray, they will tell you they see all the colours, and as they endeavour to pick them out, they, with a natural instinct, direct their eyes again to the collection, when once more the colours vanish. It is almost piteous sometimes to see the distress which this simple test occasions. The sight of the colours for an instant and their immediate disappearance in the cases that I have tried, seem indicative of something terrible, for they usually have no idea of the cause of this (to them almost miraculous) phenomenon. I have seen these colour blind tested with a pair of ordinary bull’s-eye lanterns, placed side by side, with diaphragms of moderate size with coloured glasses, which can be changed at will, in front. At twelve feet distance they will often see both lights as one, but as they approach they will make out two lights and call them both white, or sometimes they will make a guess and call a green red, or _vice versâ_. It goes without saying that such eyesight is useless for reading signals, and indeed for any purpose whatever. Sometimes, but I believe this is rare, no colour whatever can be distinguished. CHAPTER XII. I will now give in full the result of the examination of a patient who was suffering from tobacco blindness. X., aged thirty-six, a commercial traveller, was suffering from rather severe tobacco amblyopia. The scotoma was a very marked one, and the loss of colour sensation most complete. Mr. Nettleship, who furnished the case, has kindly added the following remarks on the case:-- His acuteness of vision was 6/36 with the right eye and 6/60 with the left. He smoked half-an-ounce of “shag” daily and drank about four pints of beer. His sight had been failing for about two months. As is common in early stages of this disease the ophthalmoscope revealed no decided changes at the optic discs. He passed the test of the Holmgren wools satisfactorily, proving that the usual vision was normal for colour, but failed at once with the pellet test. [Illustration: FIG. 36.]