This is an affection known as Daltonism, from the man who first described it, and is more common than is generally supposed. Persons suffering with this difficulty are unable to distinguish red, green, or other colors. In some cases, only the form of objects are discerned, all appearing of the same color. The affection is much more common in men than in. women. Great harm may result from this defect, which exists in this country to the extent of about forty per cent of the whole male population. It is especially dangerous in persons employed as pilots or engineers of railroad trains. It is an interesting fact worthy of notice that the color which the patient is unable to discern appears to him to be gray. It is probable that color blindness is in part, at least, due to the want of proper education of the eye in discriminating colors in early childhood. The defect is in many cases hereditary. It has been recently announced that colorblindness may be corrected by means of a pair of spectacles composed of two plates of glass between which is placed a thin layer of fuchsine.