Mackenzie, in his treatise on ophthalmology, first directed especial attention to the fact that, in some persons, tobacco exerted a toxic influence upon the optic nerve. This view was fully confirmed by the observations of Hart and Wordsworth, published a few years later. Hutchinson followed with several series of cases published in succeeding volumes of the Ophthalmic Hospital Reports. Each succeeding series being studied in the light of the preceding ones, threw an increasing flood of light upon the varying phases of this interesting affection. Krenchell, in 1870, gave us an excellent treatise upon this subject, based upon the careful study of 183 cases observed in Hanson's Copenhagen clinic. Forster and Leber, in 1868-69, published their method of correcting slight defects of vision by means of the color sense. Bjerrum discovered the value of using slightly different shades of the same color in detecting the slighter degrees of central scotoma.