In a paper on hemiopsy, the author had shown that the parts of the retina affected with this disease were susceptible of luminous impressions and insensible to visual ones, and that the light by which they were impressed was derived by irradiation from the adjacent parts of the retina. The parts of the retina affected with hemiopsy were, however, so small, so irregularly distributed, and the phenomenon of such short duration, that it was difficult to study it and deduce any satisfactory results.