The idea of replacing by transplantation, in eases of leukoma, the opacified part by a graft of transparent cornea, is one which has occupied the energies of ophthalmologists for a long time. It is now nearly a century since Riesinger first undertook this task. Without entering into historical details, it will be sufficient to mention that the corneas of animals, as well as various transparent substances, from small round pieces of glass or celluloid to membranes of fowls' eggs, have been tried. Numerous difficulties and disappointments have cooled the ardor of experimenters and finally it was found that inert substances always acted as foreign bodies and were eliminated more or less rapidly. On the other hand, trials of heteroplasty, that is to say, of lower-animal tissues transplanted on man, had no better success in the cornea than the transplantation of glands or the transfusion of blood. The progress of modern