MOST OF the early investigators of corneal transplantation used circular corneal grafts. Von Hippel1 introduced a corneal trephine and fathered a style of keratoplasty. Elschnig2 and Filatov3 adopted von Hippel's general technic and added modifications of their own invention. Thomas,4 who introduced corneal transplantation to England, used square corneal grafts in his early experiments on rabbits, but later abandoned this procedure in favor of the circular type. Thomas described a tendency of the corners of the square graft to protrude, and even become detached; he also found that one of the loops of the suture frequently came to lie in the incision, thus preventing proper union of the wound. Castroviejo likewise introduced corneal transplantation to the United States. Working at the Mayo Clinic in 1931, he5 initially performed corneal transplantations on rabbits, following the technics of Elschnig and Thomas; but these operations were all failures.