CASE 48.--Mr. B--, æt. 32, first observed the occurrence of diplopia at the beginning of April, 1877. Myopia 6 D. is present in both eyes, visual acuteness on the right 1/2, on the left rather more than 1/2 (5/9). The double images are homonymous and sometimes (not always) move farther apart at the limits of the visual field. Patient could only decide after two years, in July, 1879, on the operative treatment then proposed. Diplopia continued to exist; single vision was only now and then possible for a short time. On correction of the myopia (if one eye is provided with a red glass) prism 12° suffices for union of the double images. If one visual field is moved in a vertical direction by a prism of 5° during the trial of convergence, prism 38° is necessary in order to equalize the lateral deviation of the double images, and to place them perpendicularly above one another for an object 5 m. distant. On July 14th, tenotomy of the internal rectus of the left eye; single vision next day on correction of the myopia, prism 6° is overcome by divergence; if, however, double images are produced by a vertically deviating prism of 5° they immediately show homonymous lateral deviation, which is corrected by prism 18° at a distance of 5 m. Two months after the operation the diplopia was certainly better, but by no means removed; squint occurred periodically as before, so that sometimes single vision was possible at 3 to 4 m., sometimes troublesome diplopia was present. During the test of convergence with prisms deviating in a vertical direction, a prism of 38° was necessary for the equalization of the lateral deviation just as before the operation. Therefore in the middle of October the internal rectus of the right eye was divided, and the conjunctiva loosened as far as the caruncle. Three days afterwards single vision, facultative divergence = prism 5°; in the trial of convergence, equalization by means of prism 8°. In the middle of October, two months after the operation, diplopia had not appeared again; facultative divergence = 0; homonymous double images are produced by a red glass before one eye, slight convergent deviation on covering it, which in the trial of convergence is equalized by prism 20°. The preponderance of the interni was now so far lessened for the ordinary use of the eyes, that permanent binocular single vision was possible.