Moreover, there are the =osseous=, the =cartilaginous=, and the =opaque cataracts=; but those distinctions rather concern the anatomist than the pathologist, as they may be guessed at, yet are not to be distinguished with certainty one from another, during life. That which more concerns the reader is, to learn the manner, if possible, of preventing cataract from disfiguring his horse's eyes. Then will the gentleman be kind enough to hold a sheet of white paper close to his nose, so that the eyes may see nothing else, for a single half hour. Let us suppose the trial has been made. With many people the head has become dizzy and the sight indistinct. In some persons singing noises are heard and a sensation of sickness has been created. Let the author strive to explain this fact. Travelers, passing over the Alps, wear green veils, to prevent the strain or excitement which looking upon a mass of white snow occasions the visual organs. Any excitement is prejudicial to the eye. Workers at trades dealing in minute objects, often go blind, and the use of the microscope has frequently to be discontinued. But to look continuously upon a white mass is the most harmful of all other causes. This fact must be considered as established. And what does the horse proprietor have done to his stable? He orders the interior to be whitewashed. It looks so clean, he delights to see it; but do the horses--does nature equally enjoy to look upon those walls of "spotless purity?" Before those walls, with its head tied to the manger, stands the animal through the hours of the day. Close to its nose shines the painful whiteness which the master so enjoys. Is it, then, surprising (seeing how nature for its own wise purposes has connected all life) that the equine eye, doomed to perpetual excitement, sometimes shows disease? A horse with imperfect vision is a dangerous animal. A small speck upon the lens confuses the sight as much as a comparatively large mark upon the cornea. To render this clear, let the reader hold a pen close to the eye; it prevents more vision than yonder huge post obstructs. So impediments are important, as they near the optic nerve. The lens is nearer than the cornea, and therefore any opacity upon the first structure is more to be dreaded.