(j) The operation valuable as a prophylactic measure. DR. ROBERT H. ELLIOT, F.R.C.S., Lieut.-Col. I.M.S., Madras, India. Discussion by DR. FRANK C. TODD, Minneapolis. V. Operations Other than Scleral Trephining for the Relief of Glaucoma. Abstract:-- Most of the ordinary surgical procedures employed for lowering intra-ocular tension furnish a permanent cure of certain fairly well defined varieties of glaucoma. They also relieve the symptoms and retard the progress of other varieties of the disease, even if they do not perform a cure. In a third class of cases, they either have no effect whatever in arresting the disease or they hasten its march towards blindness. What operative procedure gives, on the whole, the best results? In other words, what operation is the easiest of performance, is the least likely to be attended by serious complications and is available for the largest number of cases? Reasons for believing that of the better known procedures simple iridectomy is the least effective, while those interventions producing a large, thin, scleral filtration-cicatrix are the most valuable. DR. CASEY A. WOOD, Chicago. Discussion by DR. A. E. BULSON, JR., Fort Wayne Etiology and Classification of Glaucoma BY EDWARD JACKSON, M.D., Denver. It is convenient to start with the conception that glaucoma is increased tension of the eyeball, plus the causes and effects of such increase; although a broad survey of the facts may reveal a clinical entity to be called glaucoma, without increased tension constantly or necessarily present, and cases of increased intra-ocular tension not to be classed as glaucoma. The physiologic tension of the eyeball is essential to ocular refraction, and closely related to ocular nutrition. Fully to understand the mechanism for its regulation would carry us far toward an understanding of the causes of glaucoma. Normal tension is maintained with a continuous flow of fluid into the eye and a corresponding outflow. Complete interruption of the nutritional stream would be speedy death; partial interruption may be held responsible for most of the visual impairment and pain of glaucoma. The balance of intra-ocular pressure is not maintained by the slight distensibility of the sclero-corneal coat. Increased pressure does not open new channels for the escape of intra-ocular fluid; if, indeed, it does not tend to close the normal channels.