In presenting the subject which I have chosen for your consideration today, I shall depart somewhat from the traditions of the section, and invite your attention to a purely medical topic. Some years ago in an effort to collect a large number of tonometric readings in order to determine the average normal tension of the eyeball, I had the tension taken of the eyes of all the patients in the hospital and outpatient department, whenever possible. Among this number were six cases of brain tumor. Some time later when compiling the histories of the brain tumor cases, I observed that when the amount of the choked disk was the same in the two eyes, the tension was equal or nearly so, and when the swelling was greater in one eye than in the other, the tension was different in the two eyes, being least in the one showing the greater