In the experiments described in the previous paper (Kalvin et al [1966],1cupping of the optic disc and atrophy of the optic nerve were found after moderate to severe elevation of the intraocular pressure (>40 mm Hg) which lasted longer than 36 hours. Although evidence was obtained on the site of action of the α-chymotrypsin and on the conditions necessary to produce the optic nerve changes, still, the pathogenesis of these changes was not determined. The following observations indicated that the changes could be related to alteration of the blood flow pattern to the glaucomatous eyes: The rapidity of development of the optic nerve changes. Macrohemorrhages and microhemorrhages in the optic disc, and in and around the optic nerve. Peripapillary retinal edema. Nasal displacement of the blood vessels on the optic disc. Engorgement of the retinal veins. Thus, the present experiments were performed to