The concept of the relation of even small changes in the hydrogen ion concentration to vital biochemical and biophysical processes has stimulated many studies on the acid-base equilibrium in various body fluids and tissues. The interest of ophthalmologists has been focused mainly on one phase of this relation, that is, the changes in the turgescence of colloids due to a shift in the hydrogen ion concentration. Its possible bearing on the problem of glaucoma was considered by Fischer1 and was later the basis for experimental work on the ph volume curve of the vitreous (Baurmann and Thiessen,2 Duke-Elder,3 Goedbloed,4 Salit and O'Brien,5 von Sallmann6 and others). No experimental work in ophthalmology, however, has been reported on the relation of the ph of the milieu to the optimal action of various enzymes, such as tissue proteinases (cathepsin and peptidases) and the proteolytic enzymes