The bacteriolysis by lysozyme was studied by measuring the light-absorption of a lysing suspension, with a Moll-extinctiometer. In addition to a morphological study, this procedure was applied to the determination of lysozyme, which could be made within 5 per cent, and to a study of the influence of pH and electrolytes. The optimal pH was found to be about 6.2. The optimum is caused by an interaction of two factors: at lower pH's the action of lysozyme increases, but below pH 6.2 the visible lysis is inhibited. The same is the case in distilled water, where a phenomenon, analogous to Nakamura's alkali-phenomenon was found. High concentrations of electrolytes inhibit the primary reaction, adsorption of lysozyme. In this respect the valency of the ions is predominant. Some general remarks are made on the importance of electrostatic forces in similar reactions.