1. Pneumococci possess an active intracellular enzyme which causes lysis of heat-killed pneumococci of the same and heterologous types and to a less degree of a closely related organism, Streptococcus viridans.
2. The optimum reaction for lysis lies between pH 6 and 8.
3. The bacteriolytic action is proportional to the concentration of the enzyme.
4. Heating the enzyme for 30 minutes at 60°C. destroys its activity.
5. The possible relation of the enzyme to autolysis is discussed.