1. The systems responsible for oxidation and reduction in the pneumococcus cell have been shown to consist of two components, the nature of which has been discussed.
2. The oxidizing and reducing power of active extracts of pneumococci is inactivated by exposure to air. This loss in activity is due to an inactivation of the thermolabile cellular component consequent on secondary reactions analogous to those which under similar conditions destroy the hemotoxin and enzymes in pneumococcus extracts.