1. When mice are passively immunized by the intraperitoneal injection of antipneumococcus horse serum or actively by the injection of heat-killed pneumococcus cultures, and are then alcoholized and sprayed with a culture of pneumococci of the same type as that of the bacteria employed in immunization, a considerable number die with localized lesions in the lungs.
2. If instead of injecting immune serum of the type corresponding to that of the bacteria employed in producing the infection, normal horse serum or immune serum of a heterologous type be injected, or if the animals be previously immunized by the injection of killed pneumococci of a heterologous type, none of the animals which die show any evidence of localization of the infection in the lung.
3. The occurrence of pulmonary lesions in alcoholized mice after spraying with a culture of pneumococci is the consequence of a general immunity of a very mild grade.