1. The administration of alcohol produces no evident histological changes in the lungs of mice.
2. Following inhalations of pneumococci the organisms are not visible histologically in the lungs of mice either in the bronchi or alveoli.
3. In partially immunized mice which have been exposed to a pneumococcus spray while alcoholized, true lobar pneumonia not infrequently develops.
4. The primary lesion of such lobar pneumonia in mice is an interstitial inflammation of the alveolar wall and the infection spreads in the interstitial tissue like a cellulitis.
5. A tentative explanation of the "lobar" distribution of pneumococcus pneumonia is offered.