EXPERIMENTAL PNEUMONIA IN MICE FOLLOWING THE INHALATION OF STREPTOCOCCUS HÆMOLYTICUS AND OF FRIEDLÄNDER'S BACILLUS

The results of these experiments support the previous observations that mice react in different ways to the inhalation of different bacteria. If normal mice are sprayed with hemolytic streptococci or Friedländer's bacillus, these organisms may be recovered from the lungs and heart's blood for a number of days after exposure. A large number of mice so exposed die of a septicemia during the 30 days following spraying. Consolidation of one or more lobes is not rare. If normal mice are exposed to an atmosphere of pneumococci, however, the organisms rapidly disappear from the lungs and only an occasional mouse succumbs to pneumococcus septicemia. In order to cause the pneumococcus to invade, the mice must first be alcoholized. If mice are first alcoholized and then exposed to a pneumococcus atmosphere, the pneumococci persist for a longer time in the lungs and a number will die of septicemia, a state of affairs which resembles that seen after the administration to normal mice of the other two organisms studied. In order to produce pneumococcus lobar consolidation, however, the mice must be first partially immunized and then allowed to inhale the organisms while under the influence of alcohol. A large percentage of both the normal and immune mice so alcoholized die within 5 days of exposure. There also appears to be a definite relation between the mortality and the length of time inspired bacteria persist in the lungs. Whether this lag in removal allows multiplication of the bacteria and massive infection to occur has not been determined. Following inhalation of pneumococcus, the organisms were either removed rapidly and without apparent detriment to the animal, or, as in the case of the alcoholized mice, invasion occurred, in which event the mouse usually succumbed rapidly, localization in the lung only occurring in partially immune animals. In the case of the hemolytic streptococci and Bacillus friedlænderi, however, the whole process of removal and infection seems to be slower. Infection and pneumonia occurred more often. These organisms seem to possess much greater invasive power when inhaled than the pneumococcus, though on intraperitoneal or subcutaneous inoculation, pneumococcus is highly virulent for normal mice.