1. When mice are exposed to an atmosphere containing cultures of bacteria in the form of a fine mist, the bacteria readily penetrate into the lower respiratory tract.

2. Pneumococci which have reached the lung as a result of this procedure usually disappear within a few hours and give rise to no infection. Hemolytic streptococci, on the other hand, persist in the lung for a considerably longer time and a general septicemia usually follows.

3. Attempts to determine the conditions under which pneumococci which have reached the lung by inhalation may induce a local or general infection have not been successful.

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