Intradermal lesions and subsequent bacteremia were produced in rabbits by the intradermal inoculation of Type III strains freshly isolated from pneumonia cases. Slight intradermal lesions were produced but no bacteremia was found in rabbits inoculated with an old stock Type III strain.
The intradermal lesions and the bacteremia produced by the inoculation of Type III cultures in rabbits were usually less severe than those produced by the inoculation of Type I culture.
The bacteremia in rabbits was checked and the rabbits protected by suitable amounts of Type III concentrated antiserum given intravenously 24 hours after the infecting dose.
The amount of Type III antiserum necessary to protect rabbits inoculated intradermally with virulent Type III cultures was not appreciably greater than the amount of Type I antiserum required to protect against Type I.