Although the fact is well known that inoculation of animals with the pneumococcus develops against subsequent inoculation with virulent cultures an immunity which is specific for the homologous type of pneumococcus, there is no record of a quantitative determination of the degree of immunity that is obtained after vaccination with standardized vaccine. Accordingly a series of experiments with the inoculation of mice with pneumococcus vaccines of types I, II, and III were made, the results of which it is the purpose of this paper to record.

Miss Thelma L. Franklin, of the laboratory staff, prepared vaccines of pneumococcus types I, II, and III according to the standard methods used in the laboratory and vaccinated mice with these vaccines. In order to test the protection obtained as a result of the vaccination, living, virulent cultures were inoculated seven days after the last dose of the vaccine.

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Presented by title at the Twenty-first Annual Meeting of the American Bacteriologists, Boston, Mass., December, 1919.

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