This paper presents an experimental comparison of the effect of heating of the immunization material upon the antibody-invoking effectiveness of the type-specific (SP) and species-specific (P) antigens of Type II pneumococci. Heating of the pneumococcus suspension (vaccine) invariably decreased the production of species-specific antibodies (anti-P) without a comparable effect upon the production of type-specific antibodies (anti-S).

For diagnostic typing purposes, the ideal antipneumococcus serum should contain the maximum content of type-specific, and the minimum of species-specific antibody. Our results with forty-one rabbits indicate that the ideal serum from the type-specific standpoint would be obtained by immunization with the heated cells of virulent pneumococci over a comparatively short immunization period; and that the only thing gained by continued immunization or by the use of unheated bacteria at any stage of the immunization, is an increase in the species-specific antibody which is undesireable in sera to be used for diagnostic purposes.

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