The intravenous injection into rabbits of suspensions of dead T. pallidum derived from rabbit testicular chancres regularly caused the appearance of Wassermann and flocculation antibodies in significantly increased titer. Control suspensions of cultured treponemes (Reiter strain) added to extracts of normal testes were ineffective. This suggests that the Wassermann and flocculation reagin elaborated during syphilitic infection may be an antibody to T. pallidum which happens to cross-react with alcoholic extracts of mammalian tissue.

The antisera did not cause the agglutination of suspensions of pathogenic T. pallidum, living or dead, did not give specific complement fixation with those suspensions, and did not usually cause the living treponemata to lose their infectiousness.

Animals immunized with such aqueous suspensions for as long as 4 months, or with organisms suspended in a water-in-oil emulsion, were not demonstrably resistant to infection. As few as ten living organisms inoculated intradermally into animals "immunized" with as many as 38 billion dead treponemata regularly produced typical darkfield positive infections; and two of five animals inoculated intratesticularly with ten organisms were also infected.

The contradiction involved in the production of antibodies cross-reacting with a non-specific antigen, and the non-appearance of specific antibodies against the organism used as antigen, is discussed in the text.

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