The observation of T. pallidum-like organisms reported by Collart, Borel, and Durel (1962, a, b, c, 1964) in the lymph nodes of both men and rabbits in seroreactive treated syphilis and the stimulating work of Smith and Israel (1967 a, b, 1968) on intraocular treponemes in late syphilis have created much interest in the survival and virulence of T. pallidum in tissues and body fluids in cases of untreated and treated, latent and late stages of seropositive syphilis in man. Research was

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... n with the aim of searching for and demonstrating virulent T. pallidum in the tissues and fluids of humans naturally infected with syphilis and of rabbits artificially infected with T. pallidum before and after adequate treatment with standard doses of penicillin. Attempts were then made to correlate the presence of T. pallidum with the persistent reactivity of the standard and specific serological tests for syphilis in such subjects. If the findings of earlier workers could be reproduced and confirmed the results obtained would be expected to contribute much to our fundamental knowledge of syphilis and to the practical control of treponemal infections. Material and methods EXPERIMENTAL SYPHILIS IN RABBITS A total of 37 young adult male rabbits had been inoculated intratesticularly with Nichols virulent strain of T. pallidum 2 weeks to 52 months previously. In 36 rabbits bilateral orchitis developed in an average incubation period of 10 days and their sera became reactive to both the VDRL and TPI tests. Results of serial testing with the quantitative VDRL slide test varied from nonreactive to a maximum titre of 1: 128, while the TPI tests were reactive except when cases were tested in the earliest stages of infection. The TPI tests were performed by the technique as modified by Metzger and Ruczkowska (1962) and the VDRL tests according to the procedure in the Manual of Serologic Tests for Syphilis (1964). All 36 successfully infected rabbits were seroreactive to the VDRL and TPI tests when the experiments were