Superinoculation experiments with Treponema pallidum

The majority of investigators have interpreted the results of superinoculation experiments with Treponema pallidumas showing that one infection affords protection against another. The chief criterion for determining results has been the production of a characteristic lesion containing spirochetes, it being virtually assumed that if no lesion occurred no infection had taken place. When it is recalled that the lesion produced at the portal of entry in a first infection may be very slight or entirely absent1and that organisms may multiply in the body for months or even years without giving rise to any external manifestation of disease, it is obvious that such a standard of measurement is of more value as an index of the ability to produce a manifestation of disease than of infection, and that infection cannot be excluded upon this basis. It would appear, therefore, that before the results of superinoculation experiments can be made clear, the subject must be approached from a broader point of view and that evidence must be adduced which will enable one to see beyond the reaction at the site of inoculation.With this idea in view, a large series of superinoculation experiments was carried out on rabbits with five strains of Treponema pallidurnrepresenting organisms of a wide range of virulence for these animals. These strains included the highly virulent ones of Nichols and of Zinsser and Hopkins, isolated in 1912 and 1913, and three less virulent strains, isolated during the fall of 1919. In general, the animals were first inoculated in one or both testicles while the second inoculation was made intracutaneously on the sheath or at the base of one ear using equivalent doses of a testicular emulsion.