Syphilitic rabbits inoculated intratesticularly and treated with arsphenamine before the 69th day of the disease, when reinoculated with the same strain of treponemata and in a manner identical with that of the first inoculation) are capable of responding to the infection in at least five different ways. In addition to exhibiting a local lesion at the site of reinoculation, accompanied by dissemination of the virus, they may show no local lesion at all but present evidence of dissemination of the virus together with the development of a positive Wassermann reaction. In some instances the virus may be recovered from the reinoculation site although no local lesion is produced there and no dissemination of the virus can be shown to take place. An occasional animal treated before the 69th day of the disease remains completely refractory to a second infection.
When treatment is postponed to 6 months or more after the original inoculation, reinfection carried out by intratesticular injection is almost always impossible and such animals appear to be entirely refractory. However, if rabbits treated late are reinoculated with the homologous strain by depositing the virus upon a granulating wound on the back, successful reinfections can be accomplished in at least 50 per cent of the test animals. The resistance which develops in rabbits in the course of syphilitic infection is, then, not absolute but relative.
It is pointed out that these results cast discredit upon the validity of the reinoculation method as a test of cure in syphilitic infection. It is also suggested upon the basis of these experiments, that the subsequent occurrence of a positive Wassermann reaction in patients with early syphilis in whom the Wassermann reaction has become negative under treatment may not always represent a relapse in the the disease but possibly in some instances a new infection without clinical signs.