Syphilitic rabbits can be treated with arsphenamine in such a manner as to render the lymph nodes incapable of transmitting the infection to normal rabbits. This can be accomplished if treatment is begun either early or comparatively late in the course of the disease. If treatment is begun early, the animals are almost uniformly susceptible to a second infection, whereas, if it is begun late, they are almost uniformly refractory to a second infection. It is suggested that this refractory state in rabbits may be explained by the existence of an acquired immunity which persists after the abolition of the disease, rather than to the persistence of the first infection.
It would appear that it is possible under certain conditions to reinoculate rabbits and produce generalized infection without producing any lesion at the portal of entry.