1. The intravenous administration of six doses of arsphenamine to syphilitic rabbits in amounts of 10 mg. per kilo, 127 days after inoculation is sufficient to render the popliteal nodes of such animals incapable of transmitting the infection to normal animals.
2. Syphilitic rabbits that have been treated in this manner and whose popliteal nodes 32 to 38 days after treatment have been shown to be incapable of transmitting the infection to normal animals are, as far as can be judged by the absence of a local lesion, refractory to a second inoculation of active virus of the same strain, if the inoculation be made intradermally at the base of the ear and carried out 209 days after the first inoculation.
3. Untreated syphilitic rabbits are also refractory toward a second inoculation made in a similar manner and at a similar interval following the first inoculation.
4. Evidence is offered in favor of the view that the most satisfactory method of evaluation of antisyphilitic agents in experimental syphilis of the rabbit is that of lymph node transfer.
5. Evidence is offered in support of the view that the state of refractoriness toward a second inoculation exhibited by syphilitic rabbits may be explainable upon the basis of either an acquired immunity or persistence of a focus of living treponemata in the body.