Two experiments are reported in which an attempt was made to determine the extent to which a primary syphilitic infection of the cornea in rabbits is followed by the development of a local corneal immunity, by the generalization of the virus, and by the development of a general immunity to the infection. Female rabbits were inoculated intracorneally with a virulent strain of T. pallidum and the disease was allowed to run its course until the lesions which had developed at the site of inoculation had healed spontaneously. Popliteal lymph nodes were transferred from about one-half of these animals (in the second experiment only) to normal male rabbits and in almost every instance the nodes were proved by this method to contain virulent treponemes, showing that generalization of the syphilitic infection is the rule after intracorneal inoculation. All animals were treated with arsphenamine after the local lesion had subsided (160 and 275 days after the original inoculation). The rabbits were then reinoculated with the homologous strain of treponemes, injections being made into the cornea originally inoculated and also into the skin of the back. In one experiment both corneas were reinoculated.
The incidence of lesions developing in either cornea after reinoculation was higher than the incidence of lesions developing in the skin. The lesions developing in the corneas of the "immune" animals had a longer incubation period and were of shorter duration on the average than the lesions in the control group. As far as intensity of reaction was concerned no difference was observed.
Inoculation of the cornea of rabbits with syphilitic virus is often followed by the development of immunity to the homologous strain of organisms. This immunity is imparted to the skin to a greater extent than to either the cornea inoculated originally or to the opposite uninoculated cornea. It persists after treatment with arsphenamine. It appears to be more marked the longer treatment is postponed.
It is apparent from Table IV that in one-half of all the test animals both cornea and skin were immune to a second inoculation of homologous syphilitic virus. In addition to these there were 5 animals in which the cornea was immune and the skin nearly so, for the lesions which developed in the skin of these animals were minimal in extent and duration and were in no way comparable to those which were observed in the controls. Thus in two-thirds of our animals there developed in both the skin and the cornea, after a primary intracorneal inoculation, a high degree of resistance toward a second inoculation with homologous syphilitic virus, but syphilitic disease of the cornea does not always impart to the cornea itself an absolute immunity to reinoculated homologous virus.