Although antibodies can be produced by the immunization of animals with cultivated Treponema pallidum, and although these antibodies exert specific agglutinative and treponemicidal action upon the culture organisms, they possess, at least in the concentration so far obtained by us in rabbits and sheep, practically no action for virulent treponemata obtained directly from lesions. There seems to be in the infected body an inability to exert a purely serum action upon the virulent treponemata, a condition of affairs which may well lead to a lack of antigen absorption on the part of the body and a consequent failure to produce serum antibodies.
We do not think that this should in any way discourage our further investigation of the protective action of antibodies produced with culture pallida. On the one hand, the slight occasional agglutination and the lower proportion of takes with the concentrated serum in the last experiment at least indicate the possibility that we have been working with sera that are not sufficiently powerful and that just as with work with the pneumococcus and other highly invasive organisms, a serum of considerable antibody contents must be used before results can be expected. Again, the destruction of treponemata and the healing of lesions which undoubtedly takes place in rabbits, sometimes with surprising speed, may be a cellular destruction, and by injecting the sera either locally or intravenously and giving them time to be absorbed by the cells before injecting virulent material, better results may be obtained. This direction of research as well as further studies on the antagonistic cellular processes against the pallida, the immunization of animals with killed virulent organisms, and the antibodies in rabbits and human beings during the course of infection and after recovery are being investigated, and we hope to be able to report upon them in the near future.