Effect of crystalline penicillin and bicillin-1 on experimental syphilis in the rabbit. Electron microscope study.

In continuing the study of the mode of action of penicillin, it was decided to compare the therapeutic effect of single massive doses of crystalline penicillin andof bicillin-1 (benzathine penicillin, which produces therapeutic serum levels for 2 to 4 weeks). Evaluation of the effectiveness of these two preparations was based on clinical observation of the resorption of the chancres, the disappearance of the treponemes, the transfer of tissue from the lesions in the treated rabbits to healthy rabbits, and serial serological tests. At the same time, the authors carried out electron microscope examinations of fragments of chancre tissue with a view to studying the fine processes of interaction between the chancre cells and the treponemes. The study showed, that, despite the high concentrations of penicillin in the serum after one injection of crystalline penicillin, the rabbits were not cured, whereas after administration of bicillin cure was achieved in the majority of the animals. This experiment confirmed that a prolonged concentration of penicillin is essential for therapeutic effectiveness. At the same time it showed that treponemes become more subject to phagocytosis by the cells and to subsequent digestion, mainly by macrophages. In lymphocytes, endothelial cells, and plasmocytes, endocytobiosis apparently takes place. Consequently, in penicillin therapy of syphilis, a therapeutic effect is obtained by the combined action on the treponemes of the antibiotic and the macro-organism. Despite the great successes achieved in the treatment of syphilis with penicillin, a number of aspects of its mode of action are still obscure. In selecting a preparation for treating syphilis, doctors are guided by various considerations. Some believe that the higher the concentration of penicillin in the blood stream the better, and, on that basis, they administer penicillin every 2 or