The therapeutic value of arsphenamine was established by Ehrlich and Hata1 as a result of experiments on various animals (mice, rats, chickens and rabbits) inoculated with syphilis, trypanosomiasis, chicken spirillosis and recurrent fever. The nature of these diseases is such as to permit of a more or less direct observation of the effect of the drug on the causative agent. Recurrent fever and chicken spirillosis are both blood infections, and systematic examination of the blood affords a fair picture of the effect of the drug on the organisms. As for experimental syphilis, conclusions may be drawn from the disappearance of spirochetes from the chancre and the healing of the lesions.
An unfavorable feature of this test for the spirocheticidal activity of drugs, as originally employed by Ehrlich and Hata, is that animals infected with chicken spirillosis, relapsing fever and, to some extent, with syphilis may recover spontaneously. On this