As I have been asked many times by colleagues in Germany and abroad for information concerning the origin of the so-called "Reiter strain" of Treponema pallidum, I should like to give the following details:These investigations were first carried out by M. Ficker at the Kaiser-Wilhelm Institute of Experimental Therapy in Berlin and were continued and completed by myself after Ficker had left the Institute for South America in 1923. Ficker had been able to isolate a number of strains of T. pallidum and I continued his investigations and also succeeded in isolating some strains of T. pallidum from fresh cases of syphilis. The specificity of all these strains has been proved by inoculation of rabbits. There is no doubt that the so-called "Reiter strain" is a genuine Treponema pallidum. Altogether, nine to eleven strains were isolated during that time in the manner described below.By these experiments some strains were found to behave differently when inoculated into rabbit testes. A second superinfection would "take" after a rather short interval and produce either orchitis or only some small nodules in the testicles which could hardly be discovered. Sometimes a second infection would not "take" at all. Several experiments were performed with the strain B.36, but unfortunately to-day I am not able to say definitely which strain I sent to Mulzer in 1927, because all protocols have been lost! I should like to emphasize strongly the proved virulence of this so-called Reiter strain, quoting the following paragraph verbatim: "We inoculated one ml. of a pure fluid culture which was kindly provided by Prof. Reiter and which had been subcultured about 200 times in the usual manner into each testis of two rabbits. As the living, somewhat coarselooking spirochaetes were rather poorly motile, we fully expected that these pallidum-like culture spirochaetes would have lost their pathogenicity for rabbits. On the contrary, after an incubation period which lasted about 50 days, both rabbits developed a bilateral orchitis containing numerous typical and extraordinarily motile spirochaetes. We have also