The reliability of the blood Wassermann reaction in experimental rabbit syphilis has long been the subject of controversy. Blumenthal and other German workers, using alcohol-soluble antigen and inactivated serum, found that normal rabbits not infrequently reacted positively. By modifying the quantities of antigen and serum used, Blumenthal1 obtained uniformly negative results with nonsyphilitic rabbits but inconsistent results with syphilitic animals. Halberstaedter2 reported negative results in normal rabbits with alcoholic-extract antigen and active serum, but Uhlenhuth and Mulzer3 failed to confirm his findings. On the other hand, Nichols,4 using alcohol-soluble antigen and inactivated serum, found normal rabbits negative and syphilitic rabbits positive. Kolmer and Casselman5 showed an increased tendency to positive reactions in normal rabbits as larger amounts of inactivated serum were used. Emanuel6 and Epstein and Pribram7 stated that the positive blood Wassermann reaction of normal rabbits could be negated temporarily by