RESUMO
In our experiments certain acid-fast bacteria, wheter in alcoholic or salt-solution suspensions of the entire bacterial mass, gave the complement fixation only with lepers' sera, not with control sera. Our best antigen of this type was made from the Bg strain obtained from leprous blood, but the percentage of positive results with it was not as high as with other types of antigen. A similar antigen made from the human tubercle bacillus often gave positive reactions with lepers' sera, but not in a high percentage. One of a rat leprosy bacillus culture gave no positive reactions. An antigen of the Bg strain made by extracting the ether-soluble elements and adding a little cholesterin gave a much higher percentage of positive reactions with lepers' sera. However, the sensitiveness of this type of antigen is not limited to those made with the organisms from leprosy; those from other acid-fast bacteria give fairly many positive reactions, though there was more or less disparity among them as regards percentages. With control sera these antigens gave few positive reactions. Though the Bg antigen of this type is the best, those made similarly from the Cd strain, the human tubercle bacillus, the timathy hay bacillus, and one isolated fron running water have nearly the same value. Those of the rat leprosy bacillus used, and of the avian tubercle and smegma bacilli, are of less value. Though the antigens named have a strong specific capacity for fixation with lepers' sera, it is on the other hand impossible to distinguish between the various kinds of bacilli by means of lepers' sera.