According to the original view of the discoverers the Wassermann reaction was considered, in analogy to the common serological reactions, as being caused by antibodies specific for the infecting microorganisms. This view became doubtful and was abandoned by most authors when it was shown that syphilitic sera react with alcoholic extracts of organs, presumably with lipoids present in these extracts (1-3). The use of extracts of normal instead of syphilitic organs (1) has since been accepted almost generally for the technique of the Wassermann reaction. Several main hypotheses have been advanced in order to explain the formation and properties of the Wassermann reagins. Some authors believed that the action of the syphilitic sera was due not to immune bodies but to non-specific changes of the serum proteins. Others regarded, the reagins as antibodies formed either by autoimmunization with lipoidal substances from the infected organism or with lipoids derived from the spirochetes (cf. Bergel). In the latter case one had to assume that the antibodies produced act not only upon the homologous antigen but also upon lipoids of very different origin.The hypotheses implying an immunization against lipoids met with the difficulty that the attempts to induce the formation of antibodies by injection of lipoids, as a rule, did not yield clear-cut and consistent results. In the positive experiments recorded there was no certainty as to the absence of small quantities of antigenic proteins in the material injected or else the amount of antibody formation was rather insignificant. I 1 Regarding the antigens of blood corpuscles see "On the antigens of red blood corpuscles. The question of lipoid antigens," by K. Landsteiner and J. van der Scheer,