Since 1906, the Wassermann complement-fixation test for syphilis has been used by diagnostic laboratories as the most satisfactory indicator for detecting syphilis in the patient's serum. All modifications or new tests have always been compared with the Wassermann reaction, which therefore practically has become a standard. Its limitations, however, are understood and accepted.
In an effort to do away with any test requiring the use of a hemolytic system as a final indicator, direct flocculation methods were elaborated. One of the earliest tests to win recognition was the Sachs-Georgi, which, briefly, consisted of adding the diluted serum of a patient to a saline suspension of heart extract (with and without cholesterin), incubating for two hours at 37 C., and leaving the tubes at room temperature for twenty hours, after which the amount of flocculation in the tubes was read.
In 1921, Dreyer and Ward1 described the Sigma reaction, a