(medicine), a method of diagnosing syphilis by means of a serological reaction. Named after A. von Wassermann. The Wassermann test is based on the ability of blood serum of syphilitic patients to form a complex with the appropriate antigen that absorbs complement (a component of normal serum); erythrocytes of sheep’s blood serve as the antigen, and the antibody is human blood serum. If there is no dissolution of the erythrocytes (hemolysis) when a hemolytic serum is added, the Wassermann test is considered positive (syphilis is present); if hemolysis is present, the test is negative (syphilis is absent). The Wassermann test makes possible the detection of syphilis in the absence of clinical symptoms; it also serves as a criterion of effectiveness of treatment. The Wassermann test is compulsory for pregnant women for prophylaxis of congenital syphilis in infants, for blood donors, and others. The test is conducted before a patient is cleared from the syphilis rolls and when he is issued a marriage license. Positive Wassermann reactions may also be observed in several diseases not of syphilitic origin (for example, leprosy, malaria, typhus, relapsing fever, typhoid fever, smallpox, scarlet fever, influenza, measles, brucellosis, viral pneumonia, and infectious mononucleosis), as well as in certain physiological states (during menstruation; in 2 percent of women during the second half of pregnancy), and when taking certain medications internally (false positive reactions). Therefore, repeated testing is necessary in case of doubt.