Test for syphilis, serum from positive cases flocculating when mixed with a lecithin-type ‘antigen’ extracted from normal beef heart muscle. Varying proportions of patient’s serum and saline- activated antigen are mixed, vigorously shaken, and diluted with further saline. A uniform opalescence is indicative of a negative reaction; flocculation indicates positivity. Some other infections (particularly leprosy and yaws) may give similar reactions. In the Kahn verification test the entire test is conducted at room temperature, at 37°C and at 2°C, syphilitic reactions gaining in strength as the reaction temperature rises.