Various modifications of the Wassermann reaction utilizing the complement and natural antisheep hemolysin of human serum, have been advocated from time to time for the purpose of conducting the test in a more economical manner or, more particularly, to increase its delicacy and obviate certain sources of error ascribed to the inactivation or heating of the serum.
Of these methods, that of Hecht (1, 2 and 3) received considerable attention. As originally proposed and with later modification, this test employs an alcoholic extract of guinea-pig heart, human fetal heart and other extracts as antigen using 1 cc. of 1:50, 1:100 and 1:200 dilutions with a constant dose of 0.1 to 0.2 cc. of fresh active serum. The fourth tube of the series serves as the control. After a primary incubation of a half to one hour, 1 cc. of a 2 per cent suspension of sheep cells is added to all tubes followed by re-incubation for one to two hours.