In 1942 Enders and Cohen1 of the Department of Bacteriology, Harvard University, described a complement fixation test for mumps. The test employed a suspension of parotid glands from monkeys infected with mumps virus. The test was found useful in the diagnosis of some unusual manifestations of mumps infection, such as meningoencephalitis in the absence of parotitis.2 Positive complement fixation reactions were obtained with the serums of 42 per cent of persons without previous history of mumps, which was interpreted as a measure of the frequency of inapparent infection with the mumps virus.
Habel,3 Levens4 and others subsequently adapted the mumps virus to the chick embryo, thus furnishing a cheaper and more readily available source of mumps antigen. Subsequently Henle and others5 of the Department of Pediatrics, University of Pennsylvania, showed that the chick embryo antigen consists of a mixture of two serologically distinct complement fixation