The direct, the modified direct and the indirect
complement-fixation tests were investigated as methods for the detection of
antibodies for the enzootic
pneumonia mycoplasma and for Mycoplasma hyorhinis in the serum of infected pigs and of immunized rabbits. Only the modified direct
complement-fixation test in which the guinea-pig
complement is supplemented with fresh, normal unheated calf serum was suitable for the detection of mycoplasma
antibodies in sera of infected swine. Based on the close correlation between the production of typical lung lesions in experimentally infected pigs and the appearance of significant serum antibody titres, the modified direct
complement-fixation test provides for the first time a sensitive, specific in vitro method for the detection of enzootic
pneumonia in the live pig. This test also permitted the in vitro differentiation of the mycoplasma causing enzootic
pneumonia from M. hyorhinis which causes polyserositis.
Antibodies in the sera of rabbits were demonstrable by the ordinary direct
complement-fixation test. However, in contast to the observation made with swine sera, only a slight quantitative antigenic difference between the enzootic
pneumonia mycoplasma and M. hyorhinis was seen when the tests were performed with rabbit serum antibodiies.