Since Bordet and Gengou in 19061 announced the discovery of the etiological cause of whooping cough, basing their claim mainly on the complement fixation reactions given by the serum of whooping cough convalescents, complement fixation has been studied by many serologists both from an etiological and from a diagnostic standpoint.
Bordet and Gengou used as antigen a saline emulsion of a culture of the Bordet-Gengou bacillus on solid medium. Four hours at room temperature were allowed for fixation, and readings were made the following day. In later publications2 the constancy of a positive complement fixation reaction among convalescents is reaffirmed, but no figures are given. The work of Bordet and Gengou has been confirmed more or less completely by some investigators and by others their claim has been declared invalid. Meier3 found the serum of pertussis patients to react with an extract of the lung tissue of