and the sensitized cells combined with all of the complement, 

 leaving- none to act on the sensitized rabbit red cells when they 

 were added. In Tube B complete hemolysis occurred since the 

 normal serum could not sensitize the bacteria in the pestis emulsion 

 and hence the complement remained free to act on the sensitized 

 red cells when they were added. Tubes C and D are additional 

 controls. They showed complete hemolysis since in the former 

 there was no antigen (pestis emulsion) to be sensitized, while in 

 the latter there was neither antigen nor immune serum, since 

 normal serum had been substituted. No hemolysis occurred in 

 Tubes E and F since neither contained complement. Similar re- 

 sults were obtained using an emulsion of typhoid bacilli and anti- 

 typhoid immune serum in place of tlie pestis emulsion and its 

 corresponding antiserum. 



These authors also found tluit fresh human serum could be 

 u.sed as a substitute for guinea pig complement. 



Application' of Complkmp:nt Fixation. — It is obvious that this 

 technique could l)e used either to identify an unknown organism 

 or to ascertain whether antibodies for known organisms were 

 present in the blood of patients. As an illustration of this latter 

 possibility, Bordet and Gengou showed that an emulsion of 

 H. pertussis when mixed with serum from whooping cough cases 

 becomes sensitized, as shown by their capacity to fix complement. 



At the present time bacterial complement fixation is used largely 

 as an aid in the diagnosis of obscure gonococcal infections in the 

 human being and for the detection of P. maUei infection in the 



