380 BIOLOGY OF PNEUMOCOCCUS 



Complement-Fixing Antibodies 



The reaction of complement fixation is so far inferior in deli- 

 cacy to that of agglutination, precipitation, or mouse protection 

 for the serological diagnosis of pneumococcal types that the sub- 

 ject can be dismissed with brief mention. Hanes (1914), 588 using 

 the method, found that strains of Pneumococcus mucosus were 

 more closely related to Pneumococcus than to Streptococcus. 

 There was a certain amount of cross-fixation between immune 

 serum of Types I and II, and Type III antigens, whereas anti- 

 streptococcic serums deviated complement only in the presence of 

 antigens made from homologous strains. Christensen (1922) 2289 

 employed the method of complement fixation to check type-deter- 

 mination of pneumococci of the first four types made by the ag- 

 glutination reaction but, because the first-named method was more 

 complicated and required a longer time for its execution, Chris- 

 tensen did not recommend its use in place of agglutination. In the 

 studies made by Avery and Heidelberger (1925) 49 on the anti- 

 bodies demonstrable in the serum of rabbits immunized by injec- 

 tion of intact pneumococci and of their carbohydrate and protein 

 derivatives, the method of complement fixation yielded results 

 agreeing with those obtained by specific precipitation. Bull and 

 McKee (1929) 180 applied the method to test the production of 

 antibodies in rabbits immunized with heat-killed broth cultures of 

 pneumococci. Serum from animals immunized with a Type II 

 strain fixed complement in the presence of antigens of Types I, II, 

 and III, but the titer was always higher with the homologous 

 antigen. The same observation held true for Type III antiserum. 

 From rabbits injected with a Type (Group) IV organism, the 

 serum was potent when the homologous organism was used as anti- 

 gen and only slightly weaker in the presence of Type I antigen. Al- 

 though the serums were low in agglutinin titer, their action was 

 type-specific. 



The mechanism of the complement-fixation reaction with the 

 components of Pneumococcus, and the disparity between the abil- 



