ANTIBODIES TO' PNEUMOCOCCUS 381 



ity of specific antipneumococcic serums produced respectively in 

 the rabbit and horse to bind complement in the presence of homolo- 

 gous antigen, have been studied by Goodner and Horsfall. 538 With- 

 out retailing the experimental details, it may suffice to abstract 

 the discussion and summary. The experiments reported supported 

 the view that the failure to obtain complement fixation with com- 

 binations of pneumococcal capsular polysaccharide and specific 

 immune horse serum is not due to some heterologous inhibitor in 

 immune horse serum but is to be referred rather to some property 

 of the horse antibody itself or some property of the immune ag- 

 gregate resulting from the union of this antibody and the poly- 

 saccharide. This property is lacking in the specific antibody in 

 immune rabbit serum which, in the presence of homologous poly- 

 saccharide, is capable under proper conditions of binding com- 

 plement. Furthermore, the results support the view that the fixa- 

 tion of complement is a phenomenon of selective absorption. That 

 one type of aggregate absorbs complement while another fails to 

 do so is curious, but far from unique. Goodner and Horsfall found 

 a close parallelism in the fact that horse antibody-polysaccharide 

 aggregates absorb cephalin, while aggregates containing rabbit 

 antibody selectively absorb lecithin. 



The essential role of serum lipids in the demonstration of the 

 phenomena of specific precipitation and agglutination has been 

 described by Horsfall and Goodner. 657 The removal of lecithin 

 from antipneumococcic horse serum and, to a lesser degree, the ex- 

 traction of cephalin from antipneumococcic rabbit serum cause a 

 loss of the visible phenomena of agglutination and precipitation. 

 It was found that initial activity of type-specific antibody can be 

 restored to extracted immune horse serum by the addition of leci- 

 thin, and to extracted rabbit serum by the addition of cephalin. It 

 is therefore probable that the content of these two phospho-lipids* 

 in the serum of the two animal species may, in part, account for 



* In a recent brief communication, Horsfall, Goodner, and MacLeod659 de- 

 scribe the antibody in pneumococcal immune horse serum as a lecithoprotein 

 and that in immune rabbit serum as a cephaloprotein. 



