precipitins 235 



Haptens Yield Precipitates With Homologous Immune Serum. 

 — Antibodies are not produced when the hapten fraction alone is 

 injected but are produced as a rule when the hapten-protein 

 complex is used for immunization. For example, Type II pneumo- 

 coccus immune serum will agglutinate Type II pneumococci, form 

 a specific precipitate when mixed with a solution of Type II pneu- 

 mococci or when mixed with a protein-free solution of Type II, 

 type specific polysaccharide. As previously mentioned in this 

 chapter, Heidelberger and Kendall have used the quantitative 

 precipitin test to determine the amount of type specific polysac- 

 charide present in a solution as well as in the standardization of 

 antisera. 



Reasons for Diluting Immune Serum in Agglutinin and Anti- 

 gen IN the Older Precipitation Tests. — It will be observed from 

 the descriptions given in this chapter of various older methods of 

 performing the precipitin test and of using it for quantitative 

 estimations of antigen or antibody that invariably the latter is used 

 in relatively low dilutions, while tlie antigen is highly diluted. 

 This may seem strange since in previous chapters, where examples 

 of bacterial agglutination are given, it is stated that the suspension 

 of bacteria is kept constant and various dilutions of immune serum 

 are used to ascertain the greatest dilution (titer) giving agglutina- 

 tion. 



Zinsser (1930, 1931) gives an excellent discussion of these ap- 

 parently contradictory procedures and offers an explanation that is 

 held by a large number of immunologists. In the first place it is 

 quite generally believed that serological tests involving agglutina- 

 tion, precipitation or flocculation are essentially alike so far as the 

 mechanisms involved are concerned. While the underlying mecha- 

 nisms are discussed in the chapters on colloids, agglutination, 

 complement fiLxation, and flocculation, it would seem desirable 

 to sketch briefly a few commonly held concepts. When bacterial 

 immune serum is added to an homologous suspension of bacteria, 

 it is thought that bacterial cells become to some extent filmed 

 with antibody-globulin and that agglutination results from certain 

 changes in membrane potentials and in cohesive forces, electrolytes 

 being necessary for the reaction. It is found quite practicable to 

 use high dilutions of the immune serum and yet have enough serum 

 globulin per cubic centimeter to film the bacteria. It is thought 



