582 BIOLOGY OF PNEUMOCOCCUS 



Agglutination. Agglutination tests have been utilized in the past 

 for measuring the antibody content of antipneumococcic serum. In 

 view of the more recent work on the subject (Heidelberger and 

 Kabat, 1934 614 ), it appears that agglutination tests may give a 

 definite measure of the antibody response of animals but owing to 

 uncontrollable variables the usual method does not yield sufficiently 

 consistent results to justify its use as a routine means of stand- 

 ardizing serums. 



Precipitation. Accumulated evidence strongly indicates that the 

 effective therapeutic antibody in antipneumococcic serum is closely 

 related to, if not identical with, the immune substance reacting 

 with the type-specific capsular polysaccharide. The logical course 

 in establishing in vitro methods of standardization is, therefore, to 

 utilize tests employing the specific carbohydrate of the various 

 pneumococcal types as precipitinogen. Although precipitin reac- 

 tions between antipneumococcic serums and corresponding anti- 

 gens were observed soon after the development of immune serum 

 (Panichi, 1907 1046 ), it was not until Heidelberger and Avery 606 iso- 

 lated the capsular polysaccharide that efforts were made to apply 

 specific precipitation methods in the standardization of antipneu- 

 mococcic serum. With many of the tests carried out with polysac- 

 charides similar to the original preparations of Heidelberger and 

 Avery, the results have been decidedly promising. It is probable, 

 however, that even more accurate and reproducible titrations may 

 be obtained with the acetyl form of polysaccharide more recently 

 described by Avery and Goebel (1933), 46 or better still, with the 

 purified materials prepared according to the later methods of Hei- 

 delberger, Kendall and Scherp. 627 



In general, there have been three methods employed for deter- 

 mining the precipitin content of antipneumococcic serum: one 

 using a constant amount of polysaccharide mixed with varying di- 

 lutions of serum ; another utilizing the principle of optimal pro- 

 portions of antigen and antibody; and, finally, one dependent 



