ANTIBODIES TO PNEUMOCOCCUS 409 



valent rabbit antiserum prepared with pneumococci of Types II 

 and III also exhibited cross-protection between Type III serum 

 and Type I organisms. Despite the heterologous action observed 

 in the protection test, all the samples of immune rabbit serum 

 tested were found to be type-specific in agglutinin content. 



From the data presented in the communications of Yoshioka 

 and of Kolchin and Gross it is difficult properly to interpret the 

 results. However, against the claims of the occurrence of cross- 

 protection with monovalent immune serum there is a mass of evi- 

 dence attesting the specificity of the reaction when serum is pre- 

 pared from carefully authenticated strains of Pneumococcus and 

 when similarly identified strains are used for testing the protective 

 action of immune serum. The mouse protection test, when prop- 

 erly executed, therefore, remains the final criterion for establish- 

 ing the type-identity of pneumococcal strains. 



RELATION TO OTHER ANTIBODIES 



A definite relation exists between the amount of protective anti- 

 body in a given serum and its content of agglutinins and precipi- 

 tins. Among the many references which might be cited, the work of 

 Heidelberger, Sia, and Kendall (1930) 630 and the study of Felton 

 (1931 ) 407 are chosen as illustrative. The former authors deter- 

 mined a close parallelism between the specifically precipitable pro- 

 tein and the number of mouse-protective units in a wide variety of 

 Type I antipneumococcic serums. So constant were the results 

 yielded by the simple method for determining the amount of pre- 

 cipitable protein in immune serum that the reaction as described 

 in the section of the present chapter dealing with precipitins could 

 be relied upon to measure the protective strength of the serum. 

 Sabin (1931) 1204 was unable to precipitate the totality of protec- 

 tive antibody from antipneumococcic serum by the addition of 

 homologous soluble specific substance and hence assumed the exist- 

 ence of a protective substance distinct from the anticarbohydrate 

 antibody. However, Felton 407 found in samples of Type I anti- 



