110 BIOLOGY OF PNEUMOCOCCUS 



isms of the fixed types. The acid-agglutination of the majority of 

 pneumococci of Types I and II was extremely susceptible to the 

 inhibiting action of salts, but this was not true of other pneumo- 

 cocci. These influences, with the variations they cause, while of a 

 certain philosophic interest, have little bearing on the practical 

 application of agglutination to the classification of members of 

 this bacterial species. 



Following the lead developed by Avery, Stillman 1327 further sub- 

 divided Type II strains into twelve distinct groups. These were 

 designated as Ila to Ilm. Groups Ilb-c-f-m originated in human 

 mouths. Groups Ila and Ilh were encountered largely in connec- 

 tion with disease, while the general fatality of acute lobar pneu- 

 monia due to these atypical Type II pneumococci was fairly high. 

 Stillman's tables, showing the percentage of incidence and of 

 mortality of strains of these subgroups, offer an interesting com- 

 parison with those given later by Cooper and her associates. They 

 serve to emphasize the close relation which exists between some 

 members of the Type II and those of the new types formerly in- 

 cluded in Group IV. 



In conformity with Stillman's and Olmstead's investigations, 

 Christensen proved that Type IVm of Stillman also constituted a 

 heterogeneous group which could be further divided into subordi- 

 nate groups. Christensen 228 " 9 carried out comparative tests by 

 means of agglutination, agglutinin-absorption, and complement 

 fixation and gave preference to the simple agglutination technique 

 as being the most convenient and efficient method for serological 

 differentiation. 



The splitting of Type II into separate groups was apparently 

 unknown to Hintze, 646 who found anomalies in the American Type 

 II and was not convinced that it was a clear-cut group. He, among 

 others, also classified Streptococcus mucosus as Type III Pneumo- 

 coccus, although strains of this organism were encountered that 

 gave atypical reactions. 



Yu, 1567 studying fifty-one strains by the agglutination method, 



