31 



" atypical " strains occurring in lobar pneumonia in different 

 countries would, I think, be an important contribution to the 

 study of pneumococci from the epidemiological aspect, and for 

 this purpose uniformity of classification, as mentioned above, is 

 essential. I have suggested that these heterogeneous strains 

 might collectively be designated Group IV, each serological 

 type being distinguished by a letter of the alphabet, e.g., 

 Group IVa, &c. The relationship of the " atypical " strains to 

 the three chief types is a subject for future research. Too much 

 emphasis should not, at the present stage, be laid on the atypical 

 Type II strains as having relationship to Type II, but in order 

 to avoid loss of continuity the letters A, B. X might be reserved 

 for those strains of GrOup IV which correspond to the American 

 atypical types, 11a, 11b, IIx. 



Immunological Independence of the Races of 

 Pneumococci. 



In my preliminary note on the incidence of pneumococci in 

 lobar pneumonia, I expressed the opinion that the results of 

 my agglutination tests confirmed the American view, that the 

 three types of pneumococci, I, II and III, were serologically 

 independent. The results of my subsequent work are in 

 accordance with this view. I now consider the evidence based 

 on protection experiments on mice, and, in addition, give the 

 results of agglutination and protection tests with the serological 

 types of Group IV. 



Protection Tests with Types I, II and III. 



In the following experiment evidence of cross-protection was 

 sought between Types I and II strains and sera. The virulence 

 of the strains was such that they killed the control mice in two 

 days after the inoculation of O'OOO 000 1 c.c. of broth culture; 

 the test culture was inoculated 19 hours after the injection of 



