33 



species. The almost complete absence of any evidence of inter- 

 relationship by the ordinary agglutination test is so much the 

 more remarkable. It is true, as mentioned earlier, that the 

 American observers find that certain of the types in Group IV 

 are related to Type II, but, since this relationship can only be 

 demonstrated by using equal parts of serum and suspension, 

 its importance is doubtful. Again, as mentioned on page 22, 

 when highly agglutinable suspensions of cocci in salt solution 

 are used, there is often a precipitation in the form of fine clumps 

 by low dilutions of heterologous sera. This does not occur when 

 the suspensions consist of whole broth cultures of pneumococci. 



The 12 type strains, which have been identified in Group IV, 

 have been repeatedly tested against sera prepared from seven 

 of their number and from the American strains I, II, III, IIa 

 and IIb, equal parts of 1 in 10 serum and broth culture being 

 used. Excepting in the case of *Pn. 26 and Pn. 42, where each 

 of the two strains gave slight agglutination on a few occasions 

 with the heterologous serum, there was a complete absence of 

 any cross-agglutination ; each strain reacted only with the 

 homologous serum. 



The results obtained with whole broth cultures have been 

 confirmed by tests with the peritoneal washings from mice 

 infected with the 12 types of Group IV. The agglutination 

 tests, therefore, establish the serological independence of these 

 Group IV strains from each other and from the three chief types. 



Protection Tests with Group IV Pneumococci. 



Experiments have been made to ascertain whether a pre-, 

 liminary inoculation of any of the three antipneumococcal sera 

 of Types I, II or III confers protection on mice against a sub- 

 sequent inoculation of a Group IV strain. The first two sera 

 were protective against the homologous cultures (Type I and 

 Type II), which were of high virulence ; the Type III serum 

 protected mice against Type III, but the strain used was not 

 of maximum virulence. None of the three sera conferred 

 appreciable protection on mice against any of the Group IV 

 strains which were tested; even where the test strains were of 

 moderate and irregular virulence, the mice died of pneumococcal 

 septicaemia after some delay. 



It has not been possible to attempt, in the case of the 

 majority of the Group IV strains, an exact estimation of the 

 presence of minor degrees of protective power in their sera 

 against other members of the group, on account of their irregular 



* An absorption of agglutinin test, made with Pn. 42 and Pn. 26 

 strains and sera, showed that the homologous strains removed the agglu- 

 tinin, and the heterologous strains had no effect. In no other instance 

 was the absorption of agglutinin test found to be necessary. 



x 17680 B 



