114- BIOLOGY OF PNEUMOCOCCUS 



strains differing from the others, which at that time could not be 

 further subdivided. These ten groups were designated as Types IV 

 to and including XIII. 



Finding that therapeutic antiserums for Types I, II, and III 

 had little protective power against Types IV to XIII, the authors 

 prepared from rabbits monovalent antiserums of high agglutina- 

 tive and protective titer for each type. The Cooper Type IV in- 

 cluded an "Antitoxin" strain from the Lilly Laboratories, Robin- 

 son's Group IVB strain, and one that corresponded to Griffith's 

 10. These strains were highly virulent for mice, and of the nine- 

 teen human cases of lobar pneumonia from which pneumococci 

 were isolated, sixteen were rated as severe. Type V included 

 Avery's HA and Robinson's IVE strains. All showed a tendency to 

 hemolyze red cells in blood broth, and had a high initial virulence 

 for mice, which however was rapidly lost. Type VI strains were 

 usually less virulent for mice and their hemolytic action less 

 marked than that of Type V, but more pronounced than that of 

 the majority of other strains. Type VI corresponded to the largest 

 group separated by Griffith from Group IV and found by him to be 

 second in prevalence to Types I and II. The Type VI strains had 

 such a low virulence for mice that they were not suitable for pro- 

 tection tests, nor could their virulence be sufficiently increased for 

 this purpose. Type VIII included Robinson's Group IVA organism 

 and the atypical Type III strain described by Sugg and his asso- 

 ciates. These strains agglutinated with Type III serum to such a 

 marked degree that they might easily have been identified as be- 

 longing to this original type. All Type IX cultures showed low 

 virulence for mice. The Type X strains possessed slight or mod- 

 erate virulence. The four strains designated as Type XI exhibited 

 moderate hemolytic action and were of average to high virulence 

 for mice, which however was quickly lost. The Type XII strains 

 were moderately virulent for mice. The virulence of the Type XIII 

 strains was similar to that of Type XL 



In 1932, Cooper, with the collaborators Rosenstein, Walter, and 



