CLASSIFICATION OF PNEUMOCOCCI 117 



agglutination between the two varieties and, with the exception of 

 one strain, that agglutinated with Type XVI immune serum in a 

 dilution of 1 to 32, the two varieties failed to be agglutinated with 

 any of the thirty-two type serums. 



Strains of pneumococci which failed to correspond to any of the 

 thirty-two known types were encountered in China by Wu and 

 Zia, 1552 who reported that among a total of 162 strains tested, four 

 failed to agglutinate with any of the thirty-two type serums. The 

 unclassifiable strains possessed typical cultural characteristics and 

 were virulent for mice. 



It may be expected that other types of pneumococci will in time 

 be added to Cooper's list. There were still a few strains which did 

 not fit into any of the thirty-two groups, and the work of the two 

 Japanese bacteriologists, while leaving doubts as to the soundness 

 of their conclusions, and the results obtained in England, India, 

 and China present the possibility that more heterogeneous strains 

 may be encountered which will be found to form additional sero- 

 logical types. 



There is the further question of the pneumococci causing infec- 

 tions in animals other than man. Grenier (1912) 555 described cul- 

 tures from three sources, namely, guinea pigs, rabbits, and horses. 

 The first two cultures from guinea pigs and rabbits were isolated 

 from animals undergoing experiments with other toxic or infec- 

 tious agents. The pneumococcus infecting the guinea pig was mod- 

 erately virulent for mice and usually led a saprophytic existence in 

 the respiratory and digestive tracts. The culture from infected 

 horses did not originally kill mice but acquired virulence on animal 

 passage. The observations of Grenier suggest that in veterinary 

 bacteriology there may be strains, or even types, which might be 

 found to have interesting pathogenic and serological relationships 

 with pneumococci of human origin. The authors of the present vol- 

 ume disclaim any acquaintance with the literature of that branch 

 of bacteriology, so far as it concerns Pneumococcus, but studies on 



