206 BIOLOGY OF PNEUMOCOCCUS 



erate, or low intraperitoneal virulence. Type III strains were of 

 relatively high intranasal and intraperitoneal infectivity ; Type II 

 organisms were low in intranasal but high or moderate in intra- 

 peritoneal virulence ; Type I strains were all low in intranasal but 

 either high or moderate in intraperitoneal virulence ; while the ma- 

 jority of strains of other types were low both in intranasal and 

 intraperitoneal pathogenicity. Intranasal virulence of pneumo- 

 cocci was not enhanced by animal passage, but nasal passage re- 

 duced the intranasal virulence to zero without altering intraperi- 

 toneal virulence, colony form, or agglutinative specificity of the 

 strains. Passage by the intraperitoneal method maintained the 

 characteristic level of intranasal virulence for a period, increased 

 intraperitoneal virulence in some instances, but did not affect 

 colony form or agglutinative properties. 



VIRULENCE IN RESPECT TO ANIMAL SPECIES 



In addition to individual differences in pneumococci, variations 

 in the susceptibility of various animals are factors to be reckoned 

 with in the evaluation of the virulence of a given type or strain. 

 An organism may possess superior virulence for animals of one 

 species and yet fail to infect those of another species, although the 

 animals may readily be infected with representatives of a different 

 variety or type. Eyre and Washbourn, 374 in 1898, reported that, 

 after increasing the virulence of a culture for guinea pigs by re- 

 peated passage through a series of these animals, there was no 

 change in the virulence of the organism for mice. Fourteen years 

 later, Neufeld and Ungermann 1001 " 2 observed that while repeated 

 passage of a strain of Pneumococcus through the guinea pig ele- 

 vated the virulence of the organism for animals of the same spe- 

 cies, similar serial propagation in mice failed to increase the in- 

 fectiousness of the strain for the guinea pig. 



In 1912, Truche and Cotoni 1423 reported that strains of pneumo- 

 cocci isolated from human sources were rarely virulent for rabbits 

 or guinea pigs. Strains virulent for rabbits were always infective 



