208 BIOLOGY OF PNEUMOCOCCUS 



sidered by the authors as a prerequisite, but not the sole factor, 

 in determining the virulence of an organism for rabbits. Continu- 

 ing the investigation, Shaffer with Enders and Wu 1259 studied 

 two smooth strains of the same organism, one virulent and the 

 other relatively avirulent for rabbits. Although no antigenic differ- 

 ences between the two organisms were revealed by cross-absorp- 

 tion of agglutinins from homologous antiserum, the latter strain 

 lost its capsule in dextrose serum-broth cultures about eight hours 

 earlier than was the case with the rabbit-virulent organism. With 

 the loss of capsule there was marked shrinkage in volume, altera- 

 tion in the zone of acid agglutination, susceptibility to agglutina- 

 tion in antirough pneumococcic serum and to phagocytosis. 



The results which followed the intravenous injection into rabbits 

 of the two strains varied with the state of the capsule. A culture 

 of either strain became susceptible to the blood-clearing mecha- 

 nisms contemporaneously with the onset of capsular degeneration 

 and the beginning of other concomitant changes at the surface of 

 the organism which occurred much earlier with the less virulent 

 strain. Phagocytosis by the leucocytes of the normal animal either 

 in vitro or in vivo was observed only at such a time as the capsule 

 had become impaired. The authors (Enders, Shaffer, and Wu) 361 

 concluded that virulence for rabbits of the two strains of Type III 

 Pneumococcus does not imply that this animal possesses a defen- 

 sive mechanism which is absent in other species, since it was pos- 

 sible to demonstrate similar differences in virulence when the or- 

 ganisms were injected intravenously into mice. Therefore, "the 

 factors determining the degree of virulence of these strains are to 

 be sought in the organisms themselves, rather than in the kind of 

 host." 



In a fourth publication of the series, Enders, Wu, and Shaffer 863 

 discovered that the addition of the C Fraction of Tillett and Fran- 

 cis 1409 to serum-leucocyte mixtures decreased the phagocytosis of 

 both rabbit-virulent and avirulent strains of Type III by the cells 

 and serum of both man and the normal rabbit. Furthermore, the 



