202 BIOLOGY OF PNEUMOCOCCUS 



of the virulence of the strain, but the evidence presented is too 

 meager to be convincing. 



SUBSTANCES THAT ENHANCE VIRULENCE 



In Chapter III mention was made of substances or preparations 

 which possessed the ability to increase the invasive power of pneu- 

 mococci. The virulin of Pittman and Falk, 1092 the extracts of Pitt- 

 man and Southwick, 1093 the leucocidin of Oram, 1032 and the toxic 

 autolysate of Parker and Pappenheimer 1063 are examples of sub- 

 stances which to a greater or less degree possess this property. A 

 similar action was observed by Sia, 1266 who found that the addi- 

 tion of a very small amount of soluble specific substance or of 

 young broth cultures of pneumococci to avirulent cultures of 

 homologous type when mixed with rabbit or cat serum-leucocyte 

 mixtures favored the growth of the organism. The authors inter- 

 preted the result as indicating that soluble specific substance had 

 the power of rendering virulent an avirulent Pneumococcus of the 

 same serological type. Sia and Zia 1275 reported that the injection 

 of Type II soluble specific substance into rabbits depressed the 

 resistance to such an extent that the animals succumbed to the 

 intravenous injection of an otherwise sublethal dose of pneumo- 

 cocci of the same serological type. The authors left undecided the 

 question whether the result was to be ascribed to a heightened 

 susceptibility of the animal or to an enhanced virulence of the or- 

 ganism. 



A somewhat similar effect was obtained by Nungester, Wolf, and 

 Jourdonais, 1020 who added gastric mucin to twenty-four-hour 

 broth cultures of Type II pneumococci and injected the mixture 

 intraperitoneally into mice. Control mice received similar injec- 

 tions of the culture suspended in saline instead of mucin solution. 

 At only one dose level was any marked difference noted in the per- 

 centage of survivals among the test and the control animals. The 

 effect was not apparent when the injections were made intra- 

 venously or subcutaneously. Any action of mucin, in spite of its 



