432 BIOLOGY OF PNEUMOCOCCUS 



In 1929, Sia 1269 presented further evidence in support of the 

 view that humoral defensive elements play an important part in 

 natural immunity to Pneumococcus. Mice were given intraperi- 

 toneal injections of serum from the pig and four hours later ac- 

 tively growing cultures of virulent Type I pneumococci were in- 

 jected into the animals. Control mice were similarly injected with 

 serum from susceptible animals (the rabbit and guinea pig) and 

 then inoculated with the same culture. Normal swine serum pro- 

 tected the mice against ten thousand minimal lethal doses of cul- 

 ture, whereas serum from the susceptible animals afforded no pro- 

 tection to the test animals. Pig serum also protected mice against 

 virulent Type II pneumococci and to a lesser degree against Type 

 III organisms. Moreover, absorption experiments again demon- 

 strated that the protective substance was type-specific. 



Le Guyon (1931) 796 investigated the causes of the different re- 

 actions exhibited by rabbits and guinea pigs to pneumococcal 

 infection. The technique employed consisted in inoculating the 

 animals intraperitoneally with a broth culture of virulent pneu- 

 mococci and in examining peritoneal fluid withdrawn at various 

 intervals after injection. Four hours after inoculation, mice de- 

 veloped a marked cellular reaction. Along with many cocci there 

 were always a large number of macrophages of the clasmatocyte 

 type. There was intense phagocytosis by the polymorphonuclear 

 leucocytes and macrophages, but in spite of the reaction the ani- 

 mals developed septicemia and died within eighteen to twenty 

 hours. In guinea pigs four hours after inoculation, the reaction 

 was feeble. Some polymorphonuclear cells and some free pneumo- 

 cocci were present in the exudate, but there was only occasional 

 evidence of phagocytosis. Sixteen hours later, the number of or- 

 ganisms and polymorphonuclear leucocytes had greatly increased, 

 but lymphocytes and macrophages were rarely seen. The pneu- 

 mococci, some of which were phagocyted, were clustered about 

 the polymorphonuclear cells and appeared to be in a degenerated 

 condition. Le Guyon therefore concluded that the initial refrac- 



