ANTIBODIES TO PNEUMOCOCCUS 389 



forces which accounted for the resistance of normal and immunized 

 animals to Pneumococcus. One school contended that immunity 

 was due to bactericidins ; the other maintained that the immunity 

 was antitoxic in nature. The idea that mobile cellular elements — 

 the leucocytes — might intervene in arresting pneumococcal infec- 

 tion came as an innovation and at first was not readily accepted. 

 For example, Bonome 137 shared the conception that the blood of 

 immunized animals acquired increased bactericidal power for 

 pneumococci and although he observed both leucocytosis and 

 phagocytosis, he did not perceive that the phenomena could be 

 the. basis of bactericidal action. It was Issaeff (1893) 673 who, as 

 a result of his experiments, abandoned the idea that antitoxin was 

 a factor, and emphasized the fact that phagocytosis played a most 

 important part in acquired immunity to Pneumococcus. Mennes 

 (1897) 893 was unable to demonstrate any effect of the white cells 

 of normal blood on the development of pneumococcal infection. 

 According to his views, the primary defensive element was the 

 serum and not the leucocytes. The white cells of immune rabbits, 

 however, exerted marked phagocytic action, and Mennes concluded 

 that the immunity of the rabbit to pneumococcal invasion de- 

 veloped from a modification of the serum, and that tiie modifica- 

 tion activated the phagocytic property of the leucocytes. 



In 1904, Neufeld and Rimpau 997 definitely discarded bacteri- 

 cidins and bacteriolysins as forces operating in antipneumococcic 

 immunity and reported that the addition of specific immune serum 

 to normal rabbit leucocytes imparted to the cells vigorous phago- 

 cytic ability. The authors then extended the experiments to include 

 the in vivo action of immune serum on virulent cultures injected 

 into mice. When the culture alone was injected intraperitoneally, 

 the organisms multiplied and only a few leucocytes were seen to 

 contain cocci, but when both culture and serum were injected, a 

 large number of pneumococci were engulfed by the white blood 

 cells. By absorption experiments, Neufeld and Rimpau demon- 

 strated that the serum acted on the cocci, whether living or killed, 



