ANTIGENICITY OF PNEUMOCOCCUS 341 



studies on Pneumococcus one finds references to the subcutaneous 

 injection of the organism or its products. The introduction of the 

 intravenous route was followed by the more rapid appearance and 

 a higher level of immunity in the treated animals. The administra- 

 tion of antigens by way of the peritoneal cavity also offered ad- 

 vantages over the subcutaneous route both in time of development 

 of immunity and in heightened resistance. 



In 1922, Bronfenbrenner and Knights 149 published the results of 

 a study on the comparative efficacy of the subcutaneous, intrave- 

 nous, intratracheal, and intrapleural routes for the introduction 

 of pneumococcal antigens. Rabbits were used and the immunity 

 evoked was measured by the bactericidal, opsonizing, and protec- 

 tive power of the serum following the different methods of treat- 

 ment. The bactericidal titer of the serum from rabbits receiving 

 intravenous and subcutaneous injections, as determined by the 

 Heist and Solis-Cohen 634 technique, was approximately the same 

 and was greater than that of the serum of animals injected either 

 by the intrapleural or intratracheal routes. Both the intratra- 

 cheal and intrapleural methods induced a much higher opsonic 

 content of the immune serum than did the other procedures, while 

 the administration of antigen by way of the blood, or into the tra- 

 chea or pleura, caused the rabbits to yield serum containing pro- 

 tective antibody, whereas the serum from rabbits treated subcu- 

 taneously failed to confer passive protection on mice. 



In communications published in 1924, 192T, and 1930, Still- 

 man 1330 " 2 ' 1334 ~ 5 supplied additional information concerning the 

 nature and degree of the immune response in mice and rabbits re- 

 sulting from inhalation, and from the subcutaneous, intramuscu- 

 lar, and intravenous application of both living and dead pneumo- 

 cocci. The serum of 80 per cent of rabbits injected intravenously 

 with fixed amounts of heat-killed pneumococci and the serum of 60 

 per cent of the animals injected intraperitoneally with similar 

 doses contained agglutinins and all showed protective antibodies. 

 Of rabbits receiving intramuscular injections, the serum of only 33 



