ANTIBODIES TO PNEUMOCOCCUS 403 



aplastic rabbits recovered. Winternitz and Kline accordingly 

 concluded that the immunological response was dependent upon at 

 least three factors, namely, immune bodies, white blood cells, and a 

 third factor relying for its existence on the presence of white 

 blood cells at the time of inoculation with Pneumococcus. The hu- 

 moral immune bodies acted in causing the immediate disappear- 

 ance of the injected organisms from the circulation, but the third 

 factor, originating in the leucocytes, appeared to be essential to 

 the recovery of the infected animal. 



The importance of elements peculiar to immune serum for the 

 protection of mice was shown by Tilgren (1915) 14012 who, by add- 

 ing immune sheep serum and sheep leucocytes to an infective dose 

 of pneumococci, protected rabbits against infection. In mice, the 

 immune serum afforded protection but the addition of heterolo- 

 gous leucocytes resulted in no increase in the protective power of 

 the serum. 



More detailed information regarding the tissues concerned in re- 

 sistance to pneumococcal infections is to be found in the communi- 

 cation of Permar (1923), 1082 who believed that the mononuclear 

 phagocytic cells appearing in the exudate in acute experimental 

 pneumonia in the rabbit were of vascular endothelial origin. Other 

 cells of visceral origin possibly contributed in some degree to the 

 total number of phagocytes in the exudate. Dust cells of similar 

 origin already present in the alveoli also might act as phagocytes 

 in inflammatory reactions, while interstitial dust cells could be- 

 come reactivated and through liberation by inflammatory edema 

 were enabled to appear in the exudate. The entire group of cells, 

 therefore, including the newly produced phagocytes and the dust 

 cells, may take part in the reaction to the invading pneumococci. 



Singer and Adler (1924), 1290 after studying the response in rab- 

 bits to infection with Type III Pneumococcus, believed that the 

 defensive factors resided in the reticuloendothelial system, and 

 that the histocytes of bone marrow, the capillary endothelia of the 

 parenchymatous organs, the endothelium of serous cavities, and 



