IMMUNISA TION A GAINST PNE UMOCOCCUS. 221 



occur in the sputum after the crisis of the disease. Netter 

 effected immunisation by injecting an emulsion of the dried 

 spleen of an animal dead of pneumococcus septicaemia. 

 Here the cocci were attenuated by the drying. Virulent 

 cultures killed by heating at 62 C. have also been used, 

 immunisation being here accomplished by the intracellular 

 toxines. The Klemperers found that injection of rusty 

 sputum kept at 60 C. for one to two hours and then 

 filtered, and of toxine similarly treated, had a like result. 

 In all cases one or two injections of the modified bacteria 

 or toxine were sufficient for immunisation. It was three 

 days in the case of intravenous injection, and fourteen days 

 in the case of subcutaneous injection, before immunity was 

 established, and the latter lasted a month or more. The 

 immunity was accompanied by the development in the 

 blood of antitoxic substances which had no effect either 

 outside or inside the body in killing the pneumococci, but 

 merely * neutralised their toxines. Such antitoxines not 

 only protected a rabbit against subsequent inoculation with 

 pneumococci, but if injected within twenty-four hours after 

 inoculation, prevented death. 



These results have been generally confirmed by later 

 observers. In this connection an interesting fact observed 

 by Mennes may be noted, namely, that normal leucocytes 

 only become phagocytic towards pneumococci when they 

 are lying in the serum of an animal immunised against 

 this bacterium. 



The production of antitoxines may shed new light on 

 what occurs in man in the case of recovery from pneumonia. 

 The view has been advanced that the crisis so character- 

 istic of a non-fatal case of the disease takes place when the 

 balance of antitoxine against toxine is in favour of the 

 former. The pneumococci after the crisis, as has been 

 proved both culturally and by inoculation experiments, are 

 still vital and virulent, though not so virulent as when the 

 fever is at its height. On them directly the antitoxine has no 

 effect, but any toxine now elaborated by them is neutralised, 

 and has no longer either local or general pathogenic effects. 



