330 BIOLOGY OF PNEUMOCOCCUS 



bodies. Additional evidence confirming the efficacy of heat-killed 

 antigens is to be found in the experiments of Stillman and Good- 

 ner. 1342 Three intravenous injections at four-day intervals of saline 

 suspensions of heat-killed cultures of Type I, II, and III pneumo- 

 cocci protected rabbits against an otherwise fatal infection of 

 pneumococci of the corresponding type administered according to 

 Goodner's intradermal technique. The results were controlled by 

 the demonstration of agglutinins and protective antibodies in the 

 serum of the treated animals. 



In 1923, Yoshioka, 1562 finding that the successful immunization 

 of mice was largely dependent upon the total mass as well as the 

 spacing of the doses of antigen, devised a rapid method involving 

 small quantities of heat-killed pneumococci injected in six half- 

 hourly doses. In this way he obtained excellent protection in mice. 

 In the next year, Killian 704 repeated Yoshioka's experiments with 

 intensive serial injections and, in addition, tried injections of 

 killed cultures with weekly intervals between each series. By this 

 plan of three series of intraperitoneal injections at weekly inter- 

 vals, it was possible to render mice immune to a fatal dose of pneu- 

 mococci given three days after the completion of the immunizing 

 treatment, but the immunity lasted only a few weeks. Killian laid 

 stress on the proper amount of antigen to be given, because doses 

 too small or too large yielded poorer results. The use of living, 

 fully virulent organisms, contrary to the experience of most ob- 

 servers, resulted in a noticeably lower degree of immunity. 



In another communication, Killian 706 gave the details of further 

 experiments from which it appeared that by employing the intra- 

 venous route for serial injections the level of protection in mice 

 could be elevated, and that by periodic intraperitoneal treatment 

 of the animals with four-day intervals between injections of in- 

 creasing doses of killed vaccine one could obtain a high degree of 

 protection in a short time. In a third communication, Killian 707 de- 

 scribed a refractory stage which lasted for several days after an 

 immunizing injection and, in order to avoid this stage and to se- 



