492 BIOLOGY OF PNEUMOCOCCUS 



mechanism of the vaccinated person has been operating in the pro- 

 duction of immunity. 



On this basis, Howell 661 determined the agglutinative, comple- 

 ment-fixing, and protective titer of the serum of three healthy men 

 who had received by subcutaneous injection one cubic centimeter 

 of the American Army lipovaccine, containing 0.83 milligram of 

 dried pneumococcal protein of Types I, II, and III. There was a 

 definite rise in agglutinins in the second week after injection, the 

 height being reached from the second to fourth week, although the 

 antibody was still demonstrable from three to nine months. The 

 complement-fixation reaction with the subjects' serum became 

 positive from the seventh to the fifteenth day, was strongest at 

 the twenty-fifth day, and still was positive over the period during 

 which agglutinins were shown to endure. The content of protective 

 antibodies in the serum more or less paralleled that of agglutinins. 



When heat-killed vaccines were administered intravenously in 

 rabbits and the animals subsequently tested by intradermal inocu- 

 lation, Stillman and Goodner 1342 showed that the immune effects 

 persisted for a somewhat longer time. In the case of Type I vac- 

 cines, the resistance induced appeared to be high ten days after the 

 completion of the course of injections, then to become irregular in 

 degree and generally lower during the next four months. After the 

 seventh month, the level of resistance dropped again and was usu- 

 ally low. The content of protective antibodies paralleled the de- 

 gree of resistance of the animals throughout the period of observa- 

 tion but the agglutinin titer of the treated animals' serum was high 

 only during the first two months. With Type II vaccines, the re- 

 sistance to infection was somewhat lower than that evoked by 

 Type I vaccine, but remained moderately high for nine months 

 with an abrupt decrease after that period. Treatment with Type 

 III preparations resulted in a fairly marked degree of resistance 

 during the first month, which, however, diminished sharply and re- 

 mained low. None of the animals treated with Type III vaccine 

 exhibited agglutinins or protective antibodies in the serum. While 



