MICROCOCCUS LANCEOLATUS. 513 



Judging from the streptococcus, the use of a specific 

 bactericidal serum developed from a single pneumo- 

 coccus will probably show that some of the organisms 

 ranked as pneumococci are not influenced by it. 



Immunity. Early in the history of this organism 

 experiments were begun for the production of immunity 

 in animals by means of preventive inoculations. 

 Fraenkel showed that subcutaneous injections of rab- 

 bits with virulent cultures of the diplococcus produced 

 infection in only a small percentage of these animals, 

 which either died from septicaemia or after a time re- 

 covered. In the latter case they were found to be some- 

 what immune to a second infection. Later experiments 

 were conducted on the same principle, the object being 

 to repeatedly slightly infect the animal, and thus to 

 gradually increase its power of resistance to infection. 

 For this purpose either artificially attenuated cultures 

 or material containing naturally attenuated micrococci 

 were used for inoculation. Cultures artificially attenu- 

 ated by heat or several days' growth in the incubator, 

 sputum taken from a pneumonic patient after the crisis, 

 rusty sputum obtained before the crisis and heated to 

 60 C., old pleuritic exudation containing attenuated 

 bacteria, etc., have thus bejen repeatedly employed. 



Another series of experiments were based on the 

 assumption that the immunizing substances are con- 

 tained in the natural or artificial products of the growth 

 of the organism. Thus cultures which were freed from 

 bacteria by filtration, and emulsions of pneumonic 

 sputum, portions of pneumonic lung, pleuritic exuda- 

 tions, etc., were employed by different experimenters. 

 The quantity of material required for inoculation being 

 found inconveniently large, attempts were then made 



33 



