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 septicemia 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 been 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 
