346 PROTECTIVE INOCULATIONS. 
fauces, and certain acute abscesses are due to infection by a strepto- 
coccus described by recent authors under the name of Streptococcus 
pyogenes. This streptococcus, like other pathogenic microdrganisms 
of the same class, varies greatly in its pathogenic power as a result of 
conditions relating to the source of the particular variety under culti- 
vation. As obtained from a case of erysipelas or puerperal fever it is 
extremely virulent, but when it has led a saprophytic existence for 
some time, or has been cultivated for a considerable time in the 
usual artificial culture media, its pathogenic potency is greatly 
diminished. 
Mironoff (1893) has made a series of experiments with a view to 
determining whether rabbits can be immunized against the pathogenic 
action of this streptococcus, and has obtained successful results by the 
following method: 
Vigorous rabbits, weighing two kilogrammes, were inoculated 
subcutaneously with from three to six cubic centimetres of a sterilized 
bouillon culture of the streptococcus. Cultures three days old were 
employed, and these were sterilized for twenty minutes at 120° C.— 
the reason for using so high a temperature is not apparent, inasmuch 
as this streptococcus is destroyed in a few minutes by a temperature 
of 60° C. At the end of ten to fifteen days, ‘when the animal has 
fully recovered,” a second dose of from six to twelve cubic centimetres 
of a culture, sterilized in the same way, is injected beneath the skin. 
After another interval of ten to fifteen days two cubic centimetres of a 
virulent non-sterilized culture are injected subcutaneously, and this is 
repeated with gradually increasing doses (one to two cubic centime- 
tres more) at intervals of the same period. Finally the animals 
“support without reaction” a dose five times as great as would be re- 
quired to kill an animal of the same weight not immunized. But the 
author adds that more than half the animals thus treated died before 
the completion of the immunizing process. These deaths resulted 
from local infectious processes, such as peritonitis, pericarditis, men- 
ingitis, or abscesses formed at the point of inoculation. 
Further experiments showed that the blood serum of animals im- 
munized in this way when injected into susceptible animals (rabbits) 
in the dose of 1.5 cubic centimetres per kilogramme of body weight 
conferred upon them a certain degree of immunity against streptococ- 
cus infection, and with twice this amount (three cubic centimetres) a 
very decided immunity was produced. The blood serum of immune 
rabbits in doses of three to four cubic centimetres per kilogramme of 
body weight was found to exercise a curative power, and completely to 
arrest the acute septicemia resulting from inoculations with a virulent 
