482 BACTERIOLOGY. 



on artificial media; but all attempts to separate them 

 into various classes, until recently through the use of 

 specific serum, have failed, because the differences ob- 

 served, though often marked, are not constant, many 

 varieties having been found to lose their distinctive 

 characteristics, and even to apparently change from one 

 class to another. A further objection to any previous 

 classification of streptococci, based on the manner of 

 growth on artificial culture media, is that it has been 

 impossible to make any which would at the same time 

 give even an approximate idea of their virulence. Ex- 

 periments have proved that the streptococci originally 

 virulent may become non-virulent after long cultivation 

 on artificial media, and, again, that they may return to 

 their original properties after being passed through the 

 bodies of susceptible animals. The peculiar type of 

 virulence which they may acquire tends to perpetuate 

 itself, at least for a considerable time. 



One important fact that experience teaches us is, 

 that those streptococci are the most dangerous to any 

 animal which have come immediately from septic con- 

 ditions in the same species of animal, and the more 

 virulent the case the more virulent the streptococci are 

 apt to be in other animals of the same species. There 

 seems also to be a strong tendency for a streptococcus 

 to produce the same inflammation, when inoculated, as 

 the one from which it was obtained; for example, strep- 

 tococci from erysipelas tend to produce erysipelas, from 

 septicaemia to produce septicaemia, etc. Streptococci, 

 however, obtained from different sources (abscesses, 

 puerperal fever, sepsis, erysipelas, etc.) are in many 

 instances capable, under favorable conditions, of pro- 

 ducing erysipelas when inoculated into the ear of a 



