VIRULENCE OF STREPTOCOCCUS PYOGENES. 155 



cular condition which healed only after some weeks. Con- 

 firmatory experiments of this nature have been made by 

 Bockhart, Bumm, and others. 



When tested experimentally the staphylococcus pyogenes 

 albus has practically the same pathogenic effects as the 

 staphylococcus aureus. 



The streptococcus pyogenes is an organism the virulence of 

 which varies much according to the diseased condition from 

 which it has been obtained, and which also loses its viru- 

 lence rapidly in cultures. Even highly virulent cultures, if 

 grown under ordinary conditions through several genera- 

 tions, in the course of time almost lose any pathogenic 

 power. By passage from animal to animal, however, the 

 virulence may be much increased, &b& pari passti the effects 

 produced by it are correspondingly varied. Marmorek, 

 for example, has found that its virulence can be enor- 

 mously increased by growing it alternately (a) in a mixture 

 of human blood serum and bouillon (vide page 50), and 

 (b} in the body of a rabbit, till ultimately it possesses a 

 supervirulent character, so that even a few streptococci 

 introduced into the tissues of a rabbit produce rapid 

 septicaemia with death in a few hours, the organisms being 

 found in large numbers in the internal organs. It has 

 been proved by Marmorek's experiments and those of 

 others that the same streptococcus may produce at one 

 time merely a passing local redness, at another a local 

 suppuration, at another a spreading erysipelatous condition, 

 or again a general septicaemic infection, according as its 

 virulence is artificially increased. Such experiments are 

 of extreme importance as explaining to some extent the 

 great diversity of lesions in the human subject with which 

 streptococci are associated. 



Varieties of Streptococci. It may be stated here that 

 formerly the streptococcus pyogenes and the streptococcus 

 erysipelatis were regarded as two distinct species, and 

 various points of difference between them were given. 

 Further study, and especially the results obtained by 

 modifying the virulence, have shown that these distinctions 



