STREPTOCOCCUS PYOGENES. 481 



posure, two hours): Mercuric chloride, 1 : 2500; sul- 

 phate of copper, 1 : 200; trichloride of iodine, 1 : 750; 

 peroxide of hydrogen, i : 50; carbolic acid, 1 : 300; 

 cresol, 1 : 250; lysol, 1 : 300; creolin, 1 : 130. 



Pathogenesis. The majority of test animals are not 

 very susceptible to infection by the streptococcus, and, 

 hence, it is difficult to obtain any definite pathological 

 alterations in their tissues through the inoculation into 

 them of cultures of this organism by any of the methods 

 ordinarily practised. White mice and rabbits, under 

 similar conditions, are the most susceptible, and these 

 animals are, therefore, usually employed for experimen- 

 tation. Streptococci, however, differ greatly in the 

 effects which they produce in inoculated animals, 

 according to their animal virulence, which is very 

 different from human virulence. The most virulent, 

 when injected in the minutest quantity into the circu- 

 lation or into the subcutaneous tissues of a mouse or 

 rabbit, produce death by septicaemia. Those of some- 

 what less virulence produce the same result when in- 

 jected in considerable quantities. Those still less patho- 

 genic produce septicaemia, which may be mild or severe, 

 when injected into the circulation; but when injected 

 subcutaneously, they produce abscess or erysipelas. 

 The remaining streptococci, unless introduced in quan- 

 tities of 20 c.c. or over, produce only a slight redness, 

 or no reaction at all, when injected subcutaneously, 

 and little or no effect when injected directly into the 

 circulation. Many of the streptococci obtained from 

 cases of cellulitis, abscess, empyema, and even septi- 

 caemia belong to this group. 



A number of varieties of streptococci have thus been 

 discovered, differing in virulence and in their growth 



31 



