I50 MICRO-ORGANISMS AND DISEASE [chap. 



— that is, the power to produce typical erysipelas in the rabbit's 

 ear — becomes less and less and ultimately is lost. But 

 by starting a fresh culture on solidified blood-serum and 

 using then a somewhat large dose erysipelas in the ear can 

 be again produced, the lymph of this ear and its cultures 

 again being capable of producing typical erysipelas. Until 

 streptococcus pyogenes obtained from abscess or common 

 phlegmon can be shown to produce in the rabbit's ear the 

 same typical progressive erysipelas as can the lymph of 

 erysipelas and the culture therefrom it must be held that the 

 two are distinct species. The facts that streptococcus pyo- 

 genes in its virulent varieties can produce a phlegmon in the 

 rabbit's ear, and that streptococcus erysipelatos by subcultures 

 loses so much of its virulence as to produce not erysipelas 

 but only phlegmon, do not justify considering the two 

 as interchangeable ; as far as I am aware, streptococcus 

 pyogenes has not been so changed as to be capable of pro- 

 ducing erysipelas in the rabbit's ear, whereas the attenuated 

 form of streptococcus erysipelatos can be readily brought back 

 to its former virulence, i.e. the power to produce typical 

 erysipelas. Streptococcus erysipelatos occurs as a complica- 

 tion in typhoid fever in perforation ; then the peritoneal 

 fluid and the blood contain numerous streptococci the culture 

 of which produces in rabbits typical erysipelas. The name 

 "streptococcus erysipelatos " must therefore be reserved for 

 that species of streptococcus which is found in genuine human 

 erysipelas, and which can set up in the rabbit's ear typical 

 spreading erysipelas, and must not be mixed up with strepto- 

 coccus pyogenes, however much morphologically and cultur- 

 ally the two approach one another. 



6. The same may be said of the streptococcus, which I 

 described, of the contents of the vesicles and of the ulcers 

 in foot-and-naouth disease of sheep. In culture it resernbles 



