STREPTOCOCCUS PYOGENES. 281 



cultures from other sources exhibit the most marked 

 pathogenic properties, even when employed in almost 

 infinitesimal quantities. Between these extremes every 

 gradation may be expected. The virulence of a culture 

 as exhibited upon animals under experiment is not 

 necessarily proportional to the intensity of the patho- 

 logical process from which it was derived. 



There is never any certainty of faithfully repro- 

 ducing, by inoculation into susceptible animals, the 

 pathological lesion from which a culture of the organ- 

 ism may have been obtained. The introduction into a 

 susceptible animal of a culture derived from either a 

 spreading phlegmon or an erysipelatous inflammation 

 may result in erysipelas, general septica3mia, local ab- 

 scess-formation, or, as said, may have no eifect at all. 

 Cultures may be encountered that are pathogenic for 

 one susceptible species of animals and not for another. 



Under the ordinary conditions of artificial cultiva- 

 tion fully virulent varieties of streptococcus pyogenes 

 usually lose their virulence after a short time. 

 Petruschky l preserves this property by cultivation 

 upon nutrient gelatin for two days at 22 C., keeping 

 the cultures after this time in the refrigerator, and 

 transplanting upon fresh gelatin every five or six days. 

 Marmorek 2 finds the virulence preserved by growing 

 the organism in a mixture of 2 parts of horse or 

 human blood-serum and 1 part of nutrient bouillon, or 

 of 1 part of ascites-fl uid and 2 parts of bouillon. 



Its virulence may sometimes be increased by passage 

 through a series of susceptible animals. 



Certain authors are of the opinion that a relation 



1 Petruschky : Centralblatt fiir Bakteriologie und Parasitenkunde, 

 3885, Abth. i. Bd. xvii. 



2 Marmorek : Annalew de 1'Institut Pasteur, 1895. 



