342 APPLICATION OF METHODS OF BACTERIOLOGY 



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 pathological process from which it was derived. 



There is never any certainty of faithfully reproducing, by 

 inoculation into susceptible animals, the pathological lesion 

 from which a culture of the organism may have been ob- 

 tained. The introduction into a susceptible animal of a 

 culture derived from either a spreading phlegmon or an 

 erysipelatous inflammation may result in erysipelas, general 

 septicemia, local abscess-formation, or, as said, may have 

 no effect 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 cultivation 

 fully virulent varieties of streptococcus pyogenes usually 

 lose their virulence after a short time. Petruschky' 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^ 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-fluid 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 exists 

 between virulence and the length of the chains formed by 

 streptococci when growing in fluid media. It is held that 



' Centralblatt fur Bakteriologie und Parasitenkunde, 1895, Abth. i, Bd. 

 xvii. 



" Annales de I'liistitut Pasteur, 1895. 



