VIRULENCE IN STREPTOCOCCI 59 



The essential point to bear in mind is that the finding of a strepto- 

 coccus does not necessarily explain an infection, because normally 

 streptococci are among the organisms most frequently and abundantly 

 found in plates made from normal buccal and nasal secretions. It is 

 well to be very conservative When reporting streptococci as the etiolog- 

 ical factor from lesions of the throat or nose. 



Probably the most practical point in the differentiation of streptococci, next to 

 that of pathogenicity, is the occurrence of long or short chains, the virulent ones 

 tending to appear in chains of from 10 to 20 cocci, while the normal inhabitants of 

 the nose, mouth and faeces generally tend to be in shorter chains. 



As regards virulence, this is exceedingly variable it is soon lost, but 

 may be restored either by inoculating streptococci along with various 



FIG. 12. Streptococcus pyo genes, (Kolle and W assermann.) 



other organisms or by passage through successive rabbits. The rabbit 

 is the most susceptible animal and should be inoculated in one of the 

 prominent ear veins. If the needle of the syringe is not inserted in 

 the vein it will be difficult to force in the material and a swelling will 

 immediately show itself. 



Recently isolated cultures from human infections are not very virulent for animals. 

 Passage through the rabbit, however, enormously increases the virulence. It may 

 be more convenient to inoculate a mouse at the root of the tail. If the culture is 

 very virulent, it becomes generalized and death occurs in two or three days. If less 

 virulent, a local abscess forms. 



Besides the morphological and pathogenic variations, Schottmuller 

 has noted differences where these organisms are grown on i part of 



