STREPTOCOCIC 51 



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 strepto- 

 cocci, next to that of pathogenicity, is the occurrence of long or short 

 chains, the virulent ones tending to appear in chains of from ten to 

 twenty cocci, while the normal inhabitants of the nose, mouth and 

 faeces generally tend to be in shorter chains. 



FIG. ii Streptococcus pyogenes. (Kolle and Wassermann.) 



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

 but may be restored either by inoculating streptococci along with 

 various 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 in- 

 serted in the vein it will be difficult to force in the material and a swell- 

 ing will immediately show itself. 



Besides the morphological and pathogenic variations, Schottmuller 

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

 blood and 3 to 6 parts of agar. On this medium Strep, erysipelatis 

 has a hemolytic action, the laking of the red cells bringing about a more 

 or less clear ring surrounding the colony. The short-chain strepto- 

 cocci do not have a hemolytic halo. The pneumococcus has a 



