1/2 ADDENDUM 



A number of investigations with these objects have recently 

 been carried out, particularly in America, mostly since the first 

 edition was written, and it may be of assistance to discuss, 

 rather more in detail than in the text, how far these investiga- 

 tions have yielded results capable of practical application. 



From this point of view these tests may be classified into 

 three groups haemolytic and virulence tests ; fermentation 

 reactions ; other tests. 



I. Haemolytic and virulence tests. The haemolytic test for 

 differentiating streptococci was first introduced by Schotmiiller. 

 He used a blood-agar medium and separated the streptococci 

 by this means into three groups, i.e. : 



(1) Streptococcus pyogenes vel erysipelatos. A long chain 

 form with greyish colonies and with a zone of haemolysis. 



(2) Streptococcus mitior. A short chain form with greenish 

 colonies producing very slight haemolysis. 



(3) Streptococcus mucosus. Capsulated organisms with 

 colonies of a mucous, slimy consistency. No haemolysis. 



Two distinct methods have been used to carry out this 

 test. 



(a) Blood-agar plates. Schotmiiller used a medium con- 

 sisting of two parts sterile human blood mixed with five parts 

 of ordinary agar. Other observers have used animal blood. 

 Stowell, Hilliard and Schlesinger \ for example, added a few 

 drops of fresh sterile rabbit's blood to cooled melted agar tubes, 

 the contents after mixing being poured into Petri dishes in 

 the ordinary way. Haemolysis is tested by streaking the plates 

 from a young culture. 



Other workers have used ordinary blood-agar medium, the 

 blood being smeared over the surface of the agar. This method 

 was employed by Hopkins and Lang, but has the drawback 

 that the degree of haemolysis in part depends upon the 

 thickness of the blood layer. 



1 To save repetition references are given at the end of this section. 



