564 STREPTOCOCCUS 



Metabolic Activities.- — Most of the early attempts to classify the streptococci 

 were based on their fermentation reactions in an empirically selected series of 

 substrates. The behaviour of the different members of this genus in blood- 

 containing media has, however, come to occupy so important a place as a criterion 

 for primary classification, that it will be convenient to deal with it first. 



Classification Based on Changes Produced in Blood. 



Blood Plates. — Marmorek (1895) first noted the ability of certain strains of 

 streptococci to lyse red blood corpuscles in vivo and in vitro, but it was Schott- 

 miiller (1903) who proi^osed that the ability to produce haemolysis in vitro should 

 be adopted as a differential criterion for purposes of classification. He noted 

 that certain strains of streptococci produced clear zones of lysis when grown on 

 blood agar plates, while others gave colonies which were surrounded by zones 

 of greenish discoloration. For the former type Schottmiiller proposed the name 

 Str. hcBmolyticus, for the latter Str. viridans. These observations formed the basis 

 of a system of classification and nomenclature which has been developed by many 



Fig. 123. — Str. pyogenes. Fig. 124. — Viridans streptococci. 



Deep colony in blood agar plate, showing Deep colonies in blood agar plate, showing 



wide zone of complete htemolysis, and the zone of discoloured cells round colony, 



sharply differentiated margin of the colony obscuring margin, and zone of incomplete 



— jS-hsemolysis ( X 8). lysis beyond — a-haemolysis ( X 8). 



subsequent investigators. It has, indeed, been shown that the green-producing 

 streptococci are not devoid of hsemolytic activity, though the zones which they 

 produce on blood agar plates are different in kind, as well as in extent, from those 

 formed round the colonies of the frankly heemolytic strains. Mandelbaum (1907) 

 emphasized the importance of microscopical examination of the colonies formed 

 on blood agar plates, and noted that, while the colonies of the long pathogenic 

 streptococci were surrounded by clear colourless zones, those of the viridans type, 

 and also those of the pneumococcus, were surrounded by a zone of discoloured, 

 non-hsemolysed corpuscles lying immediately next the colony, and an outer narrow 

 hsemolysed zone containing only corpuscular shadows. 



These phenomena were studied in much greater detail by Smith and Brown 

 (1915), and by Brown (1919). The monograph by Brown, in which the appearances 

 met with and the factors which determine or modify them are fully discussed, 

 contains an admirable review of the literature dealing with the classification of 

 streptococci up to 1919. In this monograph great emphasis is laid on the importance 

 of employing a uniform and standardized technique, and, in particular, on the 



