408 PATHOGENIC MICROORGANISMS 



groups as follows: I. Streptococcus longus or haemolyticus, consisting 

 of the more virulent varieties, with tendency to form long chains, and 

 producing hemolysis upon blood media. II. Streptococcus mitior or 

 viridans, including less virulent strains, with usually shorter chain- 

 formation, and producing green, non-hemolyzing colonies upon blood 

 media. A third group, Streptococcus mucosus, will receive special con- 

 sideration in a separate section, and is probably more closely related 

 to the pneumococci. 



Another nomenclature has recently been suggested by Smith and 

 Brown. 19 These workers disapprove of the use of the name "strep- 

 tococcus viridans" for the less hemolytic streptococci because many 

 of them actually produce little or no green color on blood agar, 

 and all of them did produce more or less hemolysis. They describe; 

 two types of streptococci with reference to hemolysis, calling the 

 less hemolytic the "Alpha" type, and the markedly hemolytic the 

 "Beta" type. A third type, "Gamma," produces neither discolora- 

 tion nor hemolysis. They describe them as follows : 



Type Alpha. As observed after forty-eight hours incubation the change 

 produced may be described as a somewhat greenish discoloration and partial 

 hemolysis immediately surrounding the colony, forming an indefinitely 

 bounded zone, 1 to 2 millimeters in diameter, and surrounded by a second 

 narrow clearer and not discolorized partially hemolyzed zone. 



Type Beta. Streptococci of this type produce hemolyzed zones on horse 

 blood agar plates, radically different from those of the Alpha type. They 

 produce clear transparent, completely hemolyzed colorless zones, 2 to 4 milli- 

 meters in diameter after forty-eight hours. 



Type Gamma. By this they mean streptococcus strains which grow within 

 and on blood agar plates without the production of perceptible hemolysis 

 or discoloration. Such strains are those described by Mandelbaum as strep- 

 tococcus saprophyticus and correspond to some of the Rosenow types. 



Smith and Brown 19 call attention to the great care which is 

 necessary in regard to details of cultivation for observing strep- 

 tococci for their hemolytic properties on blood plates. They con- 

 tradict Ruediger's assertion that the formation of acid in such plates 

 may give rise to the greenish coloration. There is no essential dif- 

 ference in result between plates made of defibrinated horse, rabbit 



19 Smith and Brown, Jour. Med. Res., 31, 1914, 455, and Monograph of Rock 

 Inst,, No. 9, January, 1919. 



