Streptococcus Pyogenes 311 



while numerous small flocculi are suspended in it, sometimes ad- 

 hering to the sides of the tube, sometimes forming a sediment. 

 When the flocculi formation is distinct, the name Streptococcus con- 

 glomeratus (Kurth) is sometimes given to the organism; when the 

 medium is difiusely clouded, it is called Streptococcus diffusus. 



In mixtures of bouillon and blood-serum or ascitic fluid the strep- 

 tococcus grows more luxuriantly, especially at incubation tempera- 

 tures, distinctly clouding the liquid. As the lactic acid which is 

 rapidly formed inhibits the growth of the cocci, Hiss recommends* 

 that instead of eliminating the sugars in the broth, upon which the 

 streptococci . are nourished, i per cent, of sterile powdered CaCOs 

 be added to the culture-media. This neutralizes the acid as rapidly 

 as it is formed. It also maintains the life of the culture for a long 

 time. 



Milk. — The organism seems to grow well in milk, which is coagu- 

 lated and digested. 



Reaction. — The streptococcus is sensitive to acids, and can only 

 grow well in media with a slightly alkaline reaction. All strepto- 

 cocci produce acids and eventually acidulate the media, thus check- 

 ing their further development. 



Vital Resistance. — The optimum temperature appears to be in the 

 neighborhood of 37°C. It grows well between 25° and 40°C., above 

 40.s°C. the growth is slowed. The thermal death point is low. 

 Sternberg found that the streptococci succumb at temperatures of 

 52° to S4°C. if maintained for ten minutes. Their vitality in culture 

 is slight, and unless frequently transplanted they die. Bouillon 

 cultures usually die in from five to ten days. On solid media they 

 seem to retain their vegetative and pathogenic powers much longer, 

 especially if kept cool and cultivated beneath the surface of the 

 medium in a deep puncture. They resist drying fairly well. 



Differential Features. — It is not always easy to differentiate 

 Streptococcus pyogenes from other less important forms of strep- 

 tococci and from the pneumococcus. One of the best methods is 

 by the employment of blood-agar plates, suggested by Schottmiiller.f 

 Such plates are easily prepared by melting ordinary culture agar- 

 agar, cooling to about 4S°C., and then adding about 0.5 cc. of de- 

 fibrinated human or rabbit's blood to the tube. The blood is first 

 thoroughly mixed with the agar, then the tube inoculated, and poured 

 into a Petri dish. As the Streptococcus pyogenes grows, it produces 

 a hemolytic substance that destroys the blood-corpuscles in the 

 vicinity of the colony, thus surrounding each by a clear, pale halo 

 that contrasts with the red agar. The colonies themselves appear 

 gray. 



The test is not specific, and Ruedigerf points out that the diph- 



4: (( 



Text-book of Bacteriology," p. 338. 

 t "Miinch. med. Wochenschrift," 1903, l, p. 909. 

 I "Jour. Amer. Med. Assoc," 1906, XLVii, p. 1171. 



