298 Wound Infection; Suppuration 



given to the organism ; when the medium is diffusely clouded, 

 it is called Streptococcus difjusus. 



In mixtures of bouillon and blood-serum or ascitic fluid 

 the streptococcus grows more luxuriantly, especially at in- 

 cubation temperatures, distinctly clouding the liquid. 



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

 coagulated and digested. 



Reaction. The streptococcus is not very sensitive to 

 acids, and can be grown quite well in media with a slightly 

 acid reaction. All streptococci produce acids and event- 

 ually acidulate the media. 



Vital Resistance. The optimum temperature appears to 

 be in the neighborhood of 37 C. It grows well between 

 25 and 40 C. ; above 40.5 the growth is slowed. The 

 thermal death point is low. Sternberg found that the 

 streptococci succumb at temperatures of 52-54 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 well. The growth in artificial media is accompanied 

 by the production of an acid which probably acts destruc- 

 tively upon the bacteria themselves, and first inhibits further 

 growth, then destroys them. 



Differential Features. It is not always easy to dif- 

 ferentiate Streptococcus pyogenes from other less impor- 

 tant forms of streptococci and from the pneumococciis. 

 One of the best methods is by the employment of blood-agar 

 plates suggested by Schottmiiller.* Such plates are easily 

 prepared by melting ordinary culture agar-agar, cooling to 

 about 45 C., and then adding about 0.5 c.c. of defibrinated 

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

 oughly 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 sur- 

 rounding 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 



* "Miinch. med. Wochenschrift," 1903, L, p. 909. 

 t "Jour. Amer. Med. Assoc.," 1906, XLVII, p. 1171. 



