Streptococcus Pyo genes 353 



In mixtures of bouillon and blood-serum or ascitic fluid 

 the streptococcus grows more luxuriantly, especially at in- 

 cubation temperatures, 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 CaCO 3 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 

 coagulated and digested. 



Reaction. The streptococcus is sensitive to acids, and 

 can only grow well in media with a slightly acid reaction. 

 All streptococci produce acids and eventually acidulate the 

 media, thus checking 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 40.5 C. the growth is slowed. The 

 thermal death point is low. Sternberg found that the 

 streptococci succumb at temperatures of 52 to 54 C. if 

 maintained for ten minutes. Their vitality in culture is 

 slight, and unless frequently transplanted they die. Bouil- 

 lon 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. 



Differential Features. It is not always easy to dif- 

 ferentiate Streptococcus pyogenes from other less impor- 

 tant forms of streptococci and from the pneumococcus. 

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

 plates, suggested by Schottmuller.t 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 

 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 sur- 



*" Text-book of Bacteriology," p. 338. 



f "Munch, med. Wochenschrift, " 1903, L, p. 909. 



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