STREPTOCOCCUS PYOGENES 



339 



appearance and luxuriant in development. In glucose-ascitic-agar, 

 acid formation from the sugar causes coagulation of albumin with 

 the consequent formation of flaky white precipitates throughout the 

 medium.' 



In gelatin stab-cultures growth takes place slowly, appearing after 

 twenty-four to thirty-six hours as a very thin white line, or as discon- 

 nected little spheres along the line of the 

 stab. The colonies on gelatin plates are 

 similar in form to those on agar, but are 

 usually more opaque and more distinctly 

 white. The gelatin is not liquefied by the 

 pyogenic streptococci, though certain of 

 the more saprophytic forms may occa- 

 sionally bring about slow fluidification. 



On Loeffier's coagulated blood serum, 

 growth is rapid and luxuriant, and may 

 show a slight tendency to confluence if 

 the medium is very moist. Good chain 

 formation takes place on this medium. 



Upon potatoes, growth is said not to 

 take place.^ 



On media containing red blood cells, 

 most pathogenic streptococci cause hemolysis and decolorization (see 

 Fig. 74, p. 345). It is useful to remember this when examining 

 blood-culture plates, for here the yellow transparent halo of hemo- 

 lysis and decolorization surrounding the colonies may aid in differenti- 

 ating these bacteria from pneumococci. This is of especial importance, 

 since many streptococci, when cultivated directly out of the human 

 blood, do not exhibit chain formation, but appear as diplococci. 



In the inulin-serimi media of Hiss,^ streptococci do not produce 

 acid and coagulation. The so-called Streptococcus mucosus, a capsule- 

 bearing, inulin-fermenting microorganism, is very probably a sub-species 

 of the pneumococcus (see later section). 



Resistance. — Streptococci on the ordinary culture media, without 

 transplantation and kept at room temperature, usually die out within 

 ten days or two weeks. They may be kept alive for much longer periods 

 by the use of the calcium-carbonate-glucose bouillon, if the cultures are 



' Libman, Medical Record, Ivii, 1900. 



' Frosch und Kolle, in Fliigge, "Die Mikroorganismen," 1891. 



« Hiss, Jour. Exp. Med., vi, 1905. 



Fig. 73. — Strbptococcus Col- 

 onies, ON Sektjm Agar. 



