THE STREPTOCOCCUS GROUP 271 



from lesions or from animals, exhibit a delicate stainable zone around 

 individual organisms or pairs of organisms, which suggests capsules. 

 Howard and Perkins 1 have isolated such an organism which exhibited 

 a very definite capsule. It grew habitually in short chains in fluid 

 media, the individuals occurring typically in pairs. The organism 

 is closely related to the pneumococcus, and Dochez and Gillespie 2 

 have named it Pneumococcus mucosus. 



Streptococcus pyogenes stains readily with ordinary anilin dyes. 

 It is typically Gram-positive, although old cultures may fail to retain 

 the Gram stain. The saprophytic types frequently are Gram-negative. 



Isolation and Culture. Streptococci may be isolated directly from 

 inflamed areas and from pus upon agar plates, better upon dextrose 

 agar plates. The colonies are minute, gray and transparent, and 

 may be readily overlooked; if they occur in association with staphy- 

 lococci or other rapidly growin'g organisms, they are readily over- 

 grown. The more virulent varieties develop less readily, and require 

 the addition of blood or ascitic fluid to ordinary media for their initial 

 growth outside the body. On blood agar plates (one part human blood, 

 two parts of nutrient, sugar-free agar) the majority of virulent strep- 

 tococci produce a wide, clear zone of hemolysis 4 to 8 mm. in diameter 

 around each colony. This medium is particularly valuable for the 

 isolation of streptococci. 3 On Loffler's blood serum growth is mod- 

 erately luxuriant; typical chains are found in the condensation water 

 of solid media, but not as a rule upon the surface. The organisms 

 grow feebly in gelatin stab cultures producing a few small discrete 

 gray colonies along the line of inoculation. Little or no growth is 

 found on the surface of the medium. Liquefaction does not take place. 



A slightly alkaline reaction (neutral to phenolphthalein) is most 

 favorable for the growth of streptococci; the addition of sugars, par- 

 ticularly dextrose, to ordinary media (but not blood agar) increases 

 the rate and extent of development, which, however, are soon limited 

 by the accumulation of acid products of fermentation. The addition 



1 Jour. Med. Research, 1901, vi, 163. 



2 Jour. Am. Med. Assn.,' 1913, Ixi, 727. 



3 Schottmiiller (Munch, med. Wchnschr., 1903, xx, 849) has classified streptococci 

 according to the changes they produce in blood agar as follows: 



I. Streptococcus longus pyogenes seu erysipelatis (Streptococcus pyogenes) produces a 

 wide, clear zone of hemolysis around the colony; in blood broth the color changes to a 

 burgundy red. Long-chained streptococci. 



II. Streptococcus mitior seu viridans (Streptococcus viridans) produces a greenish area 

 around the colony; a brownish color in blood broth. Short-chained streptococci. 



III. Streptococcus mucosus. No hemolysis on blood agar. Colonies viscid. Organisms 

 distinctly encapsulated. 



