Streptococcus Pyogenes 319 



a frayed-out appearance around the edges, due to projecting chains 

 of the cocci. No hquef action of the gelatin occurs. 



Gelatin Ptinctures. — In gelatin puncture cultures no Uquefaction 

 is observed. The minute spheric colonies grow along the whole 

 length of the puncture and form a slightly opaque granular line. 



Agar-agar.^Upon agar-agar a delicate transparent growth de- 

 velops slowly along the line of inoculation. It consists of small 

 colorless, or slightly grayish transparent colonies which do not read- 

 ily coalesce. 



The addition of glycerin or of one per cent, of dextrose to the 

 agar-agar or other media greatly facilitates the growth of the cocci. 



On agar-agar plates the colonies are small grayish, translucent 

 and do not coalesce. If blood corpuscles be disseminated throughout 

 the medium the majority of virulent cocci cause hemolysis in a wide 

 zone about the colonies. 



Blood-serum. — The growth upon blood-serum and upon Loffler's 

 blood-serum mixture, resembles that upon agar-agar. The colonies 

 are small, white, discrete, and do not affect the medium. 



Potato. — The streptococcus does not seem to grow well upon 

 potato, the colonies being invisible. 



Bouillon.' — In bouillon the cocci develop slowly, seeming to prefer 

 a neutral or feebly alkaline reaction. The medium remains clear, 

 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 diffusely 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 in from three to five days because of the development of lactic 

 acid. 



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 4o°C., above 

 4o.s°C. the growth is slowed. The thermal death point is low. 

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



