STREPTOCOCCUS PYOGENES. 



169 



coccus longus (vide infra). As division may take 

 place in many of the cocci in a chain at the same time, 

 the appearance of a chain of diplococci is often met with. 

 In young cultures the cocci are fairly uniform in size, but 

 after a time their size presents considerable variations, 

 many swelling up to twice their normal diameter. These 

 are to be regarded as involution forms. In its staining 

 reactions the streptococcus resembles the staphylococci 

 described, being readily coloured by Gram's method. 



Cultivation. In cultures outside the body the 

 streptococcus pyogenes grows much more slowly than the 

 staphylococci, and also dies out more readily, being in 

 every respect a more delicate organism. 



In peptone- gelatine a stab culture shows, about the 

 second day, a thin line which 

 in its subsequent growth is seen 

 to be formed of a row of minute 

 rounded colonies of whitish 

 colour, which are more clearly 

 separate at the lower part of 

 the puncture. They do not 

 usually exceed the size of a 

 small pin's head, this size being 

 reached about the fifth or sixth 

 day. The growth does not 

 spread on the surface and no 

 liquefaction of the medium 

 occurs. The colonies in gela- 

 tine plates have a corresponding 

 appearance, being minute spheri- 

 cal points of whitish colour. On 

 ., .1.1 FIG. 48. Culture of the 



the agar media, growth takes streptococcus pyogenes on an 

 place along the Stroke as a agar plate, showing numerous 

 collection of small Circular discs colonies three successive 

 r . . , strokes. Twenty-four hours' 



of semi -translucent appearance, gr0 wth. Natural size, 

 which show a great tendency to 



remain separate (Fig. 48). The separate colonies remain 

 small and do not usually exceed i mm. in diameter. 



