150 SUPPURATION AND ALLIED CONDITIONS. 



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 staphylo- 



cocci described. 



Cultivation. In cultures outside the 

 body the streptococcus pyogenes grows 

 much more slowly than the staphylo- 

 cocci, 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 

 FIG. 43. Stroke sixth day. The growth does not spread 



culture of the strepto- Qn th surface and no li que f a ction of the 

 coccus pyogenes on ? . 



sloped agar, showing medium occurs. I he colonies in gelatine 



numerous colonies, plates have a corresponding appearance, 



bdn mlnUte S P herlcal P lntS f Whltish 



taining numerous colour. On the agar media, growth 

 streptococci in a pure takes place along the stroke as a col- 



g o d wth n ' T Nauuml lection of sma11 circular discs of semi- 

 size, translucent appearance, which show a 

 great tendency to remain separate 

 (Fig. 43). The separate colonies remain small and 

 do not usually exceed i mm. in diameter. Cultures on 

 agar kept at the body temperature may often be found 

 to be dead after ten days. On potato^ as a rule, no 



