STREPTOCOCCUS PYOGENES 



211 



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 gelatin 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 may 

 be separate at the lower part of the 

 puncture. They do not usually ex- 

 ceed 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 lique- 

 faction of the medium occurs. The 

 colonies in gelatin plates have a cor- 

 responding appearance, being minute 

 spherical points of whitish colour. 

 A somewhat warm temperature is 

 necessary for growth ; even at 20 C. 

 some varieties do not grow. On the 

 agar media, growth takes place along 

 the stroke as a collection of small 

 circular discs of semi - translucent 

 appearance, which show a great 

 tendency to remain separate (Fig. 

 52). The separate colonies remain 

 small, rarely exceeding 1 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 visible growth 



takes place. In milk it produces a strongly acid reaction but no 

 clotting of the medium. It ferments lactose, saccharose, and 

 salicin (Andrewes and Horder) it produces no fermentation of 

 inulin in Hiss's serurn-water-medium, in this respect differing 

 from the pneumococcus. It has a strong haemolytic action, as 

 can be demonstrated by growing it in blood-agai plates (p. 43). 

 In bouillon, growth forms numerous minute granules which after- 

 wards fall to the bottom, the deposit, which is usually not very 

 abundant, having a sandy appearance. The appearance in broth, 

 however, presents variations which have been used as an aid to 

 distinguish different species of streptococci. It has been found 



FIG. 52. [Culture of the 

 streptococcus pyogenes on 

 an agar plate, showing 

 numerous colonies three 

 successive strokes. Twenty- 

 four hours' growth. Natu- 

 ral size. 



