178 INFLAMMATION AND SUPPURATION 



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. 55). 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 serum- 

 water-medium, in this respect differing from the pneumococcus. 

 It has a strong haBmoly tic action, as can be demonstrated by 

 growing it in blood-agar plates (p. 38). In bouillon, growth 

 forms numerous minute granules which afterwards 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 that those 

 which form the longest chains grow most distinctly in the form of 

 spherical granules, those forming short chains giving rise to a 

 finer deposit. To a variety which forms distinct spherules of 

 minute size the term streptococcus conglomeratus has been given. 



Varieties of Streptococci. Formerly the streptococcus pyogenes 

 and the streptococcus erysipelatis were regarded as two distinct 

 species, and various points of difference between them were 

 given. Further study, and especially the results obtained by 

 modifying the virulence (p. 182), have shown that these dis- 

 tinctions cannot be maintained, and now practically all authorities 

 are agreed that the two organisms are one and the same, 

 erysipelas being produced when the streptococcus pyogenes of a 

 certain standard of virulence gains entrance to the lymphatics Of 

 the skin. Petruschky, moreover, showed conclusively by inocu- 

 lation that a streptococcus cultivated from pus could cause 

 erysipelas in the human subject. 



Streptococci have also been classified according to the length 

 of the chains. Thus there have been distinguished (a) strepto- 

 coccus longus y which occurs in long chains and is pathogenic to 

 rabbits and mice ; (l>) streptococcus brevis, which is common in 

 the mouth in normal conditions, and is usually non-pathogenic ; 

 and (c) streptococcus conglomeratus, so called from its forming in 

 bouillon minute granules composed of very long chains. It may 

 be stated that pathogenic streptococci obtained from the human 

 subject usually form fairly long chains on agar, whilst the short 



