146 MICRO-ORGANISMS AND DISEASE [chap. 



are distinctly arranged as a series of dumb-bells, in others 

 there is no such distinct arrangement. 



Streptococcus pyogenes forms in nutrient gelatine at 20° C. 

 already after twenty-four to thirty-six hours minute, dot-like, 

 grey, translucent, round colonies, which after two to three 

 days' growth are large enough to show under a magnifying 

 glass a darker, thicker centre and a thin, rounded, translucent 

 periphery ; after about a week or two the outline becomes 

 irregular, to one side more than to the other, thus forming 

 a more or less fan- or fern-shaped patch. It does not Hquefy 

 the gelatine. In streak culture on solid gelatine, blood-serum, 

 or Agar, the line of inoculation becomes marked as a 

 line of separate, rounded, translucent, or more or less whitish- 

 grey colonies, which as a rule, unless very thickly sown, do 

 not coalesce. In fluids — broth, condensation fluid of Agar or 

 of serum — the growth causes slight turbidity of the fluid and 

 is more in the form of stringy, flaky masses, these being 

 composed of continuous long chains much interwoven. On 

 potato the growth is not visible. Streptococcus pyogenes 

 as obtained from acute phlegmon, from chronic purulent 

 matter, from purulent and serous exudations of the viscera 

 and cavities, does not constitute a single variety, but 

 belongs to varieties differing from one another slightly 

 in the size of the cocci, in the rapidity of the growth 

 on gelatine, and in the length of the chains. Similarly 

 varieties of streptococci are known to occur in the 

 various normal secretions — fauces, brotichi, intestinal con- 

 tents, soil, &c. — which in some or all the above respects more 

 or less resemble the streptococcus pyogenes. The strepto- 

 coccus pyogenes cultivated from pus shows on inoculation 

 of a rabbit or mouse in many instances a tendency to form 

 inflammation and abscess ; in some instances, particularly 

 on injecting large doses, general acute septicaemic infection 



