112 THE PATHOGENIC BACTERIA. 



csemia and of many surgically common infections (Fig. 48 and 

 Plate I.). 



FIG. 48. 



s IV--"-- 



( V i 1 



"::.-' 



Streptococcus pyogenes. (Abbott.) 



Morphology. The streptococcus is a micrococcus varying 

 in size from J to 1 mikron in diameter, spherical in shape, 

 and arranged as a chain of variable length. When grown in 

 liquid media, this chain consists of from 30 to 40 elements, 

 but in solid media a chain usually consists of from 7 to 10 

 cocci. In young cultures the diameters of all the cocci of the 

 chain are equal ; in older cultures they vary very much even 

 in the same chain. 



Biologic Characters. The streptococcus is aerobic and fac- 

 ultative anaerobic. At 37 C. it clouds bouillon in twenty- 

 four hours, and this becomes again clear at the end of three 

 or four days, when small spherical bodies may be seen at the 

 bottom of the tube. The bouillon becomes acid. On gelatin 

 it forms small spherical opaque colonies about the size of a 

 pin-head, which cease to increase after the third or fourth 

 day. It does not liquefy gelatin. On agar-agar also it forms 

 spherical colonies of the size of a pin-head, semitransparent 

 and of a grayish- white appearance, shaped somewhat like a 

 bead. It does not develop on potato. The streptococcus does 

 not live longer than three weeks in cultures. When grown on a 

 medium containing red blood cells an area of haemolysis and 

 decolorization surrounds the colonies. This feature of growth 

 aids in differentiating them from pneumococci. It stains by 

 the Gram method, and also by the other anilin dyes. 



Pathogenesis. Intravenous inoculations in animals produce 



