198 VETERINARY BACTERIOLOGY 



coccus about 1 ^ in diameter, occurring in chains of greater or less 

 length. Sometimes there is a tendency toward diplococcus 

 formation, and the threads may be made up of many such diplo- 

 cocci. Where two organisms approximate, they are more or less 

 flattened. The organism is non-motile, does not produce spores, 

 is easily stained by the common anilin dyes, and is gram-positive. 

 The length and character of the chains is variable in different 

 media and under varying growth conditions, and likewise in strains 

 isolated from different sources. This latter fact has been made use 

 of by some investigators in an effort to perfect a classification. 



Fig. 85. Streptococcus pyogenes in lactose broth (Heinemann in " Journal of 

 Infectious Diseases"). 



The typical form does not produce capsules, although capsulated 

 varieties have been described. 



Isolation and Culture. The organism may frequently be 

 isolated in pure culture directly from the wound, but it is 

 generally necessary to pour plates and isolate from the colonies. 

 Care must be used in this latter method not to overlook the 

 colonies, for many strains produce minute colonies only, and 

 in mixed infections they may be missed. Inasmuch as most 

 strains ferment lactose, with the production of acid, the use of 



