1 86 INFLAMMATORY AND SUPPURATIVE CONDITIONS. 



remain small, rarely exceeding i 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 bouillon, growth forms numerous minute gran- 

 ules 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 strep- 

 tococci. 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. The question as to 

 the existence of varieties of streptococcus pyogenes will be dis- 

 cussed below. 



Bacillus coli communis. The microscopic and cultural characters are 

 described in the chapter on typhoid fever. The bacillus lactis aerogenes and 

 the bacillus pyogenes foetidus closely resemble it ; they are either varieties or 

 closely related species. The former is distinguished morphologically by its 

 general coccus or diplococcus form, and culturally by its growth on gelatin, 

 etc., by producing more abundant gas formation in sugar media and in acting 

 upon the starch of potato with gas production. In milk cultures its coagulative 

 action is more rapid, and usually in this medium exhibits encapsulation. In 

 gelatin its growth is more luxuriant and whiter than that of B. coli. 



Bacillus aerogenes capsulatus sometimes invades the tissues before death, 



and is characterised by the formation 



, f /^w^t* ' v of bubbles of gas in the infected parts. 



* *tr *i * ** V * ' * ts cnarac ters are described in Chap- 



^ ^',*% * terXVII. 



^Arf V H* *f ^wi * * Bacillus pyocyaneus. This or- 



T , <0 j, "** \ "* . ** * ganism occurs in the form of minute 

 ' '% ' * . **N f* rods i .5 to 3 /x in length and less than 



I ' ***. i* ,,5 u in thickness (Fig. 69). Occa- 



% j V O 7X 



t t . 4 ' .1 Vj% J sionally two or three are found at- 



* f " " ^* * - **/ tached end to end. They are actively 



***** **, > ** ?' motile, and do not form spores. They 



- ' % v 3> *^ ~ V stain readily with the ordinary basic 



\ * 1** If * stains, but are decolorised by Gram's 



'- V method. 



Cultivation, It grows readily on 



FIG. 69. -Bacillus pyocyaneus; young all the ordinary media at the room 

 culture on agar. . . ... 



Stained with weak carbol-fuchsin. x 1000. temperature, the cultures being distin- 

 guished by the formation of a greenish 

 pigment. In puncture cultures in peptone-gelatin a greyish line appears in 



