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(2.) Another microbe of common and copious occurrence in 

 sewage, and forming pale blue colonies on Drigalski medium > 

 is one of which the colonies appear rounded, uniformly raised, 

 and in two or three days show in reflected light a distinctly 

 greenish peripheral portion contrasting markedly with the 

 violet centre. The uniformly raised condition, the pale blue 

 colour, and the greenish margin are sufficiently distinct to 

 differentiate them from the typhoid or Gaertner colonies. 

 They are composed of short motile bacilli, and show no sign 

 of agglutination with typhoid blood serum. 



(3.) A further cylindrical motile microbe, forming deep blue 

 round colonies, is one which can be readily distinguished by 

 an ordinary gelatine sub-culture, for in this it forms here a 

 distinct bluish-green fluorescence, without liquefying the 

 gelatine, being, in fact, the common Bacillus fluorescens 

 putidus, viz., a microbe common in filth of all kinds.* 



(4.) One of the most frequent microbes botli of sewage and 

 of faecal matter, which forms round, bluish or blue-violet colonies, 

 raised in centre, flat at the periphery, and on inspection of the 

 Drigalski plates in some respects resembles the colonies of B. 

 typhosus or Gaertner, is one which is represented by short 

 cylindrical motile bacilli. On account of the blue colour of 

 the colonies with violet marginal part, on account of their 

 raised condition, and on account of their being made up of 

 cylindrical motile bacilli, they could be easily mistaken for B. 

 typhosus, the more so since they show distinct agglutination 

 with a highly potent typhoid serum, although in high dilution 

 no agglutination takes place. But the above characters pos- 

 sessed by the colonies as they appear on the Drigalski plate 

 might be presumptive of B. typhosus or B. Gaertner. More 

 careful observation and sub-cultures, however, soon show that 

 they are altogether different. In the first place, these blue 

 colonies are slower in their development, i.e., smaller than 

 those of B. typhosus or B. Gaertner. This difference is, how- 



* A microbe frequently met with in Drigalski plates infected with 

 eewage, forming bright blue colonies, is conspicuous by its forming rounded, 

 very flat, dry, scaly colonies ; it need not trouble us here in our diagnosis of 

 faecal microbes specific or non-specific. 



