70 BACTERIOLOGICAL EXAMINATION OF WATER. 



in masses, and does not form spores. The colonies are round 

 with a bluish colour and slowly liquefy gelatine. In gelatine- 

 stab the medium is slowly liquefied in a funnel form. On agar 

 it forms a bluish growth. On potato there is a beautiful dark- 

 blue expansion. 



B. Cosruleus (Voges). 



Described by Voges. It is a small motile bacillus which is 

 decolourised by Gram. It has one polar flagellum, and does 

 not form spores. It will grow at 37 C., and form pigment. 

 The colonies in the depth are small ; on the surface they grow 

 out and have a typhoid-like form ; later, they become greyish- 

 blue and slowly liquefy the gelatine. In gelatine-stab it grows 

 slowly, and there is no pigment along the stab. In broth a 

 pellicle is formed, and a grey colour appears in the medium. 

 On agar there is a grey-coloured growth. Milk is not coagu- 

 lated ; the creamy layer has a sky-blue colour. On potato there 

 is a greyish-blue growth, which later becomes dark blue in colour. 



B. Indigoferus (Voges). 



Found in the Kiel water supply. It is a small motile bacillus, 

 which does not form spores. It is not coloured by Gram. 

 There is a slight growth at 37 C., but no pigment is produced 

 at this temperature. The colonies in the depth are small ; on 

 the surface, they grow out, are iridescent, and have a distinct 

 blue colour. In gelatine-stab there is a marked blue growth on 

 the surface, but no colour is formed in the stab ; the gelatine is 

 not liquefied. In broth there is a thin pellicle of a blue colour. 

 Milk is unchanged ; it has a bluish-grey colour on the surface. 

 On agar there is a beautiful dark-blue layer. On potato there 

 is a greenish-blue expansion, looking like a layer of caviar. 



B. Indigonaceus (Schneider). 



Found by Cliiessen in Spree water. It closely resembles the 

 B. indigoferus. The growth is, however, somewhat quicker. 

 In broth there is no pellicle. On potato the growth is deep 

 indigo blue when the medium is acid, and dark green when it is 

 alkaline. 



