QUALITATIVE BACTERIOLOGICAL ANALYSIS. 51 



B. megaterium. They have many points in common, and 

 varieties which seem intermediate between the various members 

 of the group are constantly isolated from water supplies. It 

 therefore appears best to place all these bacilli in one large 

 group. 



B. Mesentericus Vulgatus. 



This micro-organism has the following cultural characteristics : 



Colonies on Gelatine Plates. At the end of twenty-four hours 

 the colonies develop on the surface as small opaque white spots, 

 which at the end of forty-eight to seventy-two hours appear 

 sunk in small cups of liquefied gelatine. Examined at this stage 

 under a low power an opaque membrane is seen in the centre 

 surrounded by a clear circular zone ; the periphery of the colony, 

 outside the clear zone, is set with fine rays running out into the 

 gelatine. Sometimes this peripheral zone of hairs is not seen. 



Stab-gelatine. The gelatine is liquefied in the form of a 

 funnel. 



Glucose-gelatine (shake). No gas formation. 



Agar-slope. A thin, white, dry wrinkled growth. 



Potato. A thick white growth which becomes wrinkled and 

 furrowed. 



Peptone-water. No indol reaction obtained. 



Broth. There is at first a diffuse growth ; later, a wrinkled 

 pellicle appears on the surface and the broth clears below it. 



Nitrate-broth. Nitrates are reduced to nitrites. 



Milk. At 37 C. milk is coagulated ; the casein is digested 

 after several days incubation. 



Litmus-whey. After seven days incubation, the blue colour 

 disappears and the medium is rendered faintly alkaline. 



Microscopical Appearance. A small motile bacillus with 

 rounded ends. It forms short ellipsoidal spores. This bacillus 

 is smaller than the hay bacillus, but often has the same waggling 

 movement. It is stained by Grain's method. 



B. Mesentericus Fuscus. 



This bacillus resembles the vulgatus in most of its cultures. 

 The growths on agar and potato, however, are thinner and have 



