QUALITATIVE BACTERIOLOGICAL ANALYSIS. 57 



conical depressions in the gelatine, containing an irregular 

 white mass at the bottom. LTnder a low power the margin of 

 the colony shows threads of varying length passing off from the 

 periphery. In stab-gelatine the gelatine becomes cleft in the 

 form of an air-bubble, without any liquefaction ; sometimes, how- 

 ever, true liquefaction occurs. There is no growth on potato. 

 On agar there is a uniform grey expansion. It is a small, very 

 motile bacillus, which usually occurs singly or in pairs. It does 

 not form spores. It is not stained by Gram's method and grows 

 at 37 C. 



GROUP V. 



This group comprises a number of organisms which produce 

 a red pigment. The type of the group is the B. prodigiosus 

 of Ehrenberg, which is often found in waters from various 

 sources. 



B. Prodigiosus. 



The organism has the following characteristics : 



Colonies on Gelatine Plates. The colonies in the depth of the 

 gelatine are round or oval, sharply outlined, and of a clear red 

 colour. The surface colonies, after twenty-four hours, are seen 

 as round granular films, which at the end of forty-eight hours 

 appear as circular depressions with a red deposit in the centre. 

 Under a low power the colonies show a red granular centre, 

 surrounded by a circular clear zone and a narrow granular edge 

 at the periphery. 



Gelatine-stab. The gelatine is liquefied in the form of a 

 stocking and with a red coloured deposit at the bottom. 



A gar-slope. At first there is a colourless growth which 

 gradually acquires a red colour. 



Agdr-stab. In the line of inoculation the growth is colour- 

 less, but on the surface it has a red colour; the absence of colour 

 in the stab is due to the deficiency of oxygen. 



Potato. It forms a brilliant red growth. 



Milk. Red pigment is produced, and the milk is coagulated 

 through the simultaneous production of acid and lab-ferment. 



Broth. There is a diffuse growth with a red deposit. 



Glucose-gelatine. No gas formation. 



