QUALITATIVE BACTERIOLOGICAL ANALYSIS. 89 



oval in shape and dark-brown in colour. On the surface after 

 twenty-four to forty-eight hours they appear as thin bluish- 

 grey transparent films with an irregular margin. Under a low 

 power they sometimes resemble flakes of glass with faint surface 

 markings, but more commonly they appear somewhat opaque 

 with a faint yellowish-brown colour, and show tracings of 

 ridges and depressions running from the centre to the peri- 

 phery ; at times wavy lines parallel to the margin are seen. 

 The gelatine is not liquefied. 



Gelatine-stab. On the surface an expansion appears like the 

 surface colonies just described, only whiter and thicker ; along 

 the stab there is a white growth. 



Gelatine-streak. A broad white growth with a crenate margin. 



Agar. A thick white growth, not characteristic. 



Potato. As a rule a thick brownish-yellow layer is produced ; 

 occasionally the growth is an almost transparent film like that 

 of B. typhosus. 



Mill:. Generally coagulated after twenty-four to forty-eight 

 hours incubation at 37 C. 



Litmus-wliey . Rendered acid ; after seven days incubation at 

 37 C., the amount of acid produced varies extremely, it always 



requires more than 6 per cent. ^ alkali and usually from 20 to 



40 per cent, of ^ alkali is required, to neutralise it. 



Glucose-gelatine "shake" (22 C.)l Abundant gas formation 



Glucose-agar-stab (37 C.) J in 24 hours. 



Witters Peptone and Salt solution. After 7 days incubation at 

 37 C. indol reaction is given on the addition of 1 c.c. of 

 potassium nitrite solution (0'02 per cent.) and a few drops of 

 pure sulphuric acid ; very often the reaction is obtained after 

 48 hours incubation. 



Broth. Rendered turbid in 24 hours at 37 C. ; later, a slight 

 film usually forms on the surface. 



Neutral-red Glucose-agar. Red colour changed to yellow and 

 greenish fluorescence produced. 



Nitrate-broth (O'l % KNO 3 , 5 % broth). Nitrates reduced to 

 nitrites. 



Gelatine (25 % at 37 C.). A distinct thick white film appears 

 on the surface. 



