QUALITATIVE BACTERIOLOGICAL ANALYSIS. 43 



fine films appear on the surface with granular contents ; after 

 forty-eight hours the films become converted into shallow cups 

 surrounded by a green fluorescence. Under a low power the 

 colonies appear to have a margin set with very fine rays, and in 

 the centre a membrane may be seen ; later the membrane 

 disappears, and as the liquefaction extends the fine rays are 

 replaced by a hazy granular appearance. The colonies in the 

 depth of the gelatine are circular or oval in shape, and by 

 transmitted light appear to have a greenish-brown tinge. 



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

 funnel, and the medium acquires a green colour. 



Agar-slope. A smooth white growth, the agar assumes a 

 green colour. 



Broth. There is a diffuse growth, a slight pellicle forms on 

 the surface and a thick deposit appears at the bottom of the 

 tube ; the broth acquires a green colour. 



Potato. A yellowish-brown growth. 



Glucose-gelatine. No gas formation. 



Nitrate-broth. After seven days incubation at 22 C., large 

 quantities of ammonia are produced. 



Milk. A clot is formed which is slowly digested, the whey 

 assumes a green colour. 



Peptone-water. No indol reaction is obtained. 



Litmus-whey. There is no formation of acid. The blue 

 colour is changed to green ; after seven days incubation the 

 medium has a faintly alkaline reaction. 



Microscopical Appearance. A very short bacillus, generally 

 found in pairs. It may form chains. No spores observed. It 

 does not stain with Gram's method, and is very motile. 



The above description gives the characteristics of the type of 

 this organism which is most commonly found in water. Varieties, 

 however, are frequently found which vary considerably from the 

 type; some liquefy the gelatine in forty-eight hours, others do not 

 produce this result until the expiration of fourteen days. The 

 optimum temperature is usually 20-25 C. ; many varieties will 

 not grow at 37 C. ; others grow well at the latter temperature 

 and produce a copious growth on agar. The oxygen require- 

 ments vary greatly. Sometimes liquefaction of gelatine takes 

 place rapidly in the form of a deep funnel ; at other times it is 



