54 BACTERIOLOGICAL EXAMINATION OF WATER. 



Milk. Unchanged . 



Broth. Diffuse growth ; a deposit forms at the bottom, and 

 later a pellicle appears on the surface. 



Nitrate-broth. Powerfully reduced to nitrites and ammonia. 



Potato. A moist, white growth. 



Litmus-whey. The reaction of the medium remains un- 

 changed. 



Microscopical Appearance. A large bacillus, with rounded 

 ends; forms oval spores. It is motile; movement sluggish. It 

 is stained by Gram's method. 



The B. megaterium (De Bary) is described with the sewage 

 organisms. 



The B. filiformis described by Tils also belongs to this group. 

 A culture of this organism produced colonies on gelatine exactly 

 resembling moulds. In stab-gelatine a beautiful tree-like growth 

 was obtained. On agar there was a thick growth with fibres 

 passing out from the margin. The growths in peptone- water, 

 broth and glucose-gelatine exactly resembled those of B. 

 mycoides. It formed long threads, and divided into segments, 

 each containing a spore. 



GROUP IV. 



This group contains a large number of bacilli which are very 

 common in unfiltered water supplies. It includes the B. lique- 

 faciens of Eisenberg, the B. liquefaciens of Lustig, the B. liquidus 

 of the Franklands, the B. punctatus of Zimmermann, the B. aqua- 

 tilis communis of Flligge, B. liquefaciens communis of Stern- 

 berg, c. The B. liquefaciens which occurs in unpolluted 

 waters has the following characteristics : 



Colonies on Gelatine Plates. The surface colonies appear in 

 twenty-four hours as small white points, which under a low 

 power have a regular margin and granular contents ; often there 

 is an appearance of convoluted threads passing from the centre 

 to the periphery. In forty-eight hours the colonies appear as 

 cup-shaped depressions, which rapidly extend; under a low 

 power the margin is now seen to be smooth, and each cup 

 contains flocculent masses made up of clumps of bacteria ; later 

 the margin of the colony often shows indistinctly marked 

 spinous processes. 



