138 BACTERIOLOGICAL EXAMINATION OF WATER. 



Broth. The broth becomes slightly turbid and a heavy 

 white precipitate is formed. In several weeks a thick tenacious 

 skin forms on the surface ; the main body of the broth is then 

 clear. 



Nitrate-broth. No change in the nitrates after fifty days. 



Microscopical Characters. Large, long bacilli with well-rounded 

 ends. Often occur in pairs and short strings. Many of the 

 individual bacilli are slightly curved. No spore formation 

 observed. About 4 JJL long and 0*9 u broad. A slow, sluggish 

 movement. Grow better at 21 C. than at 37 C., and develop 

 very poorly under the mica plate. 



Bacillus Hyalinus. 



Isolated from the sand of Tank 13 at a time when the tank 

 was nitrifying well. Found in large numbers in the sand. 



Plate-cultures. Fast-growing. In twenty-four hours the 

 colonies can be plainly seen with the naked eye. In all, even 

 in the smaller colonies, there is a dark centre surrounded by 

 a broad translucent zone, which gives a hazy appearance to the 

 colonies. With a low power the interior is seen to be coarsely 

 fibril lar, with short fibrils radiating from the edge. In two 

 days the colonies are large about one and a half centimetres 

 in diameter ; the contour is evenly round, the interior slightly 

 translucent ; the rim is distinct, opaque, yellowish ; the edge 

 still shows radiating fibrils. 



Gelatine-tubes. In two days a long, narrow, funnel-shaped 

 growth. The gelatine is rapidly liquefied, and is at first cloudy, 

 with a precipitate at the bottom of the funnel. In about eight 

 days the tube has assumed a highly characteristic appearance : 

 a lustrous, tenacious, white scum, a slight, flocculent precipitate, 

 and perfectly transparent liquefied gelatine between. Grows 

 very well in acid gelatine. 



Agar-tubes. A rapid, dry, spreading, greyish growth. Dull, 

 tough, and rather thin. When about four days old warty pro- 

 jections appear. 



Potato-cultures. In two days the growth is just visible; in 

 four days good, spreading, whitish-grey growth. Later, small 

 protuberances appear on the surface. 



Milk. In seven days strongly coagulated, reaction acid. 



