136 BACTERIOLOGICAL EXAMINATION OF WATER. 



Potato-cultures. In two days a good yellowish-white growth, 

 which projects from the surface. 



Milk. In about four days the milk is coagulated, and gives 

 a strong acid reaction. 



Broth. The broth becomes very cloudy in two days. In ten 

 to fourteen days considerable whitish precipitate is produced. 

 A slight skin forms on the surface, but falls to the bottom on 

 shaking the tube. After some time two to three weeks the 

 broth is still cloudy. 



Nitrate-broth. Reduces nitrates in broth vigorously. 



Microscopical Characters. Short, plump, oval bacilli, with well- 

 rounded ends. No spore formation observed. Quite variable in 

 size ; slightly longer and thicker on potato than on agar. They 

 are frequently grouped in pairs. About 0'8 u to 1*9 /u long, 0'7 a 

 to 1 IUL broad. Very motile. Grow better at 37 C. than at 21 to 

 23 C. Require oxygen ; grow very scantily under a mica plate. 



Bacillus Superficialis. 



Found frequently in Lawrence sewage. 



Plate-cultures. The colonies become plainly visible to the 

 naked eye in about two days. Under a low power the colony 

 itself is seen to be approximately round, but is divided by irre- 

 gular lines into angular lumps, giving a somewhat cracked 

 appearance to the whole colony. On coming to the surface a 

 regular, round, homogeneous, finely granular expansion is 

 formed. To the naked eye the whole colony then appears as a 

 projecting translucent drop. The colony grows slowly, and 

 gradually liquefies the gelatine. When the liquefaction has pro- 

 ceeded for several days the colony has a yellowish-brown opaque 

 centre and a translucent edge. 



Gelatine-tubes. A very slow growth, taking about ten days 

 to liquefy the gelatine to the walls of the tube. The growth is 

 almost wholly on the surface, and there is only the scantiest 

 growth along the inoculation line. Even after standing for 

 several weeks only the gelatine in the upper part of the test 

 tube is affected by the growth. 



Agar -tubes. On agar there is a moist, lustrous, grey, trans- 

 lucent growth. After several weeks the growth is still smooth 

 and shiny and has assumed a light brown tint. 



