QUALITATIVE BACTERIOLOGICAL ANALYSIS. 155 



Bacillus Subtilis (Sewage variety B.). 



Isolated from crude sewage and effluents from coke-beds. 



Gelatine-plate Cultures. Rapidly forms greyish- white circles 

 of liquefied gelatine. The masses of bacteria lying in the 

 liquefied gelatine may present a rosette or star-shaped appear- 

 ance. The parallel arrangement of the bacilli at the periphery 

 of the colony is absent, or not so well marked as in the above 

 variety. A skin forms on the surface of the liquefied gelatine. 



Agar-streak. In twenty hours at 20 C. there is a greyish- 

 white layer. In forty-eight hours the growth is somewhat dry 

 and granular looking, and in four days ridges stand oat from 

 the surface of the medium about one-sixteenth of an inch. 

 They are usually arranged in more or less transverse folds. 



Gelatine-stab Cultures. Rapid liquefaction all the way down 

 the stab, but as the growth proceeds the liquefaction spreads 

 in a cylindrical fashion from above downwards. A distinct 

 skin forms on the surface, which eventually sinks in the 

 liquefied gelatine. 



Gelatine-silage. There is no gas formation. 



Broth. Diffuse cloudiness ; on the surface a skin forms, 

 which is brittle, and sinks on shaking the tube. 



Indol. There is no formation of indol. 



Litmus-milk. The pale-blue colour gradually fades, but no 

 clotting or redness occurs. In eight days the milk is almost 

 transparent, and of a pale, dirty yellow colour. 



Potato Cultures. A white rather dry-looking coat is formed. 

 Later, portions of the growth become upraised, and some- 

 times present a worm-like appearance. 



Microscopical Characters. Large, long bacillus with rounded 

 ends, often in long chains. It forms spores and has a 

 waddling, sluggish movement. It shows little or no growth 

 at 37 C., but grows luxuriantly at 20 C, 



Thermophylic Bacteria. 



The micro-organisms which are capable of growing luxuriantly 

 at a temperature of 60 to 70 C. are of considerable interest to 

 the water bacteriologist. They are found in the alimentary 

 canal of human beings and animals, in sewage, and in polluted 



