96 BACTERIOLOGICAL EXAMINATION OF WATER. 



isodiametric, and porcelain white in colour ; the colonies in the 

 depth are yellowish, round, granular centres. In gelatine- 

 stab it grows well along the line of inoculation, and on the 

 surface forms a nail-head shaped expansion ; the gelatine is not 

 liquefied. On potato it produces white raised colonies, 

 permeated with gas bubbles, which often run together and form 

 a cream-like layer. It produces gas in sugar media, and 

 coagulates milk. 



Escherich does not mention the formation of indol ; but a 

 pure culture from Krai's laboratory, \vhich I examined, gave a 

 marked indol reaction in Witte's peptone. Microscopically it 

 appears as a non-motile short rod with rounded ends. The 

 most characteristic growth of this organism is the creamy 

 layer containing gas bubbles which appears on potato. The 

 cultures which I examined did not always show the convex 

 isodiametric colonies ; very often the surface colonies grew out 

 with a thin irregular margin like the typical B. coli. 



Bacillus Cavicida. This organism was isolated by Brieger 

 from faeces. Its colonies on gelatine plates are said to be very 

 characteristic, showing a white growth, with concentric rings, 

 like the arrangement of the scales on a tortoise-shell. On 

 potato it forms a yellow slimy layer, and in sugar media 

 produces propionic acid. It does not liquefy gelatine. Micro- 

 scopically it appears as short rods, which do not form spores. 

 A culture of this bacillus from Krai's laboratory produced 

 gas in glucose-gelatine shake, and traces of indol in peptone 

 solution. It did not, however, coagulate milk. It appeared 

 to correspond to one of the varieties of B. coli. 



Bacterium Tholoeideum was isolated by Gessner from the 

 intestinal canal of healthy men, and strongly resembles the 

 B. lactis aerogenes. In gelatine plates the surface colonies appear 

 as nail-headed, slimy, opaque growths ; later, they form large 

 expansions, lose their slimy character, and show a grey centre 

 surrounded by concentric rings. Under a lower power they are 

 circular, with a colourless, bright shining margin ; towards the 

 centre fine radiating brownish lines are seen. The deep 

 colonies are whetstone-shaped, of a yellowish-white colour. 

 Under a lo\v power they appear at first olive-green in colour ; 

 later, they become dark grey-green, and resemble date-stones in 



