QUALITATIVE BACTERIOLOGICAL ANALYSIS. 103 



This is heated in the steam steriliser for half an hour, then 

 filtered and again sterilised. A litre of the suspected water is 

 taken arid 100 c.c. of this solution added to it, together with 

 0*5 c.c. of a 1 per cent, alcoholic solution of phenolphthalein, 

 and sufficient (about 2 to 3 c.c.) of a cold saturated solution of 

 sodium carbonate to render the mixture a permanent pink 

 colour. The mixture is divided into five or six Erlenmeyer 

 flasks and incubated at 37 C. At the same time sterile agar 

 plates are prepared and placed in the incubator with the flasks. 

 After twelve, sixteen, or twenty-four hours the fluid in one or 

 more of the flasks will be decolorised if the Colon bacillus be 

 present, and from the upper layer of the fluid a small loopful is 

 removed and rubbed over one of the sterile agar plates ; the 

 process is repeated for the other colourless flasks, the plates in- 

 cubated, and sub-cultures made from likely colonies. 



THE VALUE OF THE B. COLI COMMUNIS AS A SIGN OF SEWAGE 

 CONTAMINATION OF A WATER SUPPLY. 



The interpretation which is to be placed on the discovery of 

 B. coli in a water supply has been much debated. Kruse, in 

 1894, stated that the " Bacterium coli is in no way characteristic 

 of the faeces of men and animals. Such bacteria are found 

 everywhere in the air, in earth, and in water from the most 

 varied sources." Freudenreich and Miquel believe that B. coli 

 can be found in any water if a sufficient quantity is cultivated. 

 Levy and Bruns, however, considered that the B. coli found in 

 pure waters differed from the B. coli derived from faeces in the 

 absence of pathogenicity . The chief arguments, therefore, which 

 have been advanced against the acceptance of B. coli as an 

 indication of sewage contamination are as follows : (1) It 

 is abundant everywhere; (2) it multiplies readily outside the 

 animal body ; (3) it occurs in the excreta of mammals and 

 birds as well as in the intestine of man. If B. coli be abundant 

 everywhere, it is strange that Houston only found it in four out 

 of twenty-one samples of soil derived from different sources, viz., 

 from orchards, gardens, moorland, pasture, sand-pits, sea-shore, 

 fields, &c. It is true that nine of the samples yielded in phenol- 

 gelatine colonies which resembled those of B. coli ; but six of 

 these failed to respond to the gelatine shake-culture test, and 



