EXAMINATION OF WATER 303 



The majority of the organisms from a polluted water 

 which grow at blood-heat will be found on subculturing 

 to be the colon bacillus. The presence of the B. coli com- 

 munis in small numbers can hardly be considered as good 

 evidence of sewage-pollution, but when it is found in large 

 numbers it is fair to conclude this to be the case. 



The colon bacillus is spoken of by Klein* ' as a certain 

 index of fsecal pollution.' The recent researches of Dr. A. 

 A. Kanthack, however, show that the colon bacillus is 

 much more widely distributed than was formerly supposed, 

 being found by him in pure water, saliva, dust, etc., so that 

 the generally prevailing idea that its presence necessarily 

 signifies excretal pollution is erroneous. The widespread 

 distribution of the B. coli communis has, however, long 

 been known to bacteriologists, and it is comparatively rare 

 to find it absent from waters of high degree of purity that 

 have been exposed to the air. 



The Isolation of the Typhoid Bacillus from Water. — In 

 waters that have been very copiously contaminated with 

 sewage there is no great difficulty in detecting the typhoid 

 or colon bacillus, if present ; but it is necessary to bear in 

 mind that usually, when drinking-water has suffered sewage- 

 pollution, the amount of the pollution is relatively very 

 minute when compared with the great bulk of the water- 

 supply. The contamination of water by sewage is, more- 

 over, in the majority of cases, of an intermittent nature. 



When such waters are examined, as large a quantity as 

 1 c.c. or more of the water may be 'plate-cultured,' and 

 even then it is easy to miss the colon bacillus, not to speak 

 of the typhoid bacillus. 



In order to isolate the B. typhosus suspected to be present 



in a sample of water, it is necessary to submit a large 



* The Twenty -third Annual Eeport of the Local Government Board 

 — Supplement containing the Medical Officer's Eeport, p. 67. 



