EXAMINATION OF WATER 



393 



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 colon bacillus was formerly 

 regarded as a certain index of. faecal 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 bacteri- 

 ologists, and it is comparatively rare to find it absent from 

 waters of high degree of purity that have been exposed to 

 the air. The presence of the B. coli coynmunis 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. 



