76 Bacteria in Relation to Country Life 



The presence of large numbers of the colon bacillus 

 becomes thus a danger signal, an indication that it 

 may have been accompanied by the typhoid bacillus. 

 Hence, both the chemical and bacteriological methods 

 employed in the examination of drinking-water aim to 

 detect pollution and its extent, if possible. The best 

 results are secured when the two are combined and a 

 measure thereby secured of the probable addition of 

 sewage materials, on the one hand, and, on the other, 

 of sewage bacteria, some of which may be carriers of 

 disease. Of late years the bacteriological methods have 

 been the subject of much careful study and give promise 

 of becoming more widely apphcable in the sanitary 

 examination of drinking-water. 



