114 BROOMALL : MUNICIPAL WATER SUPPLIES. 



and uniform in its results, both by reason of the larger quan- 

 tities dealt with as well as by reason of the intrinsic accuracy 

 of the methods. One reason for this accuracy is that the 

 chemical method is not aflfected by any sudden, unavoidable 

 focus of bacterial activity that may appear at any moment 

 and as suddenly and unavoidably vitiate the results of the 

 bacteriological determinations. To offset this, however, the 

 latter method has the quick and specific fermentation tube 

 test for directly indicating the presence of sewage contamina- 

 tion through the recognition of one of the prominent intestinal 

 bacteria, the Bacillus coli covivuinis . 



P'rom what has been said it is evident that neither the 

 chemical nor bacteriological method alone is sufficient for the 

 proper examination and study of a water supply. Routine 

 daily tests by both methods, using for instance, chemically, 

 nitrites and chlorides, and bacteriologically, colon}' counting 

 and the fermentation tube, are probably all the tests necessary' 

 to safeguard an existing water supply already found satisfac- 

 tory. Any unexplained abnormality in the reactions should 

 at once be met by a more thorough examination. As long as 

 things go uniformly along little need be feared. The tests 

 are so simple that any intelligent person can perform them in 

 routine work and the expert need onl}' be sent for when the 

 tests indicate danger. No community should be satisfied to 

 go ahead day after day using a given water without having 

 it methodically subjected to these simple routine tests. 



