BACTERIOLOGICAL EXAMINATION 221 



as these disease germs do than will any chemical com- 

 pounds. In the second place, the bacteriological 

 methods are superior in delicacy to any others. Klein 

 and Houston (1898) showed by experiment with dilu- 

 tions of sewage that the colon test was from ten to one 

 hundred times as sensitive as the methods of chemical 

 analysis; and studies of the self -purification of streams 

 have confirmed their results on a practical scale. Thus 

 in the Sudbury River it was found that while chem- 

 ical evidences of pollution persisted for 6 miles beyond 

 the point of entrance, the bacteria introduced could 

 be detected for 4 miles further (Woodman, Winslow, 

 and Hansen, 1902). 



The statement is sometimes made that while bac- 

 teriological methods may be more dehcate for the 

 detection of pollution in surface-waters, contamination 

 in ground-waters may best be discovered by the chemical 

 analysis. That such is not the case has been well 

 shown by Whipple (Whipple, 1903) who cites the fol- 

 lowing two instances in which the presumptive test 

 revealed contamination not shown by the chemical 

 analysis : 



" A certain driven- well station was located in swampy 

 land along the shores of a stream, and the tops of the 

 wells were so placed that they were occasionally flooded 

 at times of high water. The water in the stream was 

 objectionable from the sanitary standpoint. The wells 

 themselves were more than 100 feet deep; they pene- 

 trated a clay bed and yielded what may be termed arte- 

 sian water. Tests for the presence of Bacillus coli had 

 invariably given negative results, as might be naturally 



