CHAPTER X. 



THE SIGNIFICANCE AND APPLICABILITY OF THE 

 BACTERIOLOGICAL EXAMINATION. 



THE first attempt of the expert called in to pronounce 

 upon the character of a potable water should be to make 

 a thorough sanitary inspection of the pond, stream, well, 

 or spring from which it is derived. Study of the possible 

 sources of pollution on a watershed, of the direction and 

 velocity of currents above and below ground, of the char- 

 acter of soil and the liability to contamination by sur- 

 face-wash are conceded to yield evidence of the greatest 

 value. Often, however, an opinion is desired as to the 

 quality of water sent from a distance without the oppor- 

 tunity of examining its surroundings; and even when 

 sanitary inspection can be made, its results are by no 

 means conclusive. If house or barnyard drainage or 

 sewage is actually seen to enter a water used for drinking 

 purposes it is obviously unnecessary to carry out delicate 

 chemical or bacteriological tests to detect pollution. On 

 the other hand, no reconnoissance can show certainly 

 whether unpurified drainage from a cesspool does or does 

 not reach a given well; whether sewage discharged into 

 a lake does or does not find its way to a neighboring 



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