CHAPTER XII. 

 BACTERIOLOGIC EXAMINATION OF WATER. 



UNLESS water has been specially sterilized or distilled 

 and received and kept in sterile vessels, it always con- 

 tains some bacteria. The number will bear a very dis- 

 tinct relation to the amount of organic matter in the 

 water, though experiment has shown that certain patho- 

 genic and non-pathogenic bacteria can remain vital in 

 perfectly pure distilled water for a considerable length of 

 time. Ultimately, owing to the lack of nutriment, they 

 undergo a granular degeneration. 



The majority of the water-bacteria are bacilli, and as a 



FIG. 46. Wolf hiigel's apparatus for counting colonies of bacteria upon plates. 



rule they are non-pathogenic. Wright, 1 in his examina- 

 tion of the bacteria of the water from the Schuylkill 

 River, found two species of micrococci, two species of 

 cladothrices, and forty-six species and two varieties of 

 bacilli. Of course, at times the most virulent forms of 

 pathogenic bacteria those of cholera and typhoid fever 

 occur in polluted water, but this is the exception, not 

 the rule. 



The method of determining quantitatively the number 



1 Memoirs of the National Academy of Sciences, Third Memoir. 



169 



