CHAPTER XIII. 

 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. 47. — WolfhugePs 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, vol. vii., Third Memoir. 



233 



