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 

 rule they are non-pathogenic. 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 

 of bacteria in water is very simple, and can generally be 

 prosecuted without much apparatus. The principle de- 



FlG. 40. Wolf hiigel's apparatus for counting colonies of bacteria upon plates. 



pends upon the equal distribution of a given quantity of 

 the water to be examined through a sterile liquid medium, 

 and the subsequent solidification of this medium in a 



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