CHAPTER XIII. 



BACTERIOLOGY OF WATER. 



UNLESS water has been specially sterilized, received and 

 kept in sterile vessels, it always contains some bacteria, the 

 number usually bearing a distinct relationship to the quan- 

 tity of organic matter present. 



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

 rule non-pathogenic. Wright,* in his examination 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. Pathogenic bacteria, 

 such as the spirillum of Asiatic cholera and the bacillus of 



Fig. 84. Wolfhiigel's apparatus for counting colonies of bacteria upon 



plates. 



typhoid fever, may occur in polluted water, but their occur- 

 rence is exceptional. 



The method of determining the number of bacteria in 

 water is very simple, and can be accomplished with very 

 little apparatus. The method depends upon the equal dis- 

 tribution of a measured quantity of the water to be exam- 

 ined in some sterile liquefied medium, whose subsequent 

 solidification in a thin layer permits the colonies to be 

 counted. 



The method originated with Koch, and may be performed 

 with plates, Petri dishes, or Esmarch rolls. It is always best 



* "Memoirs of the National Academy of Sciences," vol. vn, Third 

 Memoir. 



287 



