CHAPTER Xlll 

 BACTERIOLOGY OF WATER 



Unless water has been specially sterilized, and received and kept 

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

 usually bearing a distinct; relationship to the quantity of organic 

 matter present. 



The majority of the water bacteria are baciUi, and are as a rule 

 non-pathogenic. The bacteriological examination of water is directed 

 toward two objectives, first, the determination of the number of 

 bacteria in a given quantity of the water ; second, its purity or impurity 

 from the standpoint of sewage pollution and potability. A third 

 objective is sometimes added, namely, the demonstration of the 

 presence of the specific micro-organisms of typhoid and para-typhoid 

 fever, of dysentery and of cholera. The first two are' comparatively 

 easy to perform and are regularly carried out in many municipalities 



Fig. 79. — Wolfhugel's apparatus for counting colonies of bacteria upon plates. 



and water works; the third is so rarely successful that it is attempted 

 only under exceptional conditions. 



I. The Detennination of the Total Number of Bacteria in a Given 

 Sample of Water.— The method is very simple, and depends upon 

 the equal distribution of a measured quantity of the water to be 

 examined in some sterile hquefied medium, whose subsequent 

 soHdification in a thin layer permits the colonies to be counted, it 

 is, however, of the utmost importance that the water to be examined 

 shall be in every respect imchanged by manipulation and the occur- 

 rence of artificial conditions before the examinations are made. 



In the book upon "Standard Methods for the Examination of 

 Water and Sewage" pubhshed by the American PubUc Health 

 Association, Boston, i9r7, the best suggestions and methods can be 

 found, and from that work the majority of our recommendations 

 have been selected. 



The samples for bacterial analysis should be collected in bottles 



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