QUANTITATIVE BACTERIOLOGICAL ANALYSIS. 41 



(Fuller, 1899) records 27,200 organisms per c.c. in the 

 water of the Ohio River between September 21, 1898, and 

 January 25, 1899, while the average content of the effluent 

 from the Jewell filter was 400. In well-managed purifi- 

 cation plants the bacteria in the effluent are determined 

 daily, and any deviation from the normal value at once 

 reveals disturbing factors which may impair the efficiency 

 of the process. In Prussia official regulations demand 

 such systematic examinations and prescribe 50 as the 

 maximum number of bacteria allowable in the filtered 

 water. In the same way the condition of an unpurified 

 surface supply may be determined by daily bacteriological 

 analyses and warnings of danger issued to the public, as 

 has been done at Chicago and other cities. In general, 

 any such regular determination of variations from a nor- 

 mal standard furnish ideal conditions for the bacteriolog- 

 ical methods; and the detection by Shuttle worth (Shuttle- 

 worth, 1895) of a break in a conduit under Lake Ontario 

 by a rise in the bacteria of the Toronto water-supply may 

 be cited as a classic example of its application. 



Often, however, the expert is called to pass upon the char- 

 acter of a water of which no series of analyses is available 

 and whose surroundings it may be impossible for him to in- 

 spect. It has been said that single bacteriological analyses 

 of this kind are valueless; but this we believe cannot always 

 be maintained. Knowing the normal bacterial range 

 for a given class of waters, even an isolated analysis may 

 show such an excess as to have great significance, as a 

 few practical examples may make clear (Winslow, 1901). 



