PURIFICATION OF WATER FOR DRINKING PURPOSES 147 



tion of the water. Chemically no difference could be 

 detected, but bacterially the unfiltered water inFebruary, 

 March and April exhibited an abnormally large number 

 of micro-organisms, causing the average for the year to 

 rise from 123 in 1890 to, 583 in 1891 per c.c. On the 

 other hand, so excellent was the working of the filters 

 that the filtrate was totally unaffected ; the average for 

 the filtered water in 1890 being 24, and in 1891 23 

 micro-organisms per c.c. 



The report goes on further to state that, whilst in 

 the year 1880, when the lake was frozen, an epidemic 

 of diarrhoea and typhoid fever which occurred was attri- 

 buted to the water-supply, in 1891, in spite of the long 

 duration of the ice on the lake, the public health in 

 these respects was not only normal, but if anything 

 more satisfactory than usual. It has also been satis- 

 factorily proved, says the report, by careful exami- 

 nation of statistics, that since the establishment of 

 the new filtration-works in 1886 a very marked dimi- 

 nution has taken place in the number of cases of 

 typhoid. 



So far we have only had under consideration in- 

 stances in which sand-filtration has been so efficiently 

 carried out that the results are eminently, satisfactory. 

 But it must not be imagined that this is invariably the 

 case, and the following instances are given- to illustrate 

 how dependent are the results obtained upon the care 

 with which the process is conducted. 



Konigsherg Water-supply. — Konigsberg ^ is supplied 

 with water from springs, streams and wells. The main 

 supply is obtained at some distance from the town, in 



^ ' Bericht iiber die bakteriologische Untersuchung des Konigsberger 

 Wasserleitungswasser in der Zeit von December 1890 bis December 1891/ 

 Laser. Centralhlatt filr allgemeine Gesundheitsjpflege, 1892, p. 133. 



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