576 A MANUAL OF BACTERIOLOGY 



removed by filtration through canvas bags, very con- 

 siderable purification is effected. 1 



Houston has introduced an " excess lime " method. 

 Enough lime is added to the water to render it decidedly 

 alkaline and germicidal for the colon bacillus in five to 

 twenty-four hours (for raw Thames water, about 1 of lime 

 in 5000 of water). At the end of this period a sufficiency 

 of pure stored water is added so as to precipitate the 

 excess of lime. With Thames water, 3 parts of raw water 

 with 1 part of stored water would be the approximate 

 quantities. 



The Tables on pp. 577 and 578 illustrate the influence 

 of storage and of sand filtration on the bacterial content 

 of a water. 



The Bacteriological Examination of Water 2 



The bacteriological analysis of water affords valuable 

 indications as to the purity or otherwise of a water, and, 

 if properly carried out, will indicate a pollution so small 

 in amount as to be incapable of detection by chemical 

 methods. 



The specimen of water should be collected in clean bottles 

 of about 100-200 c.c. capacity, sterilised preferably by 

 heat. If, however, the bottles be thoroughly cleaned and 

 rinsed out with a little strong sulphuric acid, and then 

 thoroughly rinsed several times with the water to be 

 examined before taking the specimen, no error will be 

 introduced. The stopper of the bottle should be tied 

 down with a thin layer of cotton-wool enclosed between 



1 Nankivell, Journ. of Hyg., xi, 1911, p. 246 ; Hewlett and Nankivell, 

 Rep. Med. Off. Loc. Gov. for 1911-12, p. 350. 



2 See Savage, Bacteriological Examination of Water Supplies (Lewis, 

 1906) ; Thresh, Examination of Water and Water Supplies (Churchill, 

 Ed. 2, 1913) ; Houston, Gordon and others in Reps. Med. Off. Loc. Gov. 

 Board, 1899-1904 ; Houston, Reports to the Metropolitan Water Board 

 and Studies in Water Supply (Macmillan & Co., 1913). 



