CHAPTEE II 



BACTERIA IN WATER 



Quantity of Bacteria in Water — Quality of Water Bacteria : (a) Ordinary Water 

 Bacteria ; (6) Sewage Bacteria ; B. eoli communis ; (c) Pathogenic Bacteria in 

 Water — Interpretation of the Findings of Bacteriology — Natural Purification 

 of Water — Artificial Purification of Water — Sand Filtration — Domestic Puri- 

 fication of Water. 



The collection of samples, though it appears simple enough, is 

 sometimes a difficult and responsible undertaking. Complicated 

 apparatus is rarely necessary, and fallacies will generally be avoided 

 by observing two directions. In the first place, the sample should 

 be chosen as representative as possible of the real water or conditions 

 we wish to examine. Some authorities advise that it is necessary 

 to aUow the tap to run for some minutes previously to collecting 

 the sample; but if we desire to examine chemically for lead or 

 biologically for micro-organisms in the pipes, then such a proceeding 

 would be injudicious.* If it is well water that is to be examined, 

 the well should be pumped for some minutes before taking the 

 sample. If it is river water which is to be examined, it is important 

 to collect the sample without incorporating any deposit. In short, 

 we must use common sense in the selection and obtaining of a 

 sample, following this one guide, namely, to collect as nearly as 

 possible a sample of the exact water, the quality of which it is 

 desired to learn. In the second place, we must observe strict 



* Water from a house cistern is rarely a fair sample of a town supply. It 

 should be taken from the main. If taken from a stream or still water, the collect- 

 ing bottle should be held about a foot below the surface before the stopper is 

 removed. 



33 C 



