CHAPTER II 



BACTERIA IN WATER 



IN entering upon a consideration of such a common article 

 of use as water, we shall do well to describe in some 

 detail the process by which we systematically investigate the 

 bacteriology of a water, or, indeed, of any similar fluid sus- 

 pected of bacterial pollution. 



The collection of samples, though it appears simple 

 enough, is sometimes a difficult and responsible under- 

 taking. Complicated apparatus is rarely necessary, and 

 fallacies will generally be avoided by observing two direc- 

 tions. In the first place, the sample should be chosen as 

 representative as possible of the real substance or conditions 

 we wish to examine. Some authorities advise that it is 

 necessary to allow the tap to run for some minutes pre- 

 vious to collecting the sample; but if we desire to examine 

 for lead chemically or for micro-organisms in the pipes 

 biologically, then such a proceeding would be injudicious,^ 

 Hence 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 bacteriological cleanliness in 

 all our manipulations. This means that we must use only 

 sterilised vessels or flasks for collecting the sample, and in 

 the manipulation required we must be extremely careful 



^ Water from a house cistern is rarely a fair sample. It should be taken 

 frtim the main. If taken from a stream or still water, the collecting bottle 

 should be held about a foot below the surface before the stopper is removed. 



37 



