38 



BACTERIA IN WATER 



Frankland has shown that the river Dee affords another example, 

 even more perfect, of pollution and restoration repeated several times 

 until the river becomes almost bacterially pure. 



Professor Boyce and his colleagues have recently made an 

 examination of the river Severn before and after its waters pass the 

 town of Shrewsbury.* Their findings may be represented briefly as 

 follows : — 



This table and that of Prausnitz — and many other workers have 

 produced similar records — illustrate the effect of (a) local pollution, 

 and (&) river purification, upon the bacterial content of water, to 

 which subsequent reference wili be made. The record respecting the 

 Severn includes also the indication of sewage pollution by the 

 presence of B. coli. An elaborate examination has also been made 

 of the water of the river Thames and the Thames estuary, by 

 Houston, and the report dealing with it is full of information on 

 the subject, to which reference should be made.f 



Lastly, the accompanying table (pp. 39 and 40), for 1902 and 1903, 

 deals with the London water supply as examined by Crookes and 

 Dewar. \ It is concerned, it should be added, only with numerical 

 results. 



This record, compiled from the monthly reports respecting the three 

 waters supplied to the metropolis, illustrates many interesting points 

 upon which we have not space to dwell fully. A few notes, however, 

 upon an actual example are more useful than much theoretical 

 information, and therefore a brief study of these figures may be made. 

 In the main the table illustrates two points more clearly than the 

 preceding tables. The first is the effect of filtration, and the second 

 is the effect of season, upon the number of bacteria in water. In 

 respect to the former, comment is needless. It is only necessary to 



* Royal Commission on Sexnaqe Disposal, Second Report, 1902, p. 99. 

 t Ihid., Fourth Report, 1904, vol. iii., pp. 1-75. 

 X Metropolitan Water Supply, 1902 and 1903. 



