94 BACTERIA IN DAILY LIFE 



the first time upon numerous intricate problems 

 connected with the sanitary aspects of public 

 water-supplies which constitutes not the least im- 

 portant of the many services rendered by bacteri- 

 ology to the public. Perhaps one of the most 

 striking of these may be considered the insight 

 which it has afforded into the value of various 

 processes of water-purification, furnishing us with 

 the most subtle and searching tests, surpassing 

 in delicacy those of the most refined chemical 

 methods. 



Thus for years the processes of sand-filtration, 

 as practised at waterworks in dealing with river 

 and other surface waters, were regarded by chemi- 

 cal experts as of but little or no value, because, 

 on chemical analysis, but little or no difference 

 was found to exist between the filtered and un- 

 filtered samples respectively. Water engineers 

 started this method of water treatment in London 

 as far back as the year 1839, with no other object 

 than the distribution of a water bright and clear 

 on delivery, but, unknown to themselves, they 

 were carrying out a system of water-purification 

 the nature and extent of which has been left to 

 the infant science of bacteriology to unravel and 

 reveal. 



It was in the year 1885 that Dr. Koch's new 

 bacteriological water-tests were introduced, and 



