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taken as indicators (they are not the only two) of
the amount of animal contamination. The mean
amount of “organic carbon” in Thames water
during the year was 0.307 parrs per 100,000, which
quantity was reduced to 0.207 by tbe West Middlesex
Company, and to 0.202 by the Grand
Junction Company. The average amount of “organic
nitrogen” present in Thames water was 0.051
parts per 100,000, reduced to 0.024 by both companies.
The Thames water contained 0.011 parts
per 100,000 of ammonia, usually due to decomposed
organic matter, which was entirely removed by both
companies. Of “nitrogen as nitrates and nitrites,”
the unfiltered water contained an average amount
of 0.217 parts per 100,000, which after filtration
was reduced to 0.216 by the West Middlesex, but
increased to 0.226 by the Grand Junction Company.
The examination of water by bacteriology is of
recent introduction, and the results obtained have
yet to be interpreted. The ever accumulating evidence
of infection being conveyed in drinking water
enhances the value of such examination, in view of
the acknowledged connection between micro-organisms
and disease. The samples of water for this
examination are taken immediately after the water
leaves a filter-bed, and by this means it is possible to
say that the filtered water at that point is (more
or less) sterile, and in certain cases to determine
whether each filter-bed is doing its work efficiently.