London's Pulse: Medical Officer of Health reports 1848-1972
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Hints from the Health Department. Leaflet from the archive of the Society of Medical Officers of Health. Credit: Wellcome Collection, London
Islington 1893
Thirty-eighth annual report on the health and sanitary condition of the Parish of St. Mary, Islington
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during the few hours which, in the absence of suitable arrangement at the works of the
different Companies, must necessarily elapse before the samples can be submitted to
cultivation in my laboratory. This is secured by immediately sealing, hermetically, the
glass tubes containing the samples and then packing them in ice. At the freezing point
of water, microbes either do not multiply at all, or do so with extreme slowness.
Although the collection of the samples for microbe cultivation from the filter-wells on
the works of the seven different Water Companies drawing their supplies from rivers
entails great additional labour, which can only be performed by an expert in bacteriology,
I am of opinion that it is the only trustworthy method by which the efficient filtration and
comparative bacterial purity of the Metropolitan waters can be ascertained.
NEW RIVER COMPANY.
Amount of storage 4•8 days.
Average thickness of sand on filters 1.8 foot.
Average rate of filtration per square foot per hour 2•3 gallons.
Maximum percentage of microbes removed 99•9
Minimum percentage of microbes removed 97•39
Average percentage of microbes removed 98•89
Table No. 7.—Microbe Determinations in the New River Company's Water.
| Source of Sample. | January. | February. | March. | April. | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Temp. C. | Microbes per c.c. | Temp. C. | Microbes per c.c. | Temp. C. | Microbe per c.c. | Temp C. | Microbes per c.c. | |||||||
| New River unfiltered water | o 4•0 | 31,421 | o 5•0 | 1,842 | o 7•6 | 500 | o 12•7 | 763 | ||||||
| New River Compy's supply | 3•1 | 30 | 6•0 | 32 | 7•0 | 12 | 12•4 | 6 | ||||||
| Source of Sample. | May. | June. | July. | August. | ||||||||||
| Temp. C. | Microbes per c.c. | Temp. C. | Microbes per c.c. | Temp. C. | Microbes per c.c. | Temp. C. | Microbes per c.c. | |||||||
| New River unfiltered water | o 15•8 | 1,973 | o 15•8 | 2,079 | o 17•0 | 3,934 | o 20•0 | 1,303 | ||||||
| New River Compy's supply | 17•2 | 12 | 18•4 | 35 | 17•5 | 37 | 19•3 | 34 | ||||||
| Source of Sample. | September. | October | November. | December. | Mean Microbes per c.c. | |||||||||
| Temp. C. | Microbes per c.c. | Temp. C. | Microbes per c c. | Temp C. | Microbes per c.c. | Temp. C. | Microbes per c.c. | |||||||
| New River unfiltered water | o 11•3 | 1,053 | o 11•7 | 2,276 | o 5•6 | 2,131 | o 5•4 | 3,408 | 2,867 | |||||
| New River Compy's supply | 12•6 | 10 | 12•7 | 30 | 5•5 | 23 | 5•7 | 22 | 24 | |||||
This table shows an excellent record. Throughout the year, there is not a single
sample which approaches nearer the limit of 100 microbes per c.c. than 37. In January
this Company reduced the number of microbes from 31,421 in the unfiltered water to 30 per
c.c. in the filtered water as pumped into the supply mains. Only one microbe in a
thousand survived the operation of filtration.