Applied bacteriology : an introductory handbook .. / by T.H. Pearmain and C.G. Moor.

  • Pearmain, T. H.
Date:
1897
Catalogue details

Licence: Public Domain Mark

Credit: Applied bacteriology : an introductory handbook .. / by T.H. Pearmain and C.G. Moor. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

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    passed through the filter, and the filtrate was found to be sterile. Further investigation showed that this ceased to be the case when the filtration was continued for a few hours or less instead of a few minutes. It was found that in such case the filtrate contained the same organisms as the un- filtered water; and the sterility of the earlier filtrates was accordingly due to the circumstance that they had been examined before sufficient time had been allowed for the organisms to be washed through the filter. It was also found that the chemical matters arrested by the filter temporarily arrested a portion of the organisms, and served as a suitable culture-ground for such organisms, which survived and multiplied for considerable periods in the filter before being ultimately washed through. In consequence, the number of organisms became after a short time much larger in the filtrate than in the unfiltered water. Filters once polluted with the cholera or typhoid bacillus were also found to convey the bacillus to sterile water passed through them at considerable periods—up to six weeks or more— after pollution. This fact has been responsible for several epidemics, such as that of Lucknow in 1894, in which, out of 646 officers and men in the East Lancashire Kegiment, 143 were attacked by cholera, and 92 died. This epidemic was conclusively traced to the infection of the barrack-room filter by the cholera microbe. Sand-filtration.—The working of sand-filters on a large scale depends on the facts described above. A sand filter- bed consists of a layer of sand from 2 to 4 feet deep, supported on gravel. The fineness of the grains of sand, the depth of the filter, and the rate of filtration, all afifect the working of the filter in the removal of organisms. The coefficients given for safe working are filtration through a sand-layer not less than 80 centimetres thick, at a rate not exceeding 100 millimetres per hour, and giving a filtrate