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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    of bacteria, but the number contained therein varies very much with the source of the water. In stagnant water, such as is found in brooks and small ponds, the number of micro-organisms present is always very great. The comparatively pure water of large lakes and upland streams often contains many bacteria, but these are always harm- less saprophytes, which find their normal habitat in such waters. Thus, in the purest upland streams and lakes we frequently find that the number of bacteria in 1 c.c. is under 100, while in town sewage are many millions in the same volume. In ordinary rivers the number is generally between 1,000 and 100,000 per c.c. In the case of waters from deep-seated springs, the presence of more than 100 organisms per c.c. is conclusive evidence that the water has undergone some contamination with surface-water. Micro-organisms are also found, although not in great numbers, in rain-water, hail, snow, and even in the ice of glaciers. The water-supplies of large towns come for the most part either from rivers or lakes, with supple- mentary supplies from wells. Many of these water-supplies under ordinary circumstances may be satisfactory, but there is always the danger of sewage-pollution. It must not be forgotten that all polluted waters have a natural tendency to purify themselves if exposed to the air. As regards the nature of the organisms found in natural waters, they are for the most part bacilli, micrococci being somewhat rare, while spirilla are not unfrequently found. About 240 species have already been discovered in water, the majority being harmless saprophytes, although many pathogenic species are also found. As has already been pointed out, typhoid and cholera are essentially water-borne diseases. In many of the recorded cases of water-borne typhoid and cholera, the amount of organic matter accompanying the specific pollution was so extremely small that the water-