Hygiene of water and water supplies / by Patrick Hehir.

Date:
1890
Catalogue details

Licence: Public Domain Mark

Credit: Hygiene of water and water supplies / by Patrick Hehir. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    water witTi fewer sucli germs. This may explain, in a manner, the discrepancy existing between the different opinions on the subject—the immunity in some and the susceptibiHty of other waters to pro- duce specific diseases. One point comes out promi- nently in the foregoing statements, and that is, that the most dangerous impurities of water are not those -that are visible : the potent agencies in the produc- tion of diseases from water are germs, and these from their minuteness cannot be determinedby any known chemical tests. A knowledge of the method of conducting a microscopical examination of water is then a matter of the greatest importance to those who have to decide as to the potability of water. In making an ordinary microscopical examination of water, we place a drop of the water on a cover glass, and allow it to evaporate (preferably under a bell glass). This may be examined at once, or passed through a flame.three or four times, and then stained with one of various aniline pigments. The microscopical examination of water before and after filtration is of some importance, and the result is well shown in the analysis given in the Appendix. When a water is much discolored from impurities, there is no difficulty in obtaining enough of the sedimentary matter for microscopical examination. But sometimes the sediment is so smallm amount that several sHdes may have to be examined before anything is met with. When this is the case, a long narrow cylindrical glass, thoroughly cleaned, should be filled with the water to be examined, allowed to stand for 24 hours, and then the water to within