Bacteriological survey of "surface" water supplies.

Date:
[between 1890 and 1899]
Catalogue details

Licence: Public Domain Mark

Credit: Bacteriological survey of "surface" water supplies. Source: Wellcome Collection.

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

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    Mace (1S97), after explaining that the mere number of bacteria must be taken only as an indication and not as affording an absolute criterion, gives the following scale of purity :— Very pure water o to 10 bacteria to the cubic centimetre. Very good ,, ... ... 20 to 100 ,, >» Good ,, ... ... 100 to 200 ,, »> Passable (mediocre) water... 200 to 500 ,, n Bad water ... ... ... 500 to 1,000 „ >> Very bad water ... ... 1,000 to 10,000 and over ,, „ Migula (1890) argues that the mere number of the colonies affords us no means of judging of the fitness of water for drinking purposes, but that, on the other hand, a great deal depends on the number of kinds present. Good pure spring water from mountains contains only a few species ; water which has been contaminated by drainage contains, on the con- trary, an exceedingly great number of species. Migula holds that there should never be more than ten different species of bacteria in good drinking water. He qualifies this statement by saying that a water containing fewer species may have to be con- demned on account of the nature of the bacteria, whilst sometimes a water containing more than ten kinds may be considered fit for drinking purposes. As regards the number of colonies, Migula is inclined to admit a maximum limit of 500, i.e., the limit admitted by most observers. For a time bacteriologists attached a considerable importance to the presence or absence of liquefying bacteria, but I think that as there are several rapidly liquefying bacteria often present, even in unpolluted water, it is necessary to distinguish between those liquefying bacteria which are associated with pollution and those which are not, if the presence of liquefying bacteria is to be used as a criterion at all. Meade-Bolton, Lustig, G. Roux, all well known in connection with the bacteriological examination of water, have expressed views similar to but less categorical than those just quoted. I need not say more to show that there is, as yet, no consensus of opinion among bacteriologists with regard to the interpretation of the results of water analysis. There is, however, a general tendency to admit that much judgment has to be used in interpreting these results. There is no difficulty with regard to very bad waters. Those who propound numerical standards all agree that a water containing 1,000 germs is not good. This in itself is already a very important point gained, for in many suspicious or bad waters which might chemically appear good, the presence of organic impurities can easily be detected in this way. But when we have to deal with waters containing less than 1,000 bacteria to the cubic centimetre, there is a considerable divergence in the views expressed by various write!?!!