The bacteriological examination of food and water / by William G. Savage.

  • Savage, William George, Sir, 1872-
Date:
1914
Catalogue details

Licence: In copyright

Credit: The bacteriological examination of food and water / by William G. Savage. Source: Wellcome Collection.

Provider: This material has been provided by London School of Hygiene & Tropical Medicine Library & Archives Service. The original may be consulted at London School of Hygiene & Tropical Medicine Library & Archives Service.

    69/196 (page 53)
    Deep well waters when uncontaminated contain but few bacilli and no B. coli or other indicator organisms. In waters of this class therefore a considerable increase in the number of organisms and in particular the presence of B. coli, with or with- out streptococci, must indicate pollution with surface water or other undesirable material and much higher standards of require- ments are reasonable. It is justifiable to maintain an attitude of great suspicion towards any water from such sources which contains B. coli in 100 c.c. or less. To ascertain the precise source of contamination and to measure and assess its danger often requires a very careful study of topographical and geological conditions and the making of a series of subsidiary bacteriological examinations. One important cause of bad bacteriological results from deep water supplies, which it is important to eliminate or confirm at the outset, is contamination of the supply at the surface outcrop. Frequently a spring runs some distance on the surface before it is collected and utilised, and samples taken at a point on the distribution side may entirely owe their bad bacteriological results to surface contamination of an otherwise pure deep water supply. It is important to realize how frequently such surface con- tamination occurs and is allowed to exist owing to the care- lessness or want of knowledge on the part of those entrusted with the care of the water supply. The following is a striking illustration of such contamination and its influence upon the bacteriological examination results. Samples were received in November 1912 from three separate springs in connection with a proposed new water supply. All three springs were from the same formation and indeed from the same hill. No. 2 was satisfactory while No. 1 and No. 3 showed evidence of contamination. A careful examination of the local conditions was recommended. At first it seemed difficult to account for any difference in quality since the three springs were obviously coming from the same strata and in each case were piped for about 100 yards from the springs, glazed open-jointed earthenware pipes being used. Further examination however disclosed, the fact that in springs 1 and 3 the pipes had been covered with a layer of bracken by the workmen employed