The experimental bacterial treatment of London sewage : being an account of the experiments carried out by the London County Council between the years 1892 and 1903 / by Frank Clowes and A.C. Houston.

  • London County Council
Date:
1904]
Catalogue details

Licence: In copyright

Credit: The experimental bacterial treatment of London sewage : being an account of the experiments carried out by the London County Council between the years 1892 and 1903 / by Frank Clowes and A.C. Houston. Source: Wellcome Collection.

    143/356 (page 93)
    93 It is evident from these results that the bacterial treatment of the sewage in the coke-beds did not effect any marked reduction in the number of organisms growing at blood-heat; indeed, the reduction was less as regard^ these germs than as regards the bacteria growing in gelatine at 20° C. . Although gelatine is doubtless a more favourable medium than a.gar for the growth of bacteria of all sorts, it is not the difference of nutrient medium, but of temperature which chiefly accounts for the difference in the numbers under the two sets of conditions. As a matter of fact, the number of bacteria in sewage capable of growing at 37° C. is both actually very great and is very great also in relation to the total number of microbes growing at the ordinary temperature, the reason apparently being that so many of the micro-organisms found in sewage are derived from the intestinal discharges of animals, e.g., B.coli, which microbe has been shown to be present in numbers usually exceeding 100,000 per cc. In pure waters, the number of “ blood-heat ” bacteria is usually small, and the ratio of these bacteria to the number of germs growing at the ordinary temperature is likewise small. Although a large number of “ blood-heat ” bacteria is considered an unfavourable characteristic in an effluent, it must not be supposed that all the different species of microbes capable of growing at 37° C. are harmful. Many found in sewage and elsewhere in nature are, so far as we know, quite unobjectionable, e.g., B. subtilis, B. mesentericus, B. mycoides, etc. On the other hand, others are decidedly objectionable and may be pathogenic under certain conditions, e.g., B. coli and B. jproteus (certain forms), and some are definitely pathogenic, e.g., B. pyocyaneus. On one occasion B. pyocyaneus was isolated from a sample of Crossness crude sewage. 1 c.c. of a 24 hours’ broth cultui'e (at 37° C.) of this microbe injected subcutaneously into a guinea-pig killed the animal in less than 24 hours, and the organism was recovered in pure culture from the heart’s blood, spleen, etc. On November 1, 1899, B. pyocyaneus* was isolated from tooo c.c. of the effluent from the secondary coarse bed (series A) at Barking, t A guinea-pig injected subcutaneously with 1 c.c. of a twenty-four hours’ broth culture (at 37° C.) died in less than 24 hours, and the same micro-organism was isolated in pure culture from the heart’s blood of the guinea-pig. So far as may be judged by a rise or fall above or below the mean, the figures show’ that, both as regards the crude sewage and the effluents, there was a decided parallelism between the number of bacteria growing in agar at 37° C. and the number growing in gelatine at 20° C. Similarly, a rise or fall above or below the mean in the number of bacteria capable of growing in agar at 37° C. in the crude sewage wTas nearly always coincident with a rise or fall in the number of microbes in the corresponding effluents from the 13-foot coke-bed. In conclusion, and by way of addition to the chief results which wTere obtained during the progress of the enquiry, it is to be noted that the number of bacteria capable of growing in agar at blood-heat in Cross- ness crude sew’age is usually over three millions per c.c., and more than * See Fig. 12. t In certain epidemics of diarrhoea occurring in human beings, B. pyocyaneus has been isolated from the stools of the patients and has been regarded in these eases as the causal agent.