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.

    155/196 (page 139)
    Sewer and drain air. The bacteriology of sewer and drain air is of considerable interest and importance. The earlier investigators, Haldane and Carnelley, Laws, Andrewes and Laws, all found that the air of sewers contained but few bacteria, and those found appeared to be of the same nature as those in the outside air and to be so derived, and not from the sewage. In both, for example, a large proportion consisted of moulds while the numbers present increased or decreased with the degree of ventilation of the sewers. Delepine1 found that the average number of microbes in the air of the Manchester sewers examined during the months of May, June and July (mean of 33 observations) was about 855 per 1000 litres. Of these 552 were bacteria and 303 moulds. More recent work has not invalidated the general truth of these findings although it has demonstrated that under ex- ceptional circumstances sewage bacteria may be present in sewer air and, much more frequently, in drain air. Horrocks2, in 1897, showed that specific bacteria present in sewage may be ejected into the air under certain conditions, such as the bursting of bubbles at the surface of the sewage, or the separation of dried particles from the walls. The alternate moistening and drying of the walls when the flow of sewage is intermittent, in his opinion, would favour such detachment. Andrewes3 has recently carried out three important series of investigations. He showed that under certain circumstances characteristic sewage bacteria are to be found in the air of drains and sewers. The evidence for this is based upon a careful study of the characters of the bacilli found in sewer air, using newer and better methods than hitherto employed. For example, the streptococci of drain air, when tested as to their biological characters, were found to correspond with those of sewage, and only to a slight extent with those which chiefly 1 Special Report to Manchester Committee, 1909. 2 Proceedings of Royal Society, February 7, 1907. » Local Government Board Medical Officers Report, 1906-7, p. 183; 1907-8, p. 266; r9io-n, p. 387-