AIR 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. 



Delepine 1 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. 



Horrocks 2 , 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. 



Andrewes 3 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. 



8 Local Government Board Medical Officers Report ', 1906-7, p. 183; 1907-8, 

 p. 266; 1910-11, p. 387. 



