The prevalent fear of the deleterious effect of escaping sewer gas is one that has been magnified to an unwarrantable degree. Among bacteriologists it is very generally recognized that none of the dreaded diseases to which the human kind is susceptible are transmitted by gases. The one possible harmful effect recognized in sewer gas by scientists is that produced by carbon monoxide. Sewer gas often contains, from escaping illuminating gas, sufficient carbon monoxide to produce the poisoning effect characteristic of that gas but the possibility of danger is quite remote. The leakage of sewer gas is detected by the sense of smell sooner than in almost any other way. While leaks in sewer pipes are unhygienic in that they are conducive to undesirable atmospheric conditions, they should not be looked upon as the agents through which transmissible diseases are carried.

Fig. 112. - Method of removing obstructions from a stopped drain-pipe.

To the average person the term sewer gas conveys the impression of a particularly loathsome form of vaporous contagion, capable of distributing every form of communicable disease. To the scientific mind it means no more than a bad odor. Sewer gas is really nothing but ill-smelling air.