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difficulty or not at all. The evidence obtained under this
section from drain air in the City of London is far more
convincing than that which I was able to obtain previously
from the sewer air of Hampstead.
(3) Lastly, it is shown that a test microbe, added in bulk to
the contents of the drains under suitable conditions of
splashing, can be recovered locally from the drain air
in great numbers, and can also be recovered from the air at
considerable distances (50 feet and 390 feet) from the point
at which it was added to the sewage.
From this evidence, no less than from that obtained by Major
Horrocks, it may be taken as conclusively proved that under certain
circumstances, at all events, sewage gives up its bacteria to sewer
and drain air. Such bacteria may form but a small proportion of
those present in sewer air: this is likely, for they would not
otherwise have escaped detection by previous observers. But it is
probable that the circumstances under which sewage gives up its
bacteria are common and ordinary circumstances in sewer and
drain construction, for the employment of selective culture media
has enabled me to discover them wherever so far looked for in the
air of drains and sewers.
The importance of the subject is plain, for though the
organisms which I have been able to detect in sewer air are not
in themselves known to be prejudicial to health, being for the most
part well-known saprophytes of the normal alimentary tract, yet
their value is evident as indices of the possible presence of more
harmful sewage-borne microbes.
Dr. Andrewes is now engaged on a further series of observations,
which, it is believed, will considerably strengthen the
evidence of the bacteriological impurity of sewer air. These observations
will shortly be published. It is interesting to note that
the latest results of scientific research justify the attitude of those
who have consistently held with the late Dr. Vivian Poore
that "there is more in stinks than we wot of," and who have refused
to allow the negative conclusions of an ill-developed
bacteriological technique to minimise the importance of emanations
of foul-smelling sewer gas. In view of the knowledge that
has now been acquired it is eminently desirable that the whole
question of sewer ventilation should be thoroughly reconsidered.