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69
It is found from experience that the source of surface infestation
in domestic and other property is in the majority of cases traced
to defects in drainage systems and sewers. When such evidence
is found, appropriate action is taken by the Sanitary Inspectors
under the Public Health Act, 1936, to effect necessary repairs.
In this respect it is not always easy to discover faulty drains and
sewer connections, and this undoubtedly is the cause of many
long-standing infestations. By reason of its age much of the drainage
in Leyton does not conform to accepted standards of design and
construction. In those areas which contain groups of obsolescent
properties it is found that drainage defects are invariably due to
open clay joints or subsidence and failure of pipes owing to
inadequate concrete support. Added to this, bombed sites and
disused drains, perhaps imperfectly sealed from the sewer, provide
ideal harbourage and nesting places for rats. This must account for
many surface infestations.
Having regard to the foregoing, it will be appreciated that
the rat population on the surface bears some relationship to the rat
population below the ground—namely, in the sewers. Put simply,
if it were possible to confine rats to the sewers and drains—this
would mean, of course, that all sewers and drains in the Borough
would have to be in perfect order—the problem of surface infestation
would not be so acute. As it is, defective drains and sewers provide
a ready means of communication for rats migrating from the sewers
in search of nesting places and change of diet. Rats travel along
working sewers when scavenging for food, but they need dry
undisturbed places for nesting.
The only practicable method available to the local authority
for reducing the rat population in sewers is by poisoning. The
hazards of sewer baiting are well known; points at which poisoned
baits can be laid in the sewers are necessarily limited to the manholes,
and this, particularly where they are widely spaced, is one
of the causes preventing elimination of rats from the sewers. Further,
there is always the possibility of re-infestation from surface property
after treatment, and many of the baits may be washed away during
peak flow and flood periods. The probable state of the weather is
therefore an important factor when considering the time at which such
treatments are carried out. Because of these hazards some officers
are inclined to be a little sceptical as to whether results obtained
from sewer treatment justify the expenditure and labour involved.