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Sewer Maintenance
After considerable success in lessening the number of rats in sewers
which resulted from the use of new techniques and materials developed during
and after the war,the rat population appeared to have achieved a static level.
It was obvious that in order to bring about any further improvement new
materials or improved methods of treatment had to be sought.
Studies of the physiology of rats indicate that under optimum conditions
young rats reach maturity and ability to breed in a little over two months
after birth. This suggested that any new technique in order to be effective
must take this factor into consideration.
In May 1961 we began an experiment commencing with a complete pre-bait
of the entire sewage system with sausage rusk in order to provide some basis
for comparison in the future. This was followed by five poison treatments
at two monthly intervals, using sodium fluoracetamide added to the same bait.
A complete pre-bait was completed in May 1962. By comparison with the result
of the previous pre-bait it was possible to assess with a reasonable degree
of accuracy the effectiveness of the new methods. The results were very
encouraging. The percentage of all man-holes treated at which "complete
takes" (indicating the existence of heavy infestation) had been recorded,
fell from 7.4% to 2.5%, and it was further noted that some sections were now
completely free of rats, bait in good condition being untouched. The
experiment is being continued, and it is hoped that progressive reduction in
the rat population will be achieved with the gradual extension of the area of
rodent-free sections of the system.
Although it is early in the experiment, it is quite obvious that for it
to achieve the maximum success possible, it is essential owing to the interconnection
and complexity of the London sewerage systems that adjoining
Boroughs should carry out comparable treatments at the same time.
Business Premises
This scheme was introduced in 1943. Following inspection of commercial
premises and industrial sites, the Owners are encouraged to join the scheme.
The charge for the service is based on the extent of infestation, the number
of visits likely to be required, and the cost of labour and materials. In
an area with nearly nine miles of river frontage to the Thames and Lea this
enables the treatments to spread over a large number of premises and gives a
very satisfactory measure of control. It is appreciated by the Commercial
undertakers, and is a valuable part of rat repression work carried out in the
Borough. The income derived from this scheme amounted to £4,224,18,8 during
the year.
Dwelling Houses
319 complaints relating to dwelling houses received during the year.
No serious infestations were discovered, and practically all were traceable
to defects in the drainage system, or failure to seal off disused drains on
cleared sites.
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