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29
SEWER MAINTENANCE. TREATMENT AGAINST RODENT
INFESTATION.
As part of the organised campaign throughout the country for the
eradication of rats in sewers, the whole of the sewerage system was prebaited
and poison baited twice during the year. I am indebted to the
Borough Engineer for the following information regarding this aspect of
rodent control.
The first of the treatment of sewers against rodent infestation for
1952 was commenced on the 7th January and completed on the 25th
January, the treatment having been carried out in conjunction with
other Authorities on the No. 4 Workable Area Committee. In spite of
difficulties in labour and transport, which prevented some of the No. 4
Area Authorities commencing treatment as arranged at the Committee
Meeting at St. Pancras Town Hall (26th September, 1951), a start was
made by the Sewers Department Staff on the pre-arranged date with the
assistance of three operatives from the Ministry of Agriculture, Infestation
Control Division. At the end of the first week the Ministry found
it necessary, due to absence of operatives on sickness leave, courses, etc.,
to withdraw the assistance of one of the operatives and the treatment was
continued with two operatives and their respective gangs until the 25th
January, when 739 manholes had been examined and 688 of these were
pre-baited. By cutting out the check visit after baiting with poison
bait, it was possible to complete the programme in the time normally
allocated to it. This check visit is not essential since the results and the
effectiveness of the treatment are determined from pre-bait " takes."
The same baiting procedure was adopted as on previous treatments.
Pre-bait was put down on the first and second days, followed by poisoned
bait on the third day, where a complete or partial take of pre-bait had
occurred. The pre-bait consisted of sausage rusk, and poisoned bait of
sausage rusk with 2½ per cent, zinc phosphide.
Table I below gives the results of this treatment tabulated for comparison
with those for the corresponding period in 1951: —

The comparative decrease in the proportion of complete takes to
number of manholes pre-baited is from 55·4 per cent. in 1951 to 43·6 per
cent. in 1952, while the increase of the proportion of partial takes to
pre-baits is from 24·4 per cent. to 24·8 per cent.—an increase of 0·4 per
cent.