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63
Baiting of Sewers.— The Borough Engineer has kindly supplied
me with the undermentioned information of the treatments carried
out in the Council's sewers in connection with the scheme:—
"In collaboration and at the suggestion of officials of the
Ministry of Agriculture, Fisheries and Food, an experiment was
conducted over the whole Borough using 12 oz. bait blocks (com
prising pinhead oatmeal, sugar, technical white oil and Warfarin
No. 5) suspended in each manhole just over the benchings.
Approximately 1,160 manholes were each treated with one block at
intervals of three months. The efficiency of the blocks will be
gauged from a pre-experiment census taken in October, 1958, and
a further census to be undertaken in January, 1960.
Inspection of the blocks during the year's treatment has shown
them to be susceptible to mould growth in the humid atmosphere
usually found in sewer manholes and it is considered that this will
reduce palatableness. There was evidence that many blocks were
partly consumed and in a small number of cases whole blocks were
missing which could, of course, be accounted for by sewer surcharge.
No indication of the Warfarin block treatment's efficiency will
be known until the proposed census to be undertaken by Ministry
officials next year, but it is clear that a block treatment is simple
and safe to operate and has much to commend it, particularly
economy of labour."