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24
an unnecessary waste of food. Research work, however,
proves that rats take some time to travel, and therefore ample
time must be given to ensure that all the baited points are
visited. Again, in dealing with a surface infestation it is
possible to lay the bait between the point where the rats emerge
and the point where they feed. This is not the case in the
sewers, as food may be found at any point before the bait is
reached.
The food, mixed or treated with poison, is laid on the
fifth day.
A preliminary survey of all soil manholes in the Borough
was made and details regarding position, depth and suitability
for baiting, were recorded on survey sheets, regard being paid
to the possibility of flooding. The Borough was then divided
into a number of workable areas, each containing approximately
70 to 80 manholes. From the survey sheets, lists were prepared
of manholes where direct baiting could not be carried out, and
those manholes, where possible, were fitted with iron traps
to which were attached a piece of stout rope.
The positions of the manholes were next plotted on a large
scale map, and a route worked out which permitted of each
area being baited in one day, i.e., every manhole in the area
was baited on the same day.
Bait is placed in position by a special "bait depositer"
devised and supplied by the Ministry of Food.
During the preliminary survey all manholes which it was
intended to bait, were identified, covers loosened, and greased
where necessary, and any accumulation of sludge or deposit
swept off the benching.
APPLICATION AND TREATMENT.
The treatment was carried out by gangs of men, each gang
consisting of two men from the Borough Engineer's Department,
and one volunteer from the Civil Defence Services. The latter
were trained by the staff to act as baiters and recorders.
The bait base used was damp sausage rusk, the poison
used on the final day being Zinc Phosphide mixed in the