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proportion of 95 per cent, sausage rusk and 5 per cent. Zinc
Phosphide.
Treatment of the first areas commenced on December 6th,
1943, and continued during the subsequent weeks until the
whole Borough was completed on January 16th, 1944. Each
area was begun on a Monday, and on that and the three following
days unpoisoned bait was laid. Poison bait was laid on Friday,
and the results checked on Saturday; thus the complete treatment
of any area took one week. The amount of bait eaten
is divided into four categories; viz.:—(1) No take, (2) small
take, (3) good take, (4) complete take, and the estimate is
based on the amount remaining. These takes are recorded for
the previous day, i.e., Monday's take is recorded on Tuesday,
before placing Tuesday's bait, and so on. The weight of bait
placed in each manhole was 6 ozs. of unpoisoned pre-bait, and
12 ozs. of poisoned bait.
RESULTS AND CONCLUSIONS.
Before setting out the results of the campaign, it is advisable
to indicate how the estimated number of rats killed is obtained.
From experiments carried out by the Ministry of Food, it
is calculated that two-fifths of an ounce of the poison bait is
a lethal dose. This is a conservative estimate and has been
determined by weighing the contents of the stomachs of dead
rats. Thus, if the total weight of poisoned bait taken is
known, it is possible to estimate the number of rats killed.
Appended below is a summary of the results, from which
it will be seen that the number of manholes baited was 1,109,
and the estimated number of rats killed 10,898.
One can only conclude from these results that the careful
and thorough preparation was worth while. It is not, however,
anticipated that any sudden falling off in the complaints of
rats will be felt; rather will this be a gradual process. The
second treatment was commenced on the 17th January, 1944,
and the results of this treatment show that there is a substantial
reduction in the rat population in the sewers, bearing testimony
to the efficacy of the methods used.