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In an area, such as the City, with approximately 1,000 catering establishments, plus innumerable
staff tea rooms, and three large markets, it is inevitable that a large quantity of food is
deposited daily into the sewers to provide subsistance for rats.
The increasing practice of the catering industry of installing waste food disposal units in
kitchens accentuates this problem, as the chewed-up waste after passing through the machine is
finally discharged into the sewers to be carried away in the flows.
This method of waste food disposal does, however, eliminate the use of swill bins, and the
storage thereof, which creates many difficulties. In many instances these bins have to remain
in the premises overnight, and inevitably constitute an attraction for rats, mice, flies, and other
insects. Where it is possible to put them out on the footway for collection next morning, they
still act as an attractant and in addition often create a nuisance to the public by offensive
odours, particularly in hot weather.
The importance of hygiene in relation to rodent control, embracing efficient waste disposal,
food storage, and elimination of incidental harbourage must be emphasized. This is essential to
the permanent control of commensal rats and mice, and control measures should be regarded as
supplementary to hygiene.
From the rodent control aspect the disadvantage created by the discharge of additional food
for rats into the sewers is far outweighed by the elimination of swill bins and their attendant
problems, and any improvement which can be introduced in the field of preventive control,
especially in catering premises, is to be commended.
In the phase of rodent control relative to sewers, innovations in the technique of applying
control measures and the use of new rodenticides have been introduced during the past ten
years. This applies principally to the "Direct" poison control method of application, and the
use of Monosodium Fluoroacetate and Fluoracetamide as the toxic agents.
Subsequent to the initial sewer treatment in December, 1943, it was the practice in accordance
with legislation, and in conjunction with the Metropolitan Boroughs contiguous to the City,
to carry out six-monthly controls. These measures comprised a two-day pre-bait, followed by
poison baiting in entrances where pre-bait was taken, and recording the result on the fourth day.
The poisons used were Zinc Phosphide, Arsenious Oxide and Alpha-Naphthyl-Thio-Urea.
The recorded result of the initial treatment was 355 pre-bait "takes" from 427 sewer
entrances baited, of which 185 were complete "takes", indicating the numerical density and
distribution of the rat population in the sewers at that time.
Continued six-monthly controls from January, 1943 resulted in a gradual reduction of the
pre-bait "takes", and the recording in the May, 1948 treatment was 118 "takes" of which 63
were complete. From then onwards an upward trend of pre-bait "takes" was experienced with a
proportional increase in complete "takes" until in December, 1950 the pre-bait "takes" were
225, of which 185 were complete, thus equalling the number obtained in the initial control in
December, 1943.
Little was known at that time of the movement of rats in sewers, but the position obtaining
at the time of the December, 1950 control appeared to indicate that the low basic level of the
residual rat population attained by the maintenance controls up to May, 1948 had not been maintained,
and that there was increased distribution, over a wider area plus the breeding increase
during the intervening period.
It was considered that in view of the time and effort expended on the maintenance controls,
drastic action was necessary to effect a further reduction of the residual rat population and to
this end discussions were held with the Scientific Officers of the Ministry of Agriculture,
Fisheries & Food, which resulted in their approval to the proposition that a series of "Direct"
poison controls with Sodium Fluoroacetate, technically known as "1080", should be applied at
quarterly intervals.
Thirteen controls of this nature were applied at quarterly intervals from May, 1951, and the
final control of the series was carried out in June, 1954. By applying the "Direct" poisoning
system the time expended previously was halved by reason of the elimination of the two days
required for pre-baiting, so that four treatments annually involved approximately the same number
of man hours as was needed for the six-monthly controls.
The first stage of the series comprised five treatments during the period May, 1951— May,
1952. In the initial control in May, 1951, 150 poison "takes" (three complete, 12 x ¾, 32 x ½
and 103 x ¼ or less) were recorded. In the second treatment in September, 1951 142 "takes"
(6 x ¾, 25 x ½ and 111 x ¼ or less) were recorded. The third treatment in December, 1951 produced
89 "takes" (one complete, 2 x ¾, 7 x ½ and 79 x ¼ or less). The fourth treatment in
March, 1952 showed a continued reduction in the poison acceptance, which was 53 "takes"
(one complete, 2 x ¾, 6 x ½ and 44 x ¼ or less). In the final treatment of the series in May,
1952, 424 sewer entrances were baited as against 306 entrances in the previous controls. The
inclusion of the 118 additional entrances would, it was believed, supply some information on the
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