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Mr. Carter reports as follows:—
"Organisation and procedure during the year was similar to that of previous years, and in
compliance with the provisions of the Prevention of Damage by Pests Act, 1949, comprised
inspections of properties to ascertain the presence of rats and mice, treatment of any properties
found to be infested, and periodical maintenance controls for the destruction of rats in the City
sewers.
The co-operation of occupiers and owners of properties has been satisfactory, and no difficulty
has arisen which necessitated statutory action to resolve the problem.
During the period under review 3,793 occupancies and properties were inspected, the varying
types of properties ranging from large blocks of offices, riverside food warehouses, catering
establishments, factories and shops, to domestic dwellings.
A total of 675 infestations of rats and mice were treated, and of this number 310 infestations
were notified, and 365 were found as the result of inspections. The total comprised 20 major and
219 minor infestations of rats, and 116 major and 320 minor infestations of mice.
The rat infestations were mainly of Ship rat (Black) nature. Applied control measures
entailed 6,013 visits for operational purposes, and during the course of the treatments 16,508
initial baiting points were selected, 25,339 pre-baits were put down, and 2,124 poison baits
were laid. These measures resulted in a minimum estimated kill of 1,630 rats, and 955 bodies
were recovered. In addition, 91 rats were destroyed by means of traps. The use of anti-coagulant
rodenticides for the control of mice resulted in 1,181 dead mice found.
In 36 instances structural rat-proofing was carried out by occupiers, and in ten instances
incidental rat-proofing was effected by means of removal of rubbish and other accumulations
providing harbourage.
The downward trend of rat infestation has continued, and a further decline in the number
of infestations and numerical density has been experienced. There has, however, been an
increase in mice infestation, and this is due in the main to the careless or thoughtless disposal
of waste scraps of food, food wrappers, etc. by the daytime population of premises.
Infestation of common rat character in surface properties was again extremely low, and
only two such infestations were found and treated. This is possibly due in no small measure to
the systematic periodical maintenance treatments carried out for the control of common rats in
the City sewers. It is the purpose of these treatments to check the build-up of the common rat
population in the sewers, and thereby assist in preventing infestation of surface properties from
this source via defective drainage.
Subsequent to the initial sewer treatment in December, 1943, it was the practice in
accordance with legislation and in conjunction with Metropolitan Boroughs contiguous to the
City, to carry out six-monthly controls. These control 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-NaphthyThio-Urea.
The recorded result of the initial treatment was 355 pre-bait "takes" of which 185 were
complete "takes", this indicating the numerical density and distribution of the rat population
of the sewers at that time.
Continued six-monthly maintenance controls from January, 1945, 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 the pre-bait "takes" was
experienced, with a proportional increase in complete "takes", until in December 1950, the prebait
"takes" were 225, of which 185 were complete, thus equalling the number of complete
"takes" obtained in the initial control in December, 1943.
Little is known scientifically of the movement of rats in sewers, but the position obtaining
at the time of the December, 1950 control appeared to indicate that there was a distribution
over a wider area, plus the breeding increase during the intervening period of six months between
controls.
It was considered that in view of the time and effort expended on the maintenance controls,
drastic action was necessary to effect a reduction of the residual rat population, and to this end
discussions were held with the Technical Officers, Infestation Division, Ministry of Agriculture
and Fisheries. As a result, it was agreed that as from May, 1951 a series of treatments,
comprising direct poisoning with Sodium Fluoroacetate, technically known as "1080", be
carried out at quarterly intervals. This poison is in powder form, and as a precautionary measure
is tinted blue with nigrosene dye. It is extremely lethal to man and animals, there being no
known antidote. It should never be handled without rubber gloves being worn, and its use
should be controlled by a responsible person, both in its dispensing and distribution.
A total of 13 treatments at quarterly intervals, in three stages, have been applied since
May, 1951, the final control of the series being carried out in June, 1954.
As in the previous controls, the sewer area was divided into seven sections, each having
approximately 63 sewer entrances. It was decided not to bait every entrance in each sector,
and 306 of a total of 427 entrances usually pre-baited were selected. This number comprised 225
entrances where pre-bait "takes" were recorded during the December, 1950 treatment, plus 81
entrances which showed a negative result during that control, but where "takes" were recorded
during either of the two previous treatments.
By applying the direct poisoning system the time 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 by the six-monthly treatments.
The labour used to work a sector, comprised a sewerman to raise the entrance covers, and
two operators. One operator deposited and picked up the baits, and the other recorded, lowered
and raised the container when the poison was cleared up.