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The bait was carried in large tins with lids, and the operator depositing the bait wore rubber
gloves which he put on before leaving the depot. Each bait was 4 ozs., this amount being
measured by means of a metal mug holding that amount.
As each sector took approximately five and one-half hours, a break was necessary, and each
term adjourned to a public convenience, where the recording operator who had not touched the
poison bait turned on the wash basin tap to enable the depositing operator to wash his gloves
before removal.
Every precaution was taken during the mixing of the poison bait and rubber gloves were
worn. The baits comprised sausage rusk and water in equal parts by weight, evenly mixed at
a concentration of 1% by weight. The bait was mixed in batches of 100 ozs., the required
amount of rusk being added to the solution and well stirred. After use every utensil was
thoroughly washed under a running tap.
In the treatments prior to this series it was the practice to take the poison bait recording
from the top of the entrance and leave the bait to decompose, but in the instance of these treatments
it was imperative that poison bait not taken be cleared up. While this entailed descent
of the sewer shafts, it also enabled a reasonably correct recording to be made.
The procedure of application was to bait three sectors on Monday, examine and pick up the
poison on Thursday; three sectors on Tuesdays, examine and pick up on Friday; and one sector
on Wednesday, examine and pick up on Saturday, thus completing the whole area in one week.
The first stage of the series comprised five treatments during the period May, 1951—May,
1952. In the initial control in May, 1951, 150 "takes" (three complete, 12×¾, 32×½ nd
103×¼ or less) were recorded. In the second treatment in September, 1951, 142 "takes"
(6×¾ 25×½ and lll×¼ or less) were recorded. The third treatment in December, 1951,
produced 89 "takes" (one complete, 2×¾, 7×½ and 79×¼ or less). The fourth treatment in
March, 1952, showed a continued reduction in the poison "takes", which were (one complete,
2×¾ 6×½ and 44×¼ or less), a total of 53. In the fifth treatment in May, 1952 424 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 movement and
build-up of rats in lengths of sewers not treated for 18 months. The result of this treatment
was 20 "takes" only (3×½ and 17×¼ or less), the lowest yet recorded. A feature of this
treatment was that only three "takes" were obtained from the 118 additional entrances baited.
The fall in the number of poison "takes" was extremely satisfactory, but the possibility of
some poison prejudice having developed was visualized, and in order to be reasonably satisfied
on this point, and at the same time test the efficacy of the measures applied, a test baiting of all
available sewer entrances was applied after a lapse of three weeks. To overcome any possible
biat prejudice also, bread rusk moistened with water in equal parts by weight was used, each test
bait being 4 ozs. A total of 417 sewer entrances were test baited and the bait left down for two
days, when examination showed 35 "takes" (seven complete, 3×¾ 10×½ and 15×¼ or less).
Altogether 104 lbs. of test bait was put down, and the estimated amount taken was 72 ozs. only.
This is a very satisfactory reduction on the pre-bait recording of December, 1950, when 225
"takes" (185 complete, 29×½ and 11×¼) were obtained and the estimated amount taken was
67 lbs.
The intermediate stage of the series comprised four treatments during the period September,
1952 and June, 1953. The number of entrances baited was approximately 315 in each instance
and the "takes" were consistently low. They were 13, 14, 16 and 11 respectively, and with one
exception were in the ½ and ¼ or less category.
Subsequent to the fourth poison control and after a lapse of three weeks, 413 sewer
entrances were test baited and a total of 105 lbs. was put down and left for two days. Examination
showed 23 "takes" (14 complete, 6×½ and 3×¼), and the estimated weight was 71 ozs.
This test result shows little change to the test of the previous year and the increase in the
complete "takes" is in no way significant.
The third and final stage comprised four treatments during the period September, 1953 to
June, 1954, and as in the second stage the poison "takes" were consistently low, the recordings
being 21, four, five and four respectively. The annual test baiting of all available entrances
was applied three weeks after the final poison control, and the recorded result was 26 "takes"
(15 complete, 5×¾, 3×½ and 3×¼ or less) out of 405 entrances baited. In this instance 101 lbs.
of test bait was put down and approximately 82 ozs. taken.
During the course of this series of treatments, 262 bodies were found at the base of the
sewer shafts or in shallow flows close to the base. This number does not include those found
subsequently by the sewermen during their routine work, along the lengths of sewers and in dead
ends. In one instance 15 bodies were found in a group near to an entrance where a complete
"take" was recorded, and no doubt many bodies were washed away in rapid flows.
The weather conditions during these treatments can have an important effect on the results.
If there is an appreciable amount of rain prior to, and during a treatment, this has the effect of
making the entrances very wet and sludgy, resulting in the baits becoming sodden, and in the
event of heavy rains the baits can be washed away by the charged up flows. Fortunately the
periods selected for these direct poison controls was, in the main, fine, and of the 90 days which
the treatments occupied, only four were sufficiently wet to have an adverse effect.
From an analysis of the detailed records collated it does appear that the combination of
quarterly treatments and the use of Sodium Fluoroacetate has produced the results it was
considered could be obtained, and that an irreduceable minimum of the rat population in the
sewers had been achieved, thereby justifying the use of such highly toxic poison, and the labour,
care and thought taken in the dispensing and application.
Subsequent to the completion of the series, discussions were again held with the Technical
Officers, Infestation Division, Ministry of Agriculture & Fisheries, to decide (a) continuance with
Sodium Fluoroacetate, (b) alternative control measures. The question of returning to six
monthly periods as prior to May, 1951 did not arise, as it was previously agreed that the
quarterly controls were preferable.