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As in the past, the low level of Common rat infestation is no doubt due to the systematic
control measures applied in the City sewers at quarterly intervals. It is the purpose of these
treatments to check the buildup of the rat infestation in the sewers, thus preventing infestation
of surface premises from this source via defective drainage.
In this respect, four "direct" poison controls with Fluoracetamide "1081" and an overall
test baiting were applied. These controls comprised the second phase of a series of controls
with "1081" which are designed for completion in 1960 and which it is hoped will provide comparable
information to that obtained as the result of the Mono Sodium Fluoroacetate "1080"
controls completed in 1956.
On completion of the first series of four "direct" "1081" poison controls, September, 1957,
it was decided, as the result of discussions held with the Technical Officers, London Division,
Ministry of Agriculture, Fisheries and Food, to carry out three overall test baitings with the
object of obtaining similar information to that supplied by the tests conducted on completion of
the "1080" series of "direct" poison controls, June, 1956, and preceding the institution of the
first "1081" series.
Three such tests were applied, starting on the 10th October, 1957 , 5th December, 1957,
and 6th March, 1958, respectively.
For the purpose of the first test, three weeks after completion of the first series of poison
controls, 400 sewer entrances were each baited with 4ozs. baits of soaked wheat, and the baits
were left down 5 days. On examination 27 "takes" (15 complete, 9 x ¾, 1 x ½, and 2 x ¼) were
recorded.
In the second test 8 weeks later, 406 sewer entrances were baited, each bait being 4 ozs.
damp sausage rusk, and these were left down 5 days. The recorded result in this instance was
69 "takes" (58 complete, 3 x and 8 x ½). The weather conditions during both these tests
were fairly good, and although some rain was experienced it did not have an adverse effect on
the recordings.
For the final test, 13 weeks later, and 6 months after completion of the first series of
poison controls, 394 entrances were baited, and the baits, each 4ozs. of soaked wheat were
left down 7 days. The recorded result was 194 complete "takes".
In this instance, bad weather was experienced. There was heavy rain on the second day
when baiting was completed, this being followed by a heavy snowfall on the third day. It was
impossible under the circumstances to record how many of the "takes", observed as such, were
possibly washed away.
Accepting the recorded "takes" of the final test as all "taken" and not washed away, the
progressive rate of the complete "takes" in the three tests is 15, 58 and 194 respectively.
The comparable results of the tests conducted after the "1080" series, and prior to the
institution of the first series of "1081" controls was 36, 84 and 165 complete "takes"
respectively.
It is reasonable to assume, from wide experience of sewer control under all weather conditions
that approximately 15% of the 194 complete "takes" recorded in the final test were
washed away. This is, in some measure substantiated by the similarity of the poison "takes"
in the first control of the second series, and that of the initial control of the first series,
December, 1956.
On this basis, the pattern of the test results after "1081" controls is similar to that of the
test results following the "1080" direct controls.
The first poison control of the second "1081" series was applied immediately on completion
of the final test. A total of 394 sewer entrances were treated each bait being 4ozs., comprising
sausage rusk and water solution of "1081" at a concentration of 1% by weight. The baits were
left down 4 — 6 days before clearance and on examination 91 "takes" (14 complete, 17 x ¾
26 x ½ and 34 x ¼) were recorded. A total of 28 bodies were found and these were in the flows,
in several instances a considerable distance from the sites of the baits. The weather in this
instance was ideal and the majority of the bait residue was in good condition when cleared.
The comparable result of the initial "1081" control 1956, was 87 "takes" (8 complete,
7 x 39 x ½ and 33 x ¼) ex 394 entrances baited, and 52 bodies were recovered. The estimated
amount of poison bait accepted in the first instance above is 193 ozs. and in the latter 164 ozs.
The second control of the series was applied on the 5th June, when 401 entrances were
baited. The baits after being down 4 — 5 days were examined and the recorded result was 45
"takes" (25 complete, 8 x ¾ 11 x ½ and 1 x ¼) 14 bodies being found. In the latter part of this
control continuous heavy rain was experienced, and 27 baits were recorded as washed away.
This could possibly apply in some instances of the 25 "takes" recorded as complete.
In the comparable control of the first series, the result was 60 "takes" (11 complete,
7 x ¾ 18 x ½ and 24 x ¼) ex 401 entrances baited, and 34 bodies were found. In this instance
the weather was fine.
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