London's Pulse: Medical Officer of Health reports 1848-1972

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City of London 1952

[Report of the Medical Officer of Health for Port of London]

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The bodies are placed in canvas bags which in turn are placed inside metal boxes, sealed and
labelled so that there is no risk of the escape of any rat fleas (luring their transit to the Laboratory.
The boxes are, of course, delivered by hand.
Examination of rats for evidence of plague being a public health measure, is now carried out at
the Government Laboratory at Colindale free of charge, representing a considerable saving in cost to
the Port Health Authority.
The routine Laboratory examination of rats found dead from an unknown cause has been a regular
practice in this Port for many years and it would appear to be a necessary and desirable precaution.
Even the practice of sending rats killed by trapping or poisoning or a proportion of the number so
killed would appear to be desirable.
Nevertheless the matter must be viewed objectively and in the light of a number of factors such
as the incidence of plague infected rats found in the Port over a number of years, the cost of the
service, the probability that the routine practice w ill have a bearing on the protection of the Port
against plague and finally in the event of a plague rat arriving in the Port the probability of the
transmission of the disease to the rat population in Port installations.
To take each of these features seriatim, a plague infected rat has not been discovered in this Port
since 1927, consequently the Laboratory examination of rats has been continued year after year for
some 25 years, without any positive result.
The incidence of rats in ships which increased considerably under war conditions has now returned
to a pre-war state and is indeed much less than the incidence in pre-war days. This is confirmed by the
diminishing number of rats destroyed in ships and the proportionately small number of deratting
certificates issued as compared to exemption from deratting.
The rat population in the Port is now so small and is under such strict control that it can be said
to be almost certain that the arrival of a plague infected rat would be highly unlikely to have any
serious significance. In other words, an epizootic could not be introduced into the Port for the simple
reason that there are insufficient rats to support an epizootic of this kind.
Consequently the routine examination of rats was abandoned early in the year and only rats
found dead in circumstances which might possibly indicate the presence of plague are being sent to
the Laboratory. No such circumstances have arisen during the year and consequently no rats were
sent to the Central Government Laboratory.
(3) Arrangements in the district for deratting ships, the methods used, and. if done by a commercial
contractor, the name of the contractor.
(a) The burning of sulphur at the rate of 3 lbs. per 1,000 cubic feet of space for a period of not
less than six hours.
The destruction of rats, whether it be by the open pot method or by sulphur gas is efficient and
the great advantage is that when applied in the holds of a ship the crew need not be put ashore.
Unfortunately a number of countries have, for some time past, refused to accept as valid, International
Certificates, where this method of rat destruction has been employed; consequently it has
fallen out of use.
(b) The generation of hydrocyanic acid gas by various methods. For the destruction of rats a
concentration of HCN at the rate of 2 ozs. per 1,000 cubic feet of space is required with a minimum of
two hours contact. If the fumigation is for the destruction of insect life, bed bugs, cockroaches, etc.,
two or three times the concentration is employed and the exposure increased up to twelve or even
twenty-four hours, according to the time available.
(c) "1080" and "Warfarin." The employment of the new rodenticides "1080" and "Warfarin"
are referred to elsewhere in this report.
The employment of "1080" has been used regularly throughout the docks with highly satisfactory
results. Its use in ships is still in the experimental stage but there is every indication that its
use in ships is equally satisfactory to its use ashore. A certain number of ships have been deratted by
this method in preference to the use of cyanide, resulting in a considerable saving in time and cost to
the shipowner.
Satisfactory results have been obtained from the use of "Warfarin" but a suitable bait, particularly
in granaries, with which to mix the poison which rats will take continuously in preference to the
grain or other form of cereal on which they are normally feeding, has yet to be found.
(d) Trapping. Trapping is seldom employed save for the destruction of isolated rats which have
not yet established themselves.
The following are the names of the firms approved for carrying out the deratting of ships:—
Messrs. Associated Fumigators, Ltd. Messrs. Fumigation Services, Ltd.
Messrs. London Fumigation Co., Ltd. Messrs. Ridpests, Ltd.
Messrs. Deodor-X Hygiene Services, Ltd. Messrs. Insecta Laboratories Ltd.


Rodents destroyed (bodies recovered) during the year in ships and in shore premises.

(1) On Vessels.

Number ofJan.Feb.Mar.AprilMayJuneJulyAug.Sept.Oct.Nov.Dec.Total
Black Rats169921371993442292391692002041051532.240
Brown Rats225-27
Species not recorded-
Rats examined
Rats infected with plague
(2) In Docks, Quays, Wharves and Warehouses.
Number ofJan.Feb.Mar.AprilMayJuneJulyAug.Sept.Oct.Nov.Dec.Total
Black Rats168172155168199136169907314493591,626
Brown Rats3051931994834402061833401714302192123,381
Species not recorded-
Rats examined-
Rats infected with plague------------