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

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City of London 1957

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

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ted other mice and nothing but violence seemed to be effective. To open the containers and repack
was considered impracticable, hence the mice remained self-sufficiently housed and left
the containers at night only for exercise or spread to other attractive cargo.
In joint consultation with the P.L.A. it was decided that all the existing stocks of millet
sprays be assembled on two lighters and be treated with methyl bromide gas under the supervision
of the Port Health Authority, then to be taken to a mice-proof warehouse set aside specially for
this stowage. Ml future cargoes of this highly mice-attractive commodity will be examined by the
Port Health Authority before being admitted to the appointed warehouse.
Details of this operation were as follows:-
d.b. "BRISTOL" and d.b. "COLEHOUSE"
London Dock
2nd — 3rd December. 1957
Weight of Cargo Approximately 65 tons
Nature of containers Wooden cases, plywood drums, bags and baskets
Number of containers Approximately 1,200
Total capacity of holds 13,500 cu.ft.
Total capacity of cabins 1,500 cu.ft.
Total capacity fumigated 15,000 cu.ft.
Total weight of fumigant 23 lbs — (368 ozs.)
Concentration of fumigant 24.5 ozs per 1,000 cu. ft.
Exposure of fumigant 24 hours
The cargo was stacked in a reasonably compact bulk, allowing sufficient free space for gas
circulation, then covered with hatch boards and double tarpaulins.
The liquid methyl bromide was vaporised and expanded in a heated coil and entered the holds
under slight pressure to give it a velocity of 2 ft. per sec.
After 24 hours exposure, the spaces were tested for gas and declared 'gas free' before the
workmen discharged the cargo and transported it to No. 9 Warehouse. During the entire operation,
the Port Health representative was in attendance and NO LIVE RODENTS were seen after the

Some dead mice were seen in the cargo while in transit and it may well be that there were more, but their presence would not be a health hazard and it would be asking too much to have all the containers opened and re-packed only to recover the dead bodies.

Dead Rodents RecoveredLocationRatsMice
In transit-7
Killed by violence while loading3252
Total for operation44140
flats recovered were R. rattus and Mice of agricultural species.

All bodies were examined and found normally healthy.
So far as the number of bodies recovered and the absence of any live rodents is concerned, the
value of the operation is proved successful and there will be other dead bodies in the containers,
since it is to be expected that some would take refuge, in the compact millet sprays to escape the
chloropicrin lachrymator in the gas. Methyl bromide gas has a relative density of 4.5 and a high
power of penetration, so neither escaping rodents nor the nestlings could survive.
This method of treating a very difficult rodent problem which, hitherto has defied all known
practices may prove to be the best course of action and this principle of treating infested cargo
may be extended to similar operations under a gas-tight cover and in a suitable shed.
It is encouraging to report that the suppression of rats and mice aboard these thousands of
craft has been continued successfully for another year. There has been no faltering on the part of
the Rodent Inspector and no lack of collaboration from the Industry. Apparently the Industry
realises that the benefits that have accrued from ridding the lighters of rodents and has accepted
the policy of rat-proofing the craft within reasonable limits. The trend is that the Industry as a
whole has become quite rodent-conscious both afloat and at the repair yards.
In the repair yards, it often happens that where there are any indications of rodents present on
a lighter under repair, action is taken to destroy the rodents voluntarily in a manner approved by
the Authority and records kept of such operations for the information of the R odent Inspector.
Besides these voluntary operations others are carried out under the directions of the Authority
and supervised by the Inspector.