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

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City of London 1931

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

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These Bye-laws are enforced by the officers of the Port of London Authority,
and the Sanitary Inspectors of the Port Sanitary Authority also call upon Masters
to put guards on their mooring ropes. But the well-known difficulties in regard to
the proper application and maintenance of position of rat-guards constantly occur,
and it cannot be said that the mooring ropes of the majority of ships in the Port of
London are at all times so guarded that a rat could not use them as a means of reaching
the shore. There is no doubt that rats very seldom voluntarily run along mooring
ropes, and the view is held that such rats as get ashore do so usually by some easier
means or accidentally in cargo.
(3) Methods of deratisation of :—
(a) Ships. The methods employed for the deratisation of ships are:—
(1) The burning of Sulphur at the rate of 3 lbs. per 1,000 cubic feet of
space, the period of exposure of vessels to the Sulphur Dioxide gas
thus generated being not less than six hours, and whenever time permits
twelve hours or even longer. Roll Sulphur, of good quality, is used,
and is burned in large shallow trays standing in larger trays containing
water. Owing to the large burning surface thus obtained, considerably
more Sulphur can be burned in one container within six hours than is
possible when buckets or pots are used.
Cylinders of liquid S02 (Sulphume) are employed in small
compartments and life-boats.
(2) The generation of Hydrocyanic Acid Gas by various methods. For
the destruction of rats a concentration of 0.2 per cent, of HON
is attempted, and the minimum period of exposure is two hours. If the
fumigation is for the destruction of insect life, bed-bugs and cockroaches,
two or three times this concentration is employed and the exposure is
twelve to twenty-four hours, according to the time available. The methods
of generating HCN employed are the spraying of liquid HCN, the
scattering of "Zyklon 'B'" or "Discoids" and the pouring of
liquid HCN into trays (Galardi process).
"Discoids" were introduced during the year. They are thin discs
of wood pulp saturated with liquid HCN. Each discoid holds half an ounce
of liquid HCN and they are packed in strong containers each holding
32 discs. They provide an easy and effective method of distributing HCN,
since they can be "sailed" into 'tween decks or wings of holds, and they
are also useful for the accurate dosage of small compartments. Moreover,
the spent discoids can easily be collected and removed after the
But in the hands of a competent Staff of fumigators all the methods
mentioned are effective, and can be applied to small cargo vessels or
large passenger liners without undue risk. Conversely, if the fumigators
are inexperienced or careless or there is imperfect organisation or lack
of discipline, any method of Cyanide fumigation may not only be
ineffective, but is very likely to result in fatal accidents.
In London ships are fumigated only when the holds are empty,
or very nearly so, except when there is definite evidence or strong
suspicion of the existence of rodent Plague on board. In the latter
event a preliminary fumigation with HCN would be undertaken
immediately, whether the holds were full or partly discharged, with the
object of destroying as many rats and fleas as possible and thus
diminishing the risk of the spread of the infection to the shore rats.
But, since complete deratisation of a loaded ship cannot be guaranteed,
the vessel would be again fumigated throughout when empty.
(3) Trapping. All vessels from Plague-infected ports are required to have
traps set on board, in order that specimens may, if possible, be obtained
for bacteriological examination. All other vessels, on which there is
evidence of rats, but not of such a number as to justify a demand for
fumigation, are required to have traps set in all spaces where signs of

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