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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. But, 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 is undertaken immediately, whether the holds
are 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 is 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 rats are discovered.
The trapping may be carried out by professional rat-catchers or, in some
cases, by members of the crew, under the supervision of the officers of the
Port Health Authority.
(b) Premises in the vicinity of Docks and Quays. The Port of London Authority
constantly carry out methods of rat destruction ashore in the Port. Trapping is the
method principally employed, but the Authority are always ready to test any new
method of rat-destruction that is brought to their notice. The condition of all shore
premises is under the constant supervision of the Sanitary Inspectors and Assistant
Rat Officers of the Port Health Authority, who draw the attention of the officers
of the Port of London Authority to any signs of rat-infestation they may discover.
(4) Measures taken for the detection of rat prevalence in ships and on shore:—
Examination by Inspectors and Assistant Bat Officers, as already described.
(5) Ratproofing:—
Constant attention is devoted to ratproofing in ships and on shore premises.
The Port of London Authority fully appreciate that rat-proofing is the only rat
repressive measure of permanent value and in addition to issuing orders that all new
constructions on the docks shall be rat-proof, they have carried out all the recommendations
of the Port Health Authority in existing buildings.
In ships the appreciation of ratproofing is steadily spreading and Sanitary
Inspectors have been able to get much useful work done in ships, particularly in the
direction of opening up pipe casings and other structural harbourage.
Bats Destroyed during 1987.

See also Appendices XXIII. and XXIV.