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RODENTS.
The Rodent Control Scheme which has now been in force in the dock
groups since 1941 continues to work satisfactorily and it is believed that
the Port of London Authority, their Tenants and the various shipping
companies are satisfied with the results.
Nevertheless your Medical Officer is not himself satisfied that even
better results could be achieved by the use of methods of rodent destruction
which have recently been discovered and are in extensive use in the
United States of America.
Present methods are based on prolonged and carefully controlled
scientific experimental work carried out at the Bureau of Animal
Population, Oxford and by members of the staff of the Bureau working in the
London Docks in collaboration with your Medical Officers and his staff.
Very briefly the principle consists of pre-baiting with a known rat
attractive bait such as sausage rusk or flour and sugar or moist wheat
and, after good takes are registered, introducing a poison such as zinc
phosphide or arsenic or red squill.
A count is made of the amount of pre-bait taken and then of the amount
of poisoned bait taken and from this the number of rats destroyed is
deduced. Post-baiting with a different bait than that first employed is
carried out after an interval of one or two weeks to ascertain if there is
any residual rat population and if necessary a different poison is laid to
destroy this residue.
In addition to poisoning, trapping is occasionally resorted to though
it is a less satisfactory method than poisoning but is more applicable to
small rat populations in ships and may occasionally be quite successful
in destroying a mouse population. The disadvantage of trapping lies in
the fact that it is seldom that the whole colony can be thus eliminated
while the residue becomes trap shy and indeed shy of any method of destruction.
In recent years a number of "super poisons" have been elaborated in
the United States and one of them "1080" (sodium fluoro-acetate) is now
extensively used in the Western Hemisphere not only for the destruction of
rats on shore but also in ships. It will readily be appreciated that any
method which eliminates the costly process of using poisonous gases, such
as hydrogen cyanide, so long as it is equally efficient, would be welcomed
not only by Port Health Authorities but also by shipping companies.
Unfortunately "1080" cannot yet be obtained in this country but the
small quantity that has been made available in the port has sufficed to
reveal its remarkable properties. "1080" is intensely poisonous not only
to rodents but to all animals including human beings and must, therefore,
be used with great care to avoid any risk to human and to animal life
other than the rodents that it is intended to destroy. Such precautions
are fortunately quite simple and if carefully folio-wed render the operator
free from risk.
It is very attractive to rats and mice and can be used without any
pre-baiting in the form of a solution of 0.25% in plain water. Rats
however shy of other methods for their destruction take the liquid freely
and many of them can be found dead within a few feet of the container.
It is to be hoped that "1080" will be manufactured in this country in
the near future thus overcoming the difficulty of finding dollars for its
purchase in the United States of America and your Medical Officer is
confident that remarkable results would emerge from its use in the Port.
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