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assistance. In nine instances complaints of very bad odours, suspected by the occupiers of
being due to decomposing rats under the floors were received. Investigation revealed no sign of
rat or mouse infestation, and in each case the cause of the odour which bore a very strong
resemblance to dead vermin, was traced to the overloaded electrical circuit, and consequent
heating of the P.V.C. cable in the plug box supplying current to electric fires. One occupier
had incurred costs of fifty pounds by his builder for the lifting of floor boards and stripping of
panelling in two offices.
The total of 520 infestations subject of treatment comprised 2 major and 66 minor infestations
of rats, and 33 major and 419 minor infestations of mice. Of the rat infestations, 2 major
and 41 minor were of common rat character, and the remaining 25 minor infestations came under
the Ship (Black) rat classification.
Treatment of these infestations entailed 5,022 visits for operational purposes and in the
process of control for rats 5,625 prebaits and 574 poisons baits were laid. This resulted in
a minimum estimated kill of 634 rats, and of this number, 284 bodies were removed from premises.
The use of Warfarin anti-coagulant rodenticides for the control of mice entailed the application of
10,220 initial baiting points and 986 bodies were recovered.
In 1945, the comparable figures were 399 rat infestations treated, 241 major (20 - 200 rats)
and 158 minor infestations, and control measures resulted in a minimum estimated kill of 10,038
rats of which 2,410 bodies were recovered.
In 28 instances structural ratproofing was carried out by owners or occupiers after the
application of control measures, and in 2 cases defective drainage resulting in Common rat
infestation was remedied. Incidental rat and mouse proofing in the nature of the removal of
harbourage provided by unnecessary and undisturbed accumulations has received detailed
attention, and the assistance given in this respect by the Director of Public Cleansing and
his Inspectors has been invaluable.
The low level of Ship (Black) rat infestation manifest in recent years has been maintained,
and the number of infestations of this nature (25), was for the second year exceeded by that of
Common Rat (43). In the year 1948, when 698 rat infestations were treated, 668 infestations
were Ship rat and 30 Common rat. Minor infestations of Ship rat have a high nuisance value and
often entail greater assiduity in respect of inspection and control measures than major infestations
distributed over a similar area. This is emphasized more especially where the odd rat or
two in search of food and water traverses the long tortuous ventilation ducts, lift shafts, and
service risers throughout buildings, leaving a trail of spasmodic evidence between roof and
basement, and it is only by a meticulous and methodical inspection that the evidence is found
and the best baiting sites selected. It is no trouble for this species of rat, with its climbing
abilities, to traverse long distances via ducts and up lift shafts, ropes and guides, as unrestrictive
movement is necessary for its well-being.
The Common rat infestations were, in the main, confined to building sites, which offer every
facility and are in every way conducive to infestation, but taking into consideration the vast
amount of re-development completed since 1950 and that in progress, rat infestation has not in
any way reached the degree viaualized and expected at the onset of reconstruction. The sites
were regularly inspected and the fullest co-operation has been received from the various
contractors.
In respect of the demolition of empty premises for re-development, it has been generally
accepted by occupiers of adjoining properties that they would, as the result, be subject to rat
infestation, but their fears have been unfounded, and no known infestations of Ship or Common
Rat have occurred from this source.
The low level of Common rat infestation in surface properties is in no small measure due to
the intensive and systematic periodical control measures applied in the City sewers.
It is the purpose of these control measures to check the build-up of the rat population in the
sewers, and thereby assist in preventing infestation of surface properties from this source via
defective drainage. Such measures also lessen the possibility of incidence of Leptospiral
jaundice or Weil's disease among the sewermen and others working daily in the sewers, since
this disease may be contracted by man when working or living in a rat infested environment.
Rats are the principal carriers of a spirochaete, Leptospira icterohaemorragiae which can be
carried in the kidneys of both Common and Ship rat. The disease can be caught by handling
Infected animals or coming into contact with bacterium in water or slime contaminated with
infected rat urine. Leptospiro can live for a considerable time outside the rat in damp conditions,
e.g. in the slime on the walls of sewers. Entry into the human body is usually by means
of scratches on the hands or through the mucous membranes.
The City sewer system comprises approximately 34 miles of traversable sewers, and about
5 miles of 9 inch pipe sewers, which cater for the courts and alleys. The accessible sewers
are, in the main, 3 to 4 feet in diameter, but certain sections are 11 and 17 feet. The daily flow
in the Greater London area is believed to be in the region of 400 million gallons. The entrances
providing access vary in depth from 10 to 35 feet.
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