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The staff carrying out this work during the period under review, comprised, in addition to the
Rodent Officer, 6 Assistant Rodent Officers, of whom one is foreman. Their main duty is operational.
In order to carry out this work in an area such as the City, the policy has been to seek the
co-operation of occupiers rather than the forceful method of issuing Statutory Notices under the
Act; these being used only in recalcitrant instances, and the response of occupiers generally has
justified this method.
Infestations fall under two headings: complaints, which are in effect requests for advice or
assistance, and those found as the result of surveys.
If not engaged on operational work, your Officers are employed on surveying defined areas for
the purpose of instituting Block Control.' A group of buildings surrounded on all sides by roads,
forms a convenient block. When the extent and number of infestations, if any, is determined, an
informal letter requesting the co-operation of the various occupiers is sent to each one. This letter
outlines the advantages to be gained by collective action and organised control measures carried
out by skilled operators simultaneously. It in no way minimizes any efforts taken by the occupier to
reduce the infestation in the past.
With regard to individual complaints, it is often the case that several requests for assistance
are received in a week, and these are usually situated in different parts of the City. These requests
cannot be neglected until such time as it is possible for your Officers to reach the site by the block
method, and accordingly a survey is made around the premises which are the subject of the compliant,
and a similar procedure as in the case of block survey adopted.
In every instance the occupier is advised of the two courses open to him to reduce the infestation
to a minimum. These are as follows:—
(1) Carrying out of specified control measures, the work to be supervised by the Rodent
Officer and effected by the occupier or his servant.
(2) Employment of a commercial undertaking to carry out the work.
If the occupier is unable or unwilling to adopt either of these methods, the Corporation may undertake
the work and recover the costs.
Until November 26th, 1944, this was at the rate of 2s. 6d. per hour for actual time on the premises,
plus the cost of materials used. Since the date mentioned, the hourly rate has been increased by
20 per cent, to 3s.
In every instance of infestation, advice on structural and incidental proofing is given, but the
difficulty of obtaining labour and materials renders much of this advice abortive.
The problem of conducting a survey of an area such as the City is full of complications, and the
time spent in one building interviewing occupiers, of which there may be several, can be considerable,
and, of course, is additional to the inspection. Also in trades such as catering establishments and
licensed premises, it is not convenient from the traders aspect, to make inspections and do operational
work during the peak hours.
For record purposes, the degree of infestation is classified in three categories: (a) Severe;
(6) Moderate ; and (c) Slight. Of the two latter headings, these can also be spasmodic or persistent,
according to their proximity to a severe infestation, food supplies available, and control measures taken
by the occupier.
From information recorded during the past year, the type of infestation is in the ratio 4 Black
(Ship) rat to 1 of Common rat.
Poisoning has been the principle means of extermination, and trapping a secondary measure.
The poisons used and advised by the Ministry of Food are Zinc Phosphide, Barium Carbonate,
Arsenious Oxide and Red Squill. Bait bases are Sausage Rusk, bread mash, soaked wheat, and
national flour, plus 10 per cent. Castor Sugar. Arsenious Oxide has only been used in non-food premises,
or in instances where prejudice to the other poisons is suspected. Wheat is used only where food
available renders other baits unattractive.
In almost every case of poison treatment, the pre-baiting technique has preceeded poisoning,
and this method has produced extremely satisfactory results. Premises known to be infested over a
number of years have been freed, or the infestation reduced to a minimum and maintained at that
level by periodical treatments.
The underlying principle of modern Rodent Control is to kill all rodents in an infestation as
quickly as possible, thus eliminating the natural increase in breeding. To do this, it is necessary
to ensure that the rats eat a lethal dose of poison before the warning symptoms appear. If a sublethal
dose is eaten, the animal is only ill and will recover, with the result that prejudice is obtained
and further attempts by using the same poison would be a waste of labour.
The pre-baiting method comprises setting unpoisoned bait for a period of four days at selected
sites. The number of baits depends on the extent of the premises and distribution of the rat population.
The baits are examined daily, and those taken or part taken are replaced. Any not taken after
two days are removed. On the fifth day, an increased quantity of bait evenly mixed with a selected
poison at a prescribed concentration is put down at all points where the unpoisoned bait was taken.
This is left down for two days and examined each day. After this period the residue of the poison bait
is picked up and destroyed.
The second phase, termed post-baiting, is to test the efficacy of the treatment, and therefore
unpoisoned bait, of a different nature from that first used, is placed at all points where poison bait
was taken. This in turn is left down for two days, and if not taken, the initial treatment can he
considered successful. Should, however, any of the post-bait be taken, a similar procedure as in the
first instance is followed and a different poison used. Again a post-bait is carried out, and if necessary
a third treatment. In most cases two treatments are sufficient to eliminate an infestation, and the
second and third treatments are always greatly reduced as regards numbers of baits used and the
time taken.
It will be seen that a campaign may comprise one or more treatments, but by this method the
infestation is cleared up quickly, and the risk of leaving a residual population to build up again in a
short time is eliminated.