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On the survey side of the work, 2,636 properties were surveyed. This embraced all types of
property, ranging from large blocks of offices, riverside food warehouses, factories, kitchens and
workshops to domestic dwellings. The time spent on inspection of large blocks is very considerable,
and although often with negative results, it is necessary for the success of collective action.
Indirect poisoning has again been the principle means of extermination and in every instance
pre-baiting has preceeded poisoning. While it may appear to be a long and tedious procedure to
pre-bait for four to five days before poisoning, the results obtained have fully justified the time so
spent. This applies to minor as well as heavy infestations. While it is not claimed that complete
clearance is obtained in all cases, it can be said that a high proportion of a rat population is destroyed
in one blow.
Much of our work has been in dealing with infestations which in the past have been the subject
of unorganised and haphazard control measures. Often the occupier has used several proprietary
poisons and expended much labour before seeking advice, and although a few immature rats may
have been destroyed, the mature and productive adults often remain and the net result is a poison
prejudiced population.
Of the number of premises inspected, 412 were found to be infested in varying degrees and in
each instance control measures were applied. In 315 properties one course of treatment was sufficient
to abate the nuisance, and of the remainder, 63 received two periodical treatments, and 34 needed
three or more during the year, making a total of 512 operations completed.
This entailed 6,543 re-visits for operational purposes, and to provide some indication of the
amount of work this involved, 14,991 initial baiting points were selected. A total of 63,224 pre-baits
were put down, and 8,672 poison baits were laid.
These measures resulted in an estimated kill of 8,658 rats and of this number, 25 per cent, or
2,087 bodies were recovered on completion of the work. This figure does not include dead rats found
subsequently by occupiers when harbourage was removed, unless they were actually seen by an
operator. Trapping, as a secondary control measure was the means of destroying 480 rats, and added
to those found after poisoning, a total of 2,560 bodies were taken from premises by this department.
The number of bodies recovered in relation to the estimated kill appears to be high, but the
estimate is very conservative, and could reasonably be increased by at least 25 per cent. The
calculation is based on common rat extermination and 80 per cent. of infestations were of
Ship (Black) rat character. The latter animal being much smaller than the common rat, naturally
consumes less food and consequently a smaller quantity of poison-bait constitutes a lethal dose. For
example, in one property subject of Ship (Black) rat infestation, 42 bodies were recovered, and
10 ozs. of poison bait had been consumed. On the common rat basis of calculation this amount of
poison taken would give an estimated kill of 25 rats, and it is this figure which is recorded. While
these figures are a source of satisfaction to the operators and provide some evidence of the results of
their work, the real test of the efficacy of the treatment is the absence of live rats in premises.
Taking into consideration the nature of the property in the City and the character of the rat
infestations treated, very few complaints of corpse smell have been received. In instances where this
nuisance has resulted, assistance has been given in the appropriate action to clear it as quickly as
possible.
A considerable number of mice infestations have been treated with satisfactory results in all
types of property. It is not possible to give an estimated kill, as the amount of poison bait consumed
is so very small. Altogether 207 bodies were recovered after various treatments and as in the case
of rats, their absence, at least for a reasonable period is the main object.
An important part of rat repression is the periodical Sewer Maintenance Treatment against
common rat, and during the year three treatments were carried out. These took place in January,
May and December. This work resulted in an estimated kill of 2,910 rats of which 105 bodies were
found at the base of entrances. The effect of these treatments must be considered in relation to surface
infestations of common rat as there is always a possibility of a connection between the two. Figures
as accurate as it is possible to obtain are kept of these treatments, and by analysis of sector recordings
it is possible to define the centres of residual populations where conditions are most favourable
for infestation and from which the population, if allowed to build up is distributed over sections
found to be free as the result of the last treatment. It is the purpose of these maintenance treatments
to check the build-up at these centres.
The value of preventive measures is fully realised, and where practicable, structural and incidental
rat proofing was advised and combined with extermination measures. Unfortunately many of the
premises treated were beyond structural proofing against ship rat or alternately it entailed work
which could not be undertaken at the present time.
In assessing the overall results of the work for the last three years, it can be said that the density
of the rat population is in no measure comparable with that of several years ago. This is widened
by our surveys and remarks made by occupiers of premises.
In conclusion, the terms of the " Direction " have been complied with as far as practicable,
having regard to problems peculiar to the City, the character of infestations, and the types of property.