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26
constructed depositors for lowering the bait into the chambers
and placing it on the benching were obtained.
After an interval of one day each manhole was again
opened to ascertain the 'takes' and so to judge the extent of
infestation. It will thus be seen on this preliminary procedure
582 operations were involved. Where 'takes' were found initial
treatment was given at a later date. This however, was done,
not only in those manholes where 'takes' had been recorded, but
in a number of others in the same vicinity to be sure of complete
success. Initial treatment consisted of each selected manhole
being pre-baited twice (with an interval of one day) with
inocuous bait to encourage feeding, followed by a third baiting
with poison (zinc phosphide). A fourth visit was made to record
'takes' of poison bait. 57 manholes were given initial treatment
(11 having actually given positive results on test baiting) and as
these involved 4 visits each, 228 operations were thereby necessary.
A few weeks later in the year manholes which showed
positives on the first initial treatment and others in the vicinity
were given a second treatment (arsenic) — termed the first maintenance
treatment. These numbered 40 involving 160 operations.
A second maintenance treatment was given in the case of 11
manholes at the end of the year. I have given these figures to
show that the work was by no means of a light character.
Over 12,000 circulars were delivered to householders and,
after visiting, 802 premises were found to be infested in various
degrees. Treatment consisted of laying pre-baits on four consecutive
days (except when this was done directly into holes etc,
when two pre-baits were considered sufficient) followed by a
poison baiting on the third or fifth day. A further visit had
subsequently to be made to collect any untaken poison baits.
The results of the treatment were carefully kept and the figures
give the following results:—
Cleared on first treatment 691
Cleared on second treatment 85
Cleared on third treatment 26
The number of individual visits made was 6,067.
One indication of the success achieved was that during
the progress of operations many casual complaints were received
from sub-districts which had not been reached but very few
came from those areas which had received comprehensive
treatment.