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31
Partial takes trebled those of 1959 and there was one
complete take compared with nil previously. Comparative figures
when zinc phosphide was used were:-
Partial takes 290
Complete takes 60
The Warfarin experiments although unconvincing are
worthy of continuation. The effect of sewer surcharges, etc. on
the use of captive polythene bags as opposed to free baiting with
zinc phosphide has still to be assessed. There is also the question
of the resistance of rodents to certain poisons to be considered.
ATMOSPHERIC POLLUTION
This work is carried out by Mr. E. Ulrich with two
assistants Miss B. P. Dimmock and Mr. J. A. Woodman. As in
previous years the Department's work in connection with air
pollution can be grouped under three main headings.
Investigation of Atmospheric Pollution
Cooperation with the Department of Scientific and Industrial
Research continued throughout the year. Daily readings of smoke
and sulphur dioxide concentration were taken from the continuous
filter at the Health Department and monthly analyses of measured
rainfall collected in the standard deposit gauge were also provided
for the Department of Scientific and Industrial Research.
Readings from the deposit gauge, together with further
information on sulphur activity in the air have also been taken and
passed on to the Department of Scientific and Industrial Research
since 1953 as part of the build-up of a picture of the distribution
of air pollution over the whole of the country. It is now known
that the information provided by the deposit gauge and the lead
peroxide candle is extremely localised in its application and should
only be taken as definitive of the degree of air pollution existing
close to that particular instrument.
The readings from any one such instrument cannot therefore
be taken as an indication of the pollution levels for the area and
even the average of readings from several instruments will give
only a very approximate figure. A further drawback is that the