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38
clean. They are left submerged overnight, and the next morning the tank is drained
and the oysters are again hosed to wash away everything they have excreted. Then
for a second time the tank is filled with sterile sea-water and the oysters remain
submerged for a second night. The tank is then drained, the oysters hosed and all
excreta flushed away.
The last stage is to give the oysters a shallow bath for one hour in sea-water
to which sufficient bleaching powder has been added to give two parts per million
of residual chlorine. In this bath the oysters do not open, the object being finally
to sterilise the shells. The oysters are then taken from the tank and may either be
packed at once in receptacles (bags or baskets) which have been sterilised by immersion
in water treated with bleaching powder so as to contain 10 parts per million of residual
chlorine, or they may be stored for not more than one week and not more than six
deep in sterile sea-water which is changed every day.
Each package of oysters leaving the station is sealed with a specially stamped
lead seal.
It was not anticipated that this treatment would remove all bacteria from the
oysters, but in fact samples taken up to the present have proved to be sterile.
The station is quite small and compact, yet it is capable of dealing with six million
oysters per annum. The plant comprises two outdoor treatment tanks for use in
summer and four smaller covered tanks for use in the winter, when it is necessary
to warm the water to about 56° P., the optimum temperature for the cleansing process.
There are in addition electric pumps for pumping the sea-water from the creek into
the storage tanks and also to give the necessary pressure for the hosing process.
There are four water-storage tanks, each holding 28,000 gallons of water and
alongside there is the boiler house for warming the water in the winter. The seawater
is sterilised by the addition of a solution of bleaching powder as it enters the
storage tanks.
A small storage tank, a tank for the sterilisation of receptacles and an office
are also provided. The whole area of the station is fenced and concreted, and everyone
who enters must walk through a pool of water to which bleaching powder has been
added. No smoking is permitted, mainly to discourage spitting.
The charge for purification is eightpence per hundred oysters, but if the station
was working to capacity the charge could be reduced to sixpence. However, even
eightpence per hundred does not seem to be an excessive price to pay for the certainty
that oysters are a clean and safe article of diet, and several fishermen remarked to
your Medical Officer that their only complaint was that they were placed at some
disadvantage in competition with others who gathered oysters from layings which
it was contended were equally polluted, but who were not obliged to cleanse their
oysters. Unfortunately, neither the retailers nor the general public yet realise the
advantage of the cleansing of shellfish, and there was therefore no special demand
for purified oysters.
It may be hoped that in the near future either public opinion or regulations of the
Ministry of Health will insist that all molluscan shellfish shall be cleansed by a satisfactory
method at an approved station before being sold for human consumption.
Under the Public Health (Cleansing of Shellfish) Act, 1932, Local Authorities have
power to provide tanks or other apparatus for the cleansing of shellfish (together
with all works and appliances necessary for the proper use thereof) and to make in
respect of the use of any tank or other apparatus so provided, such reasonable charges
as the Authority may determine.
Public Health (Shellfish) Regulations, 1934.
On 14th November the Court of Common Council resolved to make an Order
under the Public Health (Shellfish) Regulations, 1934, and subsequently copies of
the following Notice were sent to the Minister of Health and the Minister of Agriculture
and Fisheries, to the Kent and Essex Sea Fisheries Committee, to the Worshipful