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PUBLIC HEALTH (IMPOETED MILK) REGULATIONS, 1926.
No importation of milk requiring action under these Regulations was reported
during the year.
PUBLIC HEALTH (PRESERVATIVES, &c., IN FOOD) REGULATIONS,
1925 to 1927.
For action under these Regulations, reference is directed to the list of foodstuffs
submitted for analysis.
SHELLFISH.
Cleansing of Oysters.— On 2nd and 3rd August, at the invitation of Dr. R. W.
Dodgson, Director of the Shellfish Research Station of the Ministry of Agriculture
and Fisheries at Conway, your Medical Officer visited the Oyster Purification Station
at Brightlingsea. This is the first, and at present the only, station for the treatment
of oysters in this country.
The principle is the same as that employed for mussels at Conway, viz., to cleanse
the shells and then let the shellfish cleanse themselves by leaving them submerged
in a tank of sterile sea-water for a sufficient period. The main difference in practice
is that in the case of oysters in cold weather the water in the tank must be warmed
to about 56° F., whereas with mussels this refinement is not necessary.
The shellfish treated at Brightlingsea are Portuguese and American Blue Point
Oysters, which have been relaid in a tidal creek of the estuary of the River Colne.
At low water the oysters can be clearly seen on the mud banks in the creek, and it is
obvious that the layings are exposed to serious risk of sewage pollution.
The procedure of cleansing is as follows : The oysters are brought to the station
and laid not more than two deep on wooden gratings in concrete tanks (45 feet by
35 feet by 2 feet 6 inches). They are then hosed with powerful jets of sterilised
sea-water from a specially designed rake with which the double layer of oysters is
turned over so that all are thoroughly washed. The sea-water is sterilised by the
addition of the necessary amount of a solution of bleaching powder. The tanks are
sloped towards a channel at one end and the dirty water escapes through a
drain at the lowest point. The tank is then filled with sterilised sea-water and emptied
again, thus flushing away all the dirt that has been washed off the shells.
The next stage is to get the oysters themselves within their shells washed. This
is done by filling the tank with sterile sea-water, sufficient of a solution of sodium
thiosulphate being allowed to drip into the water as it enters the tank to neutralise
any residual chlorine. The submerged oysters open and pass the sterile water through
their shells as they naturally do in breathing and feeding, thus washing themselves