PUBLIC FISHERIES FOR SHELLFISH 205 



If, therefore, polluted mussels are re-laid on the foreshore in such 

 a situation that they will only become covered by the sea after 

 the tide has been flowing for about three hours they will be bathed 

 in clean sea water. When the tide has ebbed for a similar period 

 the water again becomes seriously contaminated, since the depth 

 and width ol the channels diminish and the volume of inflowing 

 sewage is proportionally large. But by this time the re-laid mussels 

 are a-dry and are not exposed to pollution. 



When clean, germ-free sea water flows over mussels they open 

 their shells and a circulation is set up. Bacteria previously present in 

 the alimentary canal and shell cavity of the mussels are washed out 

 and the risk of re-infection is eliminated. The time required for 

 the cleansing purpose varies. In tanks musseh cleanse themselves 

 in pure sea water in twenty-four hours. A longer time is required 

 when mu"!S€ls are re-laid on the foreshore, since they are not con- 

 tinuously coveied with sea water, but two days are usually "-ufficient. 

 Re-laid mussels on the foreshore at Ovfrton in the estuary of the 

 Lune lost 90 per cent of the sewage bacteria present originally 

 after two days. No reasonable objection could then be made 

 to the use of these mussels as human food.^ 



It is no exaggeration to say that in a great number of reports of 

 the medical officers of health for our larger boroughs and urban 

 districts one constantly finds references to more or less isolated 

 cases of enteric fever alleged to be due to the consumption of shell- 

 fish. In some instances the number of cases is so large as to justify 

 the application of the term " epidemic " to the outbreak. It is 

 unnecessary to specify the exact places where such outbreaks have 

 occurred ; they are well known to students of public hygiene. The 

 difficulties in dealing with shellfish are possibly greater than is the 

 case with other articles of diet. The collection on the beds, the 

 consignment by rail, the handling at the wholesale inland market, 

 and the retail distribution by hawkers cannot be supervised by one 

 and the same authority. But there is one obvious means which 

 would naturally occur to anyone, to effectually prevent the sale of 

 contaminated shellfish, and that is to stop the gathering from beds 

 known to be polluted. Since the outbreaks of enteric at South- 

 ampton and Winchester^ following the consumption of oysters 



* One of the ablest summaries of the available information on this subject is 

 that by Johnstone. See 25rd Quarterly Report on the scientific work of the Lan- 

 cashire and Western Sea Fisheries District. " Report on Mussel Beds in Lancashire 

 and North Wales as Regards their Liability to Sewage Contamination." Liverpool, 

 C. Tinling and Co., 1913- 



* Report to the Local Government Board upon alleged Oyster-borne Enteric 

 Fever, and other illness following the Mayoral Banquets at Winchester and South- 

 ampton, and upon enteric fever occurring simultaneously elsewhere, and also 

 ascribed to Oysters, by H. T. Bulstrode. London, 1903. 



