312 THE SEAS 



are left in this water for one day. They quickly open their 

 shells and discharge the contents of their stomachs including 

 any bacteria they may contain, while at the same time 

 they take in sterilized water. This water is then run off 

 and the tank filled with fresh sterilized water for a similar 

 period to make sure that the mussels are thoroughly 

 cleansed internally. Again the water is run off and, last 

 of all, the shells are sterilized with chlorinated water, the 

 cleansed mussels being then packed in sterilized bags and 

 sent off to the markets. This system of cleansing was 

 begun on a commercial scale in 191 6, and has proved a 

 complete success, the flavour of the mussels is not impaired 

 while there have been no further complaints of pollution, 

 and the mussel fishery has regained its original importance. 

 As expenses have to be met by a fixed charge for each bag 

 of mussels cleansed, only the larger mussel fisheries can be 

 treated in this way owing to the expense of erecting the 

 cleansing tanks, and consequently many of the smaller 

 fisheries which have been condemned cannot be treated 

 in this way, but a second cleansing station has recently 

 been erected at Lympstone on the River Exe in Devon- 

 shire. Mussels are only collected during the winter, 

 and during the summer months the tanks are used 

 for experiments on the purification and breeding of 

 oysters. 



Oysters do not take in bacteria quite so readily as do 

 mussels, but when they are polluted are more difficult to 

 purify, owmg to the fact that unless the water is over a 

 certain temperature they refuse to open their shells and 

 so become sterilized internally. It is probably only a 

 question of time before a suitable method of purification 

 is devised when it will be possible with perfect safety to 

 eat oysters from many localities now banned on account 

 of pollution. The shellfish industries are in their infancy 



