68 TEANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



treating polluted mussels so that they may cleanse themselves 

 from sewage bacteria. The shellfish were subjected to the 

 cleansing action of a current of pure sea-water, and it was 

 found that they were practically freed from sewage bacteria 

 in 24 hours. Shellfish were also kept in standing pure 

 sea-water, when it was found that the cleansing process was 

 naturally slower, but that it might be accelerated by frequent 

 changes of water : two to three days was then found to be 

 the time that was necessary under these conditions. Shellfish 

 were also subjected to treatment by sea- water containing 

 chlorine. It has been known for some years that traces of 

 chlorine sufficed practically to sterilise drinking water, and a 

 commercial purification process of this nature has been in 

 use in connection with small drinking water installations. 

 The method is now going to be employed by the Conway Corpora- 

 tion, under the supervision of the Board of Agriculture and 

 Fisheries, for the purpose of purifying the polluted mussels 

 taken in the Conway Estuary. Dr. Johnstone found that 

 mussels live well in sea- water containing five parts per million 

 of chlorine, and could be cleansed from sewage bacteria by 

 three changes of sea-water so dosed with chlorine. Sea-water 

 containing sewage bacteria was sterilised by the addition of 

 one part of chlorine per million. The actual time required 

 for each change of water must, however, be worked out in the 

 actual commercial plant employed for the purpose. 



Mussels placed in rough enclosures on the foreshore at 

 about half-tide level also cleanse themselves from sewage 

 bacteria. Where enclosures cannot be made on account of 

 the nature of the foreshore, a removable floating tank was used 

 to store the mussels. Such experiments were made at Overton, 

 Sunderland Point and Glasson, all in Morecambe Bay, and at 

 Aberdovey and Barmouth in Cardigan Bay. These 

 experiments were all quite successful, since it was found that 

 a period of two to three days was enough for the process of 



