SEA- FISHERIES LABORATORY. 141 



might also be polluted from the upper part of the Estuary, 

 did not come near them. 



Mussels were, therefore, collected from the bed of the 

 River Mawddach, between Aberamnra and the Railway Bridge, 

 the place usually fished, and these mussels were put into the 

 floating tank. The latter was moored at about half tide 

 level in Aberamffra Harbour. Samples were taken before 

 treatment, and after four and six tides, that is, after two and 

 three days. 



First sampling. The original, un-relaid mussels. 

 /Plate 1, 10 red colonies. 

 I/50th J „ 2,20 

 mussel I ,, 3, 8 ,, 



I „ 4, 6 

 Mean number of sewage bacteria per mussel = 440. 



Second Sampling. Relaid for four tides. 

 [Plate 1, 2 red colonies. 

 l/50th „ 2, 1 



mussel ,, 3, ,, 



I „ 4, 

 Mean number of sewage bacteria per mussel = 37. 



Third Sampling. Relaid for six tides. 

 (Plate 1, 1 red colony. 

 1 oOth I „ 2, 1 

 mussel | ,, 3, 1 ,, 



v „ 4, 

 Mean number of sewage bacteria per mussel = 37. 



That is, there was a reduction of sewage bacteria amounting 

 to about 92 % of the number originally contained in the 

 mussels. 



c. Experiments with water sterilised by 

 means of Chlorine. 



These natural difficulties are so great, in some places, 

 that the problem of naturally cleansing the mussels by exposure 

 to clean flood-tide water is insoluble ; or the cost of so treating 



