140 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



Second sampling. Kelaid for three tides. 



i ;oKi.i (Plate 1, 13 red colonies, no colourless colonies. 

 l/25th J o k a 



mussel I " o a " a 



V 33 ^3 ° 33 " 33 33 



Mean number of sewage bacteria per mussel = 200. 



There was very little reduction in the number of contained 

 bacteria in these experiments, but that some reduction did 

 occur was quite certain. The mussels originally were not 

 polluted to a significant extent ; they were certainly quite 

 suitable as human food, in my opinion. The object of the 

 experiment was to test, in a preliminary way, the practicability 

 of utilising a floating movable tank for the purpose of containing 

 mussels undergoing cleansing, in such places where the nature 

 of the foreshore makes it difficult or expensive to construct 

 tanks or ponds, or other artificial enclosures. The experiments 

 are being repeated at other places on the Welsh coast. 



A further experiment of the same kind was made at 

 Barmouth in February, 1915. The same difficulties 

 presented themselves here as did at Aberdovey, that 

 is, the area of foreshore suitable for the construction 

 of a tidal cleansing pond or tank is very limited. The 

 floating tank used in the last experiment was, therefore, 

 again used in this one. It will be seen from Mr. Durlacher's 

 chart, published at p. 352 of last year's Report, that 

 the floats used for the drift experiments passed directly 

 in front of the inlet, called Aberamffra Harbour. But at 

 half flood-tide we might expect the sewage coming up from 

 the Harbour to be very greatly diluted, while the ebb-tide 

 would contain but little contaminating matter at any state ; 

 at all events the experiment was so arranged, and the tank 

 so moored that it dried, that is, it came aground, for about 

 four hours on each tide. Therefore, the first of the flood-tide, 

 which was the water most likely to be contaminated, did not 

 reach the mussels, while the last of the ebb-tide, water which 



