SEA-FISHERIES LABORATORY. 145 



glass specimen cylinders of about 6 litres capacity were used 

 as tanks. It was thought, during the Piel experiments, that 

 the mussels opened their shells more freely in the dark than in 

 full daylight, so these glass jars were covered with black paper 

 and were fitted with cardboard lids. A solution of chlorine 

 in water was made as before, the strength of this was 

 determined, and it was diluted to a convenient concentration. 

 Titrations of the chlorine solution, and of the thiosulphate 

 standard solution, were made immediately before each 

 experiment. 



A similar jar containing only sea- water was used as a 

 control on the chlorinated water jar. The latter contained 

 sea-water dosed with chlorine to the concentration of 5 per 

 million. Mussels which had been sent from Barrow Channel 

 were placed in each jar, and then a sample of the same lot of 

 mussels was examined. The results of this analysis were : — 



First Sampling. Original, untreated mussels. 

 /Plate 1, 76 red colonies. 

 „ 2, 78 

 „ 3, 58 

 4 49 

 „ 5, 138 

 Mean number of sewage bacteria per mussel = 3,990. 



Second Sampling. After one day in chlorinated sea-water. 

 /Plate 1, 19 red colonies. 

 ,, 2, 33 ,, 



,, 3, 19 ,, 



„ 4, 17 

 „ 5,42 

 Mean number of sewage bacteria per mussel = 1,300. 



Third Sampling. After one day in unchlorinated sea-water. 

 /Plate 1, 50 red colonies. 

 n A 5o ,, 



„ 3,50 

 „ 4, 56 

 „ 5,50 

 Mean number of sewage bacteria per mussel = 2,590. 



l/50th 

 mussel 



l/50th 

 mussel 



l/50th 

 mussel 



