2.20 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 
re-laid on the former locality they would be under 
conditions enabling them to cleanse themselves. An 
experiment was therefore arranged in November of 1908. 
A quantity of mussels were raked from the bottom of the 
river almost underneath the Bridges (Sample I); another 
lot were raked from the river quite close up to Deganwy 
Sewer outfall (Sample IT); and a third quantity (Sample 
IIT) were taken from the bottom of mid-Channel between 
Deganwy and the Perch. These mussels were placed in 
fish boxes, each box being numbered, and the latter were 
then put down on the beach at Morfa. The boxes were 
surrounded by large stones to prevent them from being 
carried away by any unusual sea. It did blow hard 
during the progress of the experiment, but the boxes were 
not shifted. A man was engaged to “stand by” the 
mussels for a fortnight and prevent any interference with 
them. 
Samples were taken from each box before re-laying, 
and 50 mussels in all were examined individually. About 
Ol c.c. of the stomach juices (this is often as much ‘as can 
be obtained) was taken from each mussel and plated on 
Griinbaum’s neutral-red agar medium. ‘The number of 
red colonies was counted after 20 hours’ incubation at 
42° C. It was difficult, in some plates, to make a precise 
estimation of the numbers of colonies present, on account 
of their abundance, which led to fusion. It would have 
been better to adopt Houston’s method, but it was desired 
to investigate the individual, rather than the average 
pollution. The rounded numbers are estimated. 
