SEA-FISHERIES LABORATORY. 179 



market, were found to be sewage-polluted and to give 

 rise to the disease. In order to complete the case it is 

 necessary to exclude all other possibilities of contamina- 

 tion of the shell-fish between the date of gathering from 

 the mussel bed and that of sale and consumption in the 

 town. It is well known that shell-fish are sometimes 

 kept by the dealers for a considerable time before being 

 sold, and the possibility of contamination from sources 

 other than the natural habitat of the shell-fish must often 

 be a very real one. 



As the Conway mussels were getting a bad name in 

 some markets, and as the industry was an important one 

 locally and well worth attempting to save, the idea* 

 occurred to us of trying to induce the fishermen to 

 establish a practice of transplanting their mussels for 

 a few days into cleaner water before sending them to 

 market. So with the object of having more definite data 

 on which to base recommendations, Mr. Johnstone made 

 a series of experiments during 1908 to ascertain the 

 conditions under which polluted Conway mussels would 

 cleanse themselves from sewage bacteria when placed in 

 unpolluted water in the Conway neighbourhood. A 

 locality at the entrance to the estuary, on the Morfa 

 beach, was selected because the water there was found, 

 as the result of detailed bacteriological examination, to 

 be much more pure than that of the Conway Estuary in 

 general. Several lots of polluted mussels were then taken 

 from the worst parts of the Conway beds and were placed 

 in boxes fastened to the shore at the chosen part of 

 Morfa beach. Samples of these mussels were examined 

 bacteriologically at the beginning of the experiment, and 

 further samples were examined 4, 8 and 10 days after 



* The suggestion was also made by Dr. Klein in his Report to the 

 Fishmongers' Company. 



