THE SHELLFISH INDUSTRY 311 



may be are liable to be taken into the stomachs of the 

 shellfish which feed on any small particles in the water, 

 and, though they are themselves unaffected, they may in 

 this manner become a medium for the dissemination of 

 typhoid and other pathogenic bacteria. Rigorous regula- 

 tions forbid the sale of polluted shellfish but the risk of 

 disease has been an important, and in the past, not un- 

 justified reason for the undoubted prejudice against the 

 use of shellfish as a food. 



The best preventive measure would undoubtedly be to 

 forbid the discharge of unpurified sewage in the neighbour- 

 hood of shellfish beds, but unfortunately this is quite 

 impracticable at the present time. The only alternative 

 is to purify the shellfish and this has been done with 

 striking success at Conway, where the extensive mussel 

 beds had led to the development of a considerable industry, 

 the collected mussels being sold to the large Midland towns. 

 After an adverse bacteriological report the sale of these 

 mussels was prohibited in 191 2 and many men were thrown 

 out of employment so that the Corporation of Conway started 

 investigations, later taken over by the Ministry of Fisheries, 

 in the hope of finding some method whereby mussels could 

 be purified. This has to be carried out under artificial 

 conditions and for this purpose large concrete tanks were 

 constructed and, after lengthy experiments, a simple but 

 eminently successful method of purification was devised. 

 The mussels, which are brought to the tanks in sacks by the 

 fishermen are spread two deep on wooden grids in the 

 bottom of shallow tanks, as shown" in Plate 111, and 

 thoroughly hosed so as to clean the outside of the shells. 

 Sea water, which has been sterilized by the addition of 

 chloride of lime, any free chloride being converted into 

 common salt by the action of sodium thiosulphate, is then 

 run in by gravity from storage tanks, and the mussels 



