sea-fisheries laboratory. 483 



Conclusions. 

 We must now attempt to draw some conclusions of 

 practical value from all this discussion. I take the 

 several mussel beds in the following order : — 



1. The Conway Estuary. 



It is now unnecessary to attempt to deduce any 

 practical conclusions with regard to this area. But since 

 we know more about it than any of the others, it may be 

 taken as a standard case with which the others may be 

 compared. We have then a narrow strip of water — about 

 ^rd of a mile wide and about 1-| miles in length. Few 

 brooks of any size open into this part of the estuary, but 

 the sewage from a population of over 6,000 persons does. 

 The pollution is mostly domestic sewage, as there are few 

 factories in the area discharging other kinds of effluent. 

 It is only land drainage to a slight extent, so that it is 

 reasonable to conclude that whatever pollution is 

 indicated by the mussels is derived from domestic refuse 

 and must contain human faecal matter. It is discharged 

 in the immediate vicinity of the mussels, so that, in the 

 conditions under which the industry is carried on, it is 

 possible for a bagful of mussels to have been bathed in 

 diluted sewage proceeding from houses and water-closets 

 only an hour or so previously, and to reach the consumer 

 a day later. 



The recent analytical results are given on p. 301. 

 It is there shown that the number of sewage bacteria 

 contained in the body of one mussel varies from 1,300 to 

 2,200. 



There is abundant epidemiological evidence, showing 

 that enteric fever has been transmitted by these mussels, 

 and even when we examine this evidence as critically as 

 possible, it must still carry considerable weight. 



