SEA-FISHERIES LABORATORY. 361 



tide. To accommodate the flow when the valve is closed, 

 underground tanks, or culverts, have been constructed, 

 which contain the sewage while the flood tide lasts. 

 Whenever the state of the tide permits, these culverts are 

 regularly scoured by men to prevent the accumulation of 

 sludge. The tide, on the ebb, sets round Great Orme's 

 Head and out to sea, and the sewage is carried 

 in this direction. Mr. Little, Sanitary Inspector of 

 Llandudno, informs me that this course of the sewage can 

 actually be traced by observing the oily-looking appear- 

 ance of the water as it rises to the surface. The 

 Llandudno sewerage system appears to be remarkably 

 well designed. Of course it might be treated, but 

 in this case the necessity is not so strong. I do not 

 think, therefore, that it can reach Conway Estuary unless 

 very exceptionally, as, for instance, on the very last of 

 the ebb and with the driving force of a strong N.W. wind. 

 In any case, the dilution on the flowing tide would be so 

 enormous that appreciable pollution at Deganwy could 

 hardly occur as the result of Llandudno sewage. 



The estimated population of Llandudno is about 

 10,500, and, taking the water supply as 25 gallons per 

 head, the daily discharge of sewage is about 262,500 

 gallons. The sewage is untreated. 



Bacteriological Analyses. 



The methods followed were similar to those employed 

 in the analyses of the Morecambe mussels, except that in 

 the case of the Conway mussel a period of 20 hours only 

 elapsed between the inoculation and counting of the 

 primary plates; this because of the rapid growth of the 

 colonies. The samples were brought back to Liverpool 

 late at night and kept in ice for about 12 hours, when 

 they were examined. 



