SEA-FISHERIES LABORATORY. 165 



show, then it may also be the case that a reduction in the 

 numbers of the micro-organisms contained in shellfish may- 

 be experienced as the result of keeping the sample for a day 

 or two after collection. I have obtained such a result in 

 at least one case. It is probable that micro-organisms 

 contained in the alimentary canal of the shellfish tend to be 

 extruded into the mantle cavity, and if the temperature rises, 

 or the mussels are kept too long, the water in the mantle cavity 

 may be lost by the opening of the shells. In such a case 

 the estimate of the bacteria per mussel may be less than it 

 ought to be. Obviously the samples ought to be stored in 

 small sterilised vessels which hold no more than the precise 

 number of shellfish which are to be examined, and the water 

 in the vessel ought to be added to the mixture, which is prepared 

 from the soft parts of the shellfish. It is as well that this 

 possibility of a reduction in the number of bacteria should 

 be considered in cases where apparently anomalous results 

 are obtained. 



The Barmouth purification experiment of 1915, referred 

 to on p. 140, is a case in point. Here we have to deal with 

 an estuarine area subject to pollution, as the chart published 

 in last year's report shows. In July of 1913 I visited the 

 estuary and made an inspection of the mussel beds and took 

 samples. These gave unequivocal evidence of most undesirable 

 pollution. A typical plate, made from l/50th part of a mussel 

 was photographed, and is reproduced as fig. 2 of Plate II in 

 the present report. In February of this year (1915) the 

 Fishery Officer at Aberdovey made the experiment to which 

 I refer above. The samples were sent to me by parcel post. 

 Fig. 1 of Plate II represents a typical plate made from l/50th 

 mussel, and the difference in the apparent pollution is very 

 marked. Such a degree of pollution as that represented by 

 fig. 1 I am inclined to regard as of little or no significance. 

 The question of the extent to which the mussels underwent 



