SEA- FISHERIES LABORATORY. 119 



THE METHODS OF CLEANSING LIVING MUSSELS 

 FROM INGESTED SEWAGE BACTERIA. 



By James Johnstone, D.Sc. 

 (With a Chart and two Plates.) 



Contents. 



Introduction 119 



1. Identity of the micro-organisms inhabiting mussels 123 



2. Longevity of intestinal bacteria in sea- water 128 



3. Disappearance of intestinal bacteria from mussels undergoing 



self- cleansing, (a) experiments with sterile sea- water ; 

 (6) cleansing experiments in the open ; (c) cleansing by means 

 of chlorinated sea- water 133 



4. The effect of change of medium on the biological characters of 



intestinal bacteria 146 



5. Summary 148 



Appendices : — I, Reactions of the bacteria isolated ; II, Method of 

 graduation of the results of the experiments (2) ; III, On the 

 counts of colonies on the plates ; IV, On methods of sampling... 151 



Explanation of the chart and plates 167 



Introduction. 



Some time ago the Chairman of the Scientific Sub- 

 Committee requested me to make some investigations with 

 regard to practicable means of cleansing mussels from sewage 

 bacteria. Some experiments of this kind were made in the 

 past with respect to one definite locality — The Estuary of 

 the Conway — and favourable results were obtained. In these 

 experiments some boxes containing mussels were simply laid 

 down on the beach, being fixed so that the tide could not 

 wash them away. The idea underlying the experiments was 

 to expose polluted mussels to sea-water of the last two hours 

 or so of flood, and the first few hours of the ebb-stream. Flood- 

 stream water is practically unpolluted, and the first of the 

 ebb-stream water may also be regarded as unpolluted. In 

 these circumstances the mussels rapidly cleansed themselves 

 of about 90 % of the sewage bacteria originally contained 

 in them. The results were thus very satisfactory, but they 



