SEWAGE OUTFALLS AND DISCHARGE 327 



sterilization, require bacteriological attention, and that in the 

 examination for coli and enteritidis it is not the presence, but 

 the frequency or number of these organisms that is of most 

 import. 



Taken together, the precautions that lie in the hands of the 

 trader, and finally in those of the consumer, are the following : — 



1. Selection and maintenance of clean beds. — That good shell- 

 fish can be raised under such circumstances is proved by the 

 Report of the Local Government Board for Ireland, 1904, and 

 by evidence before the Royal Commission on Sewage, vol. ii., 

 1904, showing that many of the best brands come from localities 

 free from dangerous pollution. With regard to watercress, the 

 London County Council Report, already referred to, shows that 

 cress of the best quality can be grown under conditions to 

 which, from a public health point of view, no exception can be 

 taken (p. 7), and that the best beds were, generally speaking^ 

 found on a bottom of hard clean gravel : such beds are regularly 

 cleansed, and in some cases a light dressing of lime is used at 

 each cleansing in order to destroy organisms deemed to be 

 injurious (p. 6). 



2. Relaying of shellfish in purer water. — Although in common 

 use, and recommended by a large number of witnesses before 

 the Royal Commissioners, the purifying value of this practice 

 was defined in the Report as ''at present uncertain." Referring 

 to the work of Herdman, Boyce, and Klein, it was said^ that 

 ''judged from these experiments it would seem that polluted 

 oysters placed in approved waters might free themselves from 

 dangerous organisms in the course of a comparatively short 

 period [ten days to a month were mentioned], but as regards 

 cockles and mussels, relaying might be less effective." 



3. Sterilizing objectionable organisms in the beds themselves. — 

 Better precede by cleansing as far as possible. How chlorine, 

 acids, or copper can then be used I have indicated : the first 

 would probably be the cheapest, and at the seaside electrolysed 

 sea-water would readily be attainable (Chapter VIII.). 



It is customary to lay the oysters required for market in pits 

 at high-water mark, so that they shall be readily available for 

 transport. In these pits it is easy to add a sterilizing agent and 

 keep for a period of, as it were, quarantine, and to inspect them 

 as to objectionable organisms being killed. This would be 

 cheaper than attempting to sterilize the whole of the estuary or 



1 R. Comm. on Sewage, Fourth Report, vol. i., p. 40. 



