322 SEWAGE AND ITS PURIFICATION 



there are difficulties in the way of the sterilization of sewage 

 effluents, but these I have dealt with in Chapter VIII. It 

 would appear that as, failing such sterilization, all sewage 

 outfalls must necessarily more or less contaminate shellfish, 

 watercress, or drinking-water below, either th-o sewage outfall 

 must be removed, or nothing in the contaminated area should 

 be offered for internal consumption without purification. 



A bacteriological examination associated with topographical 

 evidence may even be misleading, as there are no doubt many cases 

 daily in which temporary pollution of a fishery or oyster laying 

 may take place by, say, faecal discharge from closets on board a 

 ship, and there is little evidence at present as to distance, time, 

 dilution, tides, and other factors which determine the possibility 

 of infection of shellfish by estuary waters. 



In a report by Dr. Houston to the Commission,^ a careful 

 investigation of over i,ooo oysters, from various layings through- 

 out the country, shows that nearly all contained B. coli communis 

 or closely allied organisms. It cannot be too widely known 

 that the Commission are clearly of the opinion that the mere 

 presence of B. coli microbes in an oyster does not justify its 

 condemnation. 



With regard to foreign shellfish, the Commissioners are 

 satisfied that in the interests of public health some safeguards 

 are necessary in connection with their importation and sale. A 

 suggestion was made that all consignments of foreign shellfish 

 should be required to be relaid for some period, in approved 

 waters, before being sold to the public. The Commissioners 

 doubt if such a requirement could be justified in the case of all 

 foreign shellfish. For the present, they think that it would be 

 a sufficient precaution to require a guarantee on the part of 

 each Government concerned that all oysters, or other shellfish, 

 imported into this country for human consumption had been 

 procured from localities where they were not liable to be 

 contaminated by sewage or other objectionable filth. 



Watercress, being at times almost immersed, may become 

 coated with polluted lime-crusts and not be easily cleaned by 

 washing. The London County Council's report of February 7, 

 1905, on watercress beds supplying London, concludes that, 

 " having in view the extent to which careful washing eliminates 

 impurity, it may be assumed that there is under existing cir- 



^ Fourth Report, 1904, vol. iii. 



