82 SHELLFISH 



contamination. In the creek of the estuary was a very large 

 oyster fattening ground. 



The polluted muds showed 10,000 to 100,000 B. coli per 

 gramme of mud where most polluted, decreasing very regularly 

 to 10 or less than 10 per gramme in the unpolluted creeks. The 

 number of streptococci showed similar and gradual diminutions 

 from 100 to 10,000 per gramme to less than 10 per gramme. 



The writer concluded that mud samples yield more reliable 

 bacteriological evidence of the degree of contamination of a tidal 

 river than either water or oyster samples. The latter only indi- 

 cate immediate and actually present pollution while mud samples 

 show evidence of past contamination. If the muds show a rela- 

 tively high purity they point to a safe fattening area for oysters. 



Data as to the intestinal bacteria in sea water over oysters is 

 given on pages 75 to 77. 



The bacteriological examination of sliellfish. 



A. Methods of collection and transmission. Care must be 

 taken to collect a representative sample and precise local par- 

 ticulars must be recorded. Shellfish should be collected from 

 different parts of the area as some parts may be much more 

 liable to contamination than others. The relationship of the 

 beds to the tide (if, as is usual, they are in tidal waters) must be 

 noted, particularly the extent to which the beds are covered or 

 uncovered by the tide. The neighbourhood and distances from 

 all sources of contamination, particularly sewer outfalls, must be 

 carefully recorded. 



The samples must be transmitted for examination without 

 delay and under conditions which do not allow of contamination 

 in transit. 



In the examination of consignments of shellfish collected 

 and brought into the market it is very desirable to obtain all 

 possible particulars in regard to the time since collection and the 

 intermediate conditions of storage. These particulars may not 

 be necessary for judgment as to the contamination or otherwise 

 of the particular samples, but they are necessary if the examina- 

 tion is to be used in any way as a guide to the condition of the 

 beds themselves. 



