SHELLFISH $7 



Penryn oysters. 



B. coll test. 



i out of 25 (4%) contained 100 B. coli or coli-like microbes per oyster. 

 13 > (5*%) . ioo 

 ii (44%) , 10,000 



B. enteritidis sporogenes test. 



3 out of 25 (t2/ ) contained 10 spores of B. enteritidis sporogenes per oyster. 

 20 (So/ ) 100 



2 (8%) 1000 



These three typical groups of results show that B. coli and 

 B. enteritidis sporogenes are present in oysters in amounts roughly 

 proportionate to the extent of their pollution with sewage. In 

 the same way as for water supplies it is not the presence of these 

 organisms which has to be considered but their relative abun- 

 dance. Even oysters from reasonably pure sources will frequently 

 show some B. coli and it is only deep sea oysters which are quite 

 free. These general conclusions are in accord with the work of 

 Klein, McWeeney, Clark and Gage, etc. 



As regards standards for comparative purposes Houston 1 has 

 given the very useful classification contained in the table on p. 78. 



The bacteriology of mussels in relation to sewage pollution. 



Very few data seem to be available as to the bacteriological 

 content of mussels from perfectly pure surroundings. Some of 

 the earlier workers (e.g. Herdman and Boyce) found B. coli 

 organisms to be usually absent but these results were probably 

 due to incomplete examinations and are not in accord with later 

 experience. 



Johnstone 2 from extensive work states : " my own experience 

 has been that no sample of ten or more mussels can be 

 examined without finding Bacilhis coli y or at least some organ- 

 isms resembling this form." Even with mussels examined well 

 away from considerable sewage contamination (such as at some 

 beds in Morecambe Bay) B. coli were numerous. In the case of 

 ten mussels from this source the number of intestinal bacteria 

 isolated from about 0*2 c.c, of the stomach juices varied from 

 3 to 65, average 24*2. 



1 Jo urn. oj Hygiene, 1904, vol. IV, p. 182. 



2 Journ. of Hygiene, 1910, vol. ix, p. 412. 



