8O SHELLFISH 



it is evident that cockles are frequently extensively polluted 

 and show sewage organisms in very large numbers. A number 

 of isolated examinations are recorded by Klein 1 . With cockles 

 taken from extensively polluted layings in the river Orwell, the 

 B. coli in the stomachs of the cockles varied from 4000 5000 per 

 cockle. On the other hand, with a batch of cockles taken from 

 layings far away from sewage contamination, only one of the 

 cockles contained a B. cotz-\ike organism and all were free from 

 true B. coli, streptococci or spores of B. enteritidis sporogenes. 



The writer has examined a large number of cockles taken 

 from various sources. Although some of them were personally 

 collected from sources well away from any considerable degree 

 of sewage contamination they all contained B. coli. The num- 

 bers present were, however, roughly in proportion to the extent 

 of the sewage contamination known to be present. 



The purification and self-purification of shellfish. 



The investigations of Klein, Herdman, Herdman and Boyce 

 have shown that when oysters are artificially inoculated by being 

 placed in water containing" very numerous typhoid bacilli, these 

 bacilli can be recovered from the oysters for from 10 to 18 days 

 subsequently, the actual period varying in the different experi- 

 ments. Herdman and Boyce 2 found that the bacilli did not 

 increase in the body or tissues of the oyster. When infected 

 oysters were washed in a stream of clean sea water there was 

 always a great diminution or total disappearance of the typhoid 

 bacillus in from one to seven days. 



Klein 3 in a later series of experiments showed that oysters 

 infected with very large numbers of typhoid bacilli cleaned 

 themselves, if placed in clear sea water, within a short period. 

 Klein's experiments showed that after eleven days the number 

 of typhoid bacilli were reduced enormously since they could not 

 be found when one-eighth part of an oyster was examined. 

 These results are not conclusive in regard to the total disappear- 

 ance of the typhoid bacilli. 



1 Oysters and Shell-fish, Report of the Fishmongers' Company, 1902-9. 



2 Thompson-Yates Laboratory Reports, 1898-9, vol. II. 



3 Experiments on Vitality of B. typhosus in Shell-fish, 1905. 



