20 SHELLFISH CONTAMINATION FROM SEWAGE-POLLUTED WATERS. 



The length of time required for this cleansing process to be thor- 

 oughly accomplished undoubtedly varies according to local condi- 

 tions. At least one month should always be allowed for this change 

 to take place, although an entire season would be preferable. 



Tables 5 and 6 show the sharp contrast between the bacteriological 

 findings on water and oysters from sanitary and insanitary grounds. 



TABLE 5. Bacteriological examination of water and shellfish collected from grounds 

 below the sewer shown in figure 1 . 



SHELLFISH. 



WATER. 



Extensive industries are being operated from the locality in which 

 these samples were taken, and the products are widely distributed. 

 The data given in Table 5 should be compared with the following 

 results obtained on shellfish and water taken from clean grounds: 



TABLE 6. Bacteriological examination of water and shellfish collected from clean grounds. 



SHELLFISH. 



WATER. 



FLOATING OYSTERS IN POLLUTED WATER. 

 INSPECTION DATA. 



When shellfish grounds are properly located with regard to sewage 

 disposal, it is not an uncommon practice to nullify the cleanly results 

 obtained by taking oysters from beds free from pollution and float- 



