EXAMINATION OF SHELLFISH 253 



sufficient time has elapsed, the oysters will have cleansed 

 themselves through their metabolic processes and 

 become entirely safe even for consumption in the raw 

 state. It is of considerable importance to determine 

 the length of time necessary for this self-purification 

 to take place. Obviously, from the commercial stand- 

 point it is desirable to make it as short as possible, 

 while from the sanitary standpoint it must be long 

 enough to insure a thorough and satisfactory removal 

 of all traces of polluted matter. Oyster beds which 

 are free from pollution or which are sufficiently good 

 for the re-laying for polluted oysters are difficult to 

 find and limited in areas because of their nearness to 

 sources of pollution. The investigations in question 

 were conducted by Phelps in the Providence River 

 and the upper part of Narragansett Bay. The oysters 

 were removed from heavily polluted regions and car- 

 ried to waters which were practically free from pollu- 

 tion, where they were planted. Examinations were 

 made from day to day in order to determine the length 

 of time that these particular oysters showed pollution 

 and it was found that within 4 days the organisms 

 of the colon type were practically all eliminated. 



It must be borne in mind that, if shellfish are care- 

 lessly opened and handled, they may suffer a considerable 

 additional pollution in the process, and may therefore 

 be much worse instead of better than when they were 

 taken. This is well brought out by the table on page 

 254, taken from a report by Stiles (1911) in which 

 shucked market oysters show much worse pollution 

 than market oysters in the shell. 



