SOURCES OF CONTAMINATION. 



23 



were the sanitary conditions satisfactory. There are hundreds of 

 oyster floats in. use during the oyster season which are located in 

 waters of a more or less questionable nature, where the environment 

 makes contamination possible from one or more of the following 

 sources: From private or public sewers, privies, house drains, decay- 

 ing shell heaps, stable yards, chicken yards, dead animals, manure 

 piles on tilled land, refuse and garbage dumps of cities, etc. Figs. 

 2 to 10 and the data in Tables 7 and 8 show the facts on which this 

 statement is based. 



The wastes from the oyster boats are usually dumped directly over- 

 board into the water, which subsequently bathes the growing oysters. 

 If these boats are numerous it will be seen that the amount of pollu- 

 tion may be large. It is not a single source of pollution which neces- 

 sarily condemns the water as being in an unfit sanitary condition, 

 but it is the sum total of all the sources of contamination which 



FIG. 5. A closer view of the upper oyster floats shown in fig. 4. Note the pile of oysters in the float. Pic- 

 ture taken at low tide; about two hours later these same oysters were found in the adjoining oyster- 

 house ready for sale. Oysters drink best at the beginning of flood tide and are "plumpest " about one 

 or two hours afterwards. The main sewer of the city empties under the bridge above. 



gives the bacteriologist his final results. Oyster floats are nearly 

 always located in sheltered localities (see figs. 2-5), and in such places 

 the chances for contamination are greatest. The full sweep of the 

 ocean as it plays over the oyster beds under normal conditions does 

 not take place so readily where oyster floats are anchored, and thus 

 this factor of water purification is reduced in efficiency. 



It has been proved by observations and experiments made in the 

 course of this investigation that oysters when floated under the 

 usual conditions that is, in water that is only brackish deteriorate 

 more rapidly than the same stock unfloated. On this point Nelson 48 

 says that freshening oysters increases very rapidly the rate of weak- 

 ening and. decay, the life period being reduced one-half. This may 

 be due in part to the decrease in the salt content of the oyster, which 

 naturally acts as an antiseptic, or to the increased bacterial content 

 of the water in which the shellfish are floated. 



