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 datain 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® 
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. 
