22 SHELLFISH CONTAMINATION FROM SEWAGE-POLLUTED WATERS. 
This process of treating oysters in the shell is variously described 
ee ‘feeding,’ ‘“‘freshening,”’ ‘‘ floating,” .‘ bleaching,”’ 
“drinking,” or “‘plumping.” By careful observation one can see 
oysters on ae floats open and close their shells, especially at the 
beginning of flood tide. The least sudden jar or meme shadow will 
cause them to close their shells immediately. 
The method of floating oysters as ordinarily practiced is not a 
true fattening process, but is only a means of increasing the bulk of 
the oyster by adding to the water content and gives it a lighter color. 
These changes are brought about by osmotic action caused by the 
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oyster being removed from comparatively salt water to a fresher 
medium, and they will not occur when the oyster is floated in water 
of the same saline content as that in which it was grown. Should 
the water in which these floats are placed be polluted with sewage 
Fie. 4.—T wo oyster floats anchored in the rear of oysterhouses. Privy vaults are located in the rear of 
these buildings, refuse being dumped direcily into the river. It is a crime punishable by $100 fine to 
float oysters in this river. An epidemic of typhoid occurred some years ago from oysters floated in 
this place. 
it is easy to see how the oyster may also become contaminated. 
Oysters may increase in bulk from 10 to 25 per cent or more when 
floated or when washed sufficiently long in running fresh water after 
shucking. ‘This variable increase in bulk depends upon the salinity 
of the water from which the oyster was previously removed, the 
length of time that the floating or washing is continued, a the 
Bieieie: of the water in which they are floated or washed. Shucked 
oysters from salt water increase in bulk the same as when in the shell 
if soaked in a plentiful supply of fresh water. On the other hand, 
plumped oysters, taken from ‘brackish water,’’ when placed in 
comparatively salt water, will decrease in bulk according to the 
saltiness of the water and previous treatment. 
In the course of this investigation many localities were visited 
where oyster floats were in operation, and in only a very few instances 
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