86 SHELLFISH CONTAMINATION FROM SEWAGE-POLLUTED WATERS. 
INSUFFICIENT COOLING. 
The proper cooling and subsequent refrigeration of any perishable 
food product is highly essential to prevent rapid decay from bacterial 
activity. The results obtained in a series of experiments on the keep- 
ing qualities of oysters demonstrate that the proper refrigeration of 
shucked oysters is necessary to retard deterioration. Even when 
such oysters are kept at low temperatures above the freezing point 
there is some bacterial development taking place, but this is reduced 
to the minimum by a plentiful supply of ice. 
SOURING DUE TO AGE. 
The souring of oysters may occur because of the length of time 
they are allowed to stand after shucking. Such oysters may have 
Fic. 14.—Various types of containers for shipping oysters, as used by the trade. 
contained but few organisms originally when freshly opened, but 
because of age alone they become unfit for use. There are always 
enough bacteria present in oysters even when opened under the best 
of sanitary conditions to cause spoilage after a certain interval of 
standing. This length of time will depend upon the number and kind 
of bacteria present and the temperature at which the oysters are 
stored. This fact is well illustrated in fig. 15, showing the results of 
two methods of keeping opened oysters. 
Shucked oysters are best when freshly opened, and they should be 
consumed at the earliest possible moment after shucking, although 
oysters grown on sanitary beds and handled under proper conditions 
remain edible for several weeks, when unshucked, but their quality 
does not improve with the length of time out of the shell. Illness 
of a serious nature may result from eating stale shellfish. 
