SOURCES OF CONTAMINATION. 15 
Sugars: Gas in dextrose, lactose, and saccharose, usually from 
30 to 50 per cent, the ratio of CO, to H equals 1 to 2. Acidity vary- 
ing from 3 to 6 per cent. 
fiver han s solution: Indol always present, either marked or in 
trace. 
Nitrates: Usually present, generally marked reaction. 
Gelatin: Flat, whitish, irregular surface growth with filiform stab. 
Commonly a few gas bubbles were seen in depths of medium without 
liquefaction. 
Agelutination: Not determined. 
SOURCES OF CONTAMINATION. 
LOCATION OF OYSTER BEDS. 
The proper control and location of oyster beds in relation to public 
health should be a matter of great concern to those engaged in the 
industry. In selecting these it is not only essential that oystermen 
Fic. 1.—One of three main sewers emptying untreated sewage into the mouth of a river. This sewage 
combines with that from several other large cities and flows over extensive shellfish grounds. 
should consider the localities best adapted to the growth, flavor, 
size, and appearance of their oysters, but they must also consider 
the possibilities of sewage contamination. Close proximity to any 
habitation paves the way to possible pollution, and with the multi- 
plication of dwellings the chance of dangerous contamination 
increases. | 
Because of insanitary methods of sewage disposal large areas of 
once valuable oyster grounds are at the present time subjected to 
conditions which render the shellfish taken from them wholly unfit 
for food purposes. (See Tables 1, 2,3, and 4.) On the other hand, it 
will be observed that the investigations show extensive oyster layings 
to be free from serious contamination, yet in these very localities 
