SOURCES OF CONTAMINATION. 



15 



Sugars: Gas in dextrose, lactose, and saccharose, usually from 

 30 to 50 per cent, the ratio of CO 2 to II equals 1 to 2. Acidity vary- 

 ing from 3 to 6 per cent. 



Dunham'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. 



Agglutination: 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 



FIG. 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 



