SEWAGE CONTAMINATION OF OYSTEE BEDS. 235 



AXAI;TSIS OF OYSTERS FROM UNPOLLUTED SOURCES WHICH HAVE BEEN 

 PLACED FOR A TIME IN POLLUTED WATER. 



In connection with the above work, it has been interesting- to note 

 the effect produced on uncontaminated oysters by allowing them to 

 stand for a time in water highly charged with sewage matters. A 

 number of the oyster companies controlling beds in the lower river 

 and bay have docks and opening houses bordering on the Seekonk 

 River, in the neighborhood of the outlet of one of the small sewers 

 draining the east side of the city of Providence. At times the water 

 in the vicinit}^ of these wharves is filled with all sorts of organic 

 refuse, which passes down the river in a slow stream by the docks. 

 After the 03"sters have been dredged in the river below, they are 

 brought immediately to the cit}", and are very often dumped into 

 shallow cars moored close by the 03'ster houses, where they are allowed 

 to remain in the filthy river water until the openers are in need of new 

 material. They often remain in these cars from one to three days, 

 and thus have plenty of time to take in a good supply of sewage 

 bacteria, even though they were not infected when first brought to 

 the city. 



Two batches of oysters that had lain in floats in the Seekonk E,iver 

 for a time were subjected to the same tests used in this Avork on fresh 

 material. One batch of 5, dredged off Warwick Neck, had lain sixteen 

 hours in one of these floats. As has alread}' })een shown, Warwick 

 Neck oysters are not infected with B. coll or other sewage bacteria 

 when taken from the bods, but the juice of these 5 specimens gave 

 positive reactions for this organism; it was found in the intestines of 

 2 or 3 examined. The other batch was brought up from the Kicke- 

 muit River, whose beds also are free from sewage pollution and are 

 not infected Avith the colon bacillus. After these oysters had lain in 

 the car for two days, however, this organism was readil}" isolated 

 from the juice of all 5, though it v/as not found in the intestines of 

 any of them. Water samples taken in these cars also contained 

 B. coll. 



CONCLUSIONS. 



The sewage-contaminated area of the Providence River extends 

 dov/nstream from the outlet of the cit}- sewer at. Fields Point, a dis- 

 tance of about 5 miles. Below this area is a section about 2 miles 

 wide, extending from one side of the river to the other, in Avhich 

 B. coll is occasionally found. The tides and wind have considerable 

 effect upon this section, since evidence of sewage pollution has been 

 found only when samples were collected at very nearly low water. 



The waters of Providence River and Narragansett Bay from locali- 

 ties more than 8 miles distant from the principal sewers that discharge 

 into this basin do not contain sewage matters, and do not give positive 

 tests for B. coU. 



