254 ELEMENTS OF WATER BACTERIOLOGY 



COMPARATIVE BACTERIOLOGICAL CONDITION OF MAR- 

 KET OYSTERS, SHUCKED AND IN THE SHELL 



(Stiles, 1911). 



Seasonal Variation of Bacteria in Oysters. It has 



been observed by Gorham (191 2) and others that the 

 examination of oysters from certain regions made in 

 the summer failed to agree with the similar analyses 

 from the same beds made in the winter. With the 

 advent of cold weather there seems to be a great 

 improvement in the sanitary quality, so that oysters 

 taken from beds in close proximity to the outfalls of 

 large sewers show in the colder months entire absence 

 of any evidence of contamination, judged solely by the 

 bacteriological data. Thus Gorham found in the sum- 

 mer of 1 910 that all oysters on the beds in the Prov- 

 idence and Warren Rivers and the upper part of Narra- 

 gansett Bay were so badly polluted by sewage as to 

 be unfit for iood. Colon bacilli were found in the 

 " shell water " of every oyster in amounts as small as 

 .01 of a cubic centimeter or less. Chemical and 

 bacteriological examination of the waters over these 



