B. COLI IN MARKET OYSTERS 303 



From market No. VI 39 oysters were examined. No colon bacilli 

 were found. The supply was evidently free from pollution. 



The oysters from markets Nos. VIII and IX showed no organisms 

 of the colon group. 



The oysters from market No. VII, although perhaps not showing 

 indications of serious pollution, seemd to be in a state of decomposi- 

 tion which would render them unsuitable for consumption. From 

 17 oysters, one organism of the colon group and 10 proteus forms 

 were isolated. The oysters were no doubt old, as indicated by the 

 fact that their shells were slightly open. The presence of proteus 

 forms probably shows that the oysters were undergoing decomposi- 

 tion, which view is further borne out by the putrid odor which accom- 

 panied them. 



From the results of the examination it seems likely that growth in 

 the closed arm of the fermentation tube, without gas formation, indi- 

 cates the aging of the oysters. The presence of proteus forms prob- 

 ably means old oysters. 



SUMMARY. 



1. Eleven organisms belonging to the colon group were isolated 

 from the 294 oysters examined. 



2. Colon bacilli were found in oysters from five markets out of a 

 total of nine. 



3. The presence of B. coli in so large a proportion of oysters from 

 market No. V seems to show that the oysters had been in contact with 

 sewage. A second lot of oysters from the same market, but from 

 another source, showed no evidence of pollution. 



4. Colon bacilli in so small a proportion of oysters in Chicago 

 markets would hardly indicate a widespread pollution, but a more 

 extended examination might show different results. 



5. The colon test seems to afford a valuable means for determining 

 the purity of a city oyster supply. 



It is not intended to present these facts as a complete study of the 

 oyster supply of Chicago, but simply to show the condition of oysters 

 from several of the most important markets in order to illustrate the 

 value of such a bacterial examination. 



