B. COLI IN MARKET OYSTERS 301 



gas formed in the tube after 48 hours at 37 C.,the test was considered 

 negative. However, if gas did form, a litmus lactose agar plate was 

 made as soon as possible, and after 24 hours agar tubes were inocu- 

 lated from the red colonies. The pure cultures were then studied. 

 Every fermentation tube not showing gas was examined at the end of 

 48 hours for growth in the closed arm, and a note made of the existing 

 condition. 



One c.c. of fluid from the oyster was thought to be sufficient to 

 inoculate the dextrose tube to show any gas-forming organisms 

 present in the oyster. In order to be more certain of that point, 

 several fermentation tubes were inoculated from one oyster, and the 

 tubes all showed the same results. The same process was repeated 

 on several occasions. 



As far as could be discovered, the majority of Chicago market 

 oysters come from Baltimore and New York; some come from Con- 

 necticut. The larger part of the supply is from Baltimore. 



Oysters from the following markets were examined: 



Market No. I. Large wholesale and retail market. Supplies oysters to many 

 of the smaller markets in Chicago. "Oysters from Baltimore." 



Market No. II. Wholesale and retail market. "Oysters from New York." 

 Market No. III. Wholesale and retail market. "Oysters from Baltimore." 

 Market No. IV. Large retail market. "Oysters from Connecticut." 

 Market No. V. Retail market. "Oysters from Baltimore." 

 Market No. VI. Retail market. "Oysters from New York." 

 Market No. VII. Retail market. "Oysters obtained from wholesale market 

 No. I." 



Market No. VIII. Retail market. "Oysters from wholesale market No. I." 

 Market No. IX. Retail market. "Oysters from New York." 



At numerous other markets visited it was found that the oysters were 

 obtained from some of the wholesale markets above mentioned. The 

 source of the oysters has been recorded just as the information was 

 received at the markets. 



The table following shows the results of the examination. 



As the figures in the table show, the oysters examined from market 

 No. I were free from any indication of sewage pollution. Only four 

 dextrose tubes from 63 oysters showed gas; from those tubes only 

 proteus forms were isolated. 



From market No. II 24 oysters were examined. Two dextrose 

 tubes showed gas. From one, an organism belonging to the colon 



