EXAMINATION OF SHELLFISH 251 



method was published in the Massachusetts State 

 Board of Health Report for 1905 (Clark, 1906). This 

 method consisted in the total counts of bacteria de- 

 veloping at 20° and 37° and the fermentation reaction 

 in dextrose broth. Experience indicated that it was 

 not merely necessary to examine the stomach contents 

 of the oysters but the " shell water " as well was sub- 

 jected to examination. With the advent of lactose bile 

 as a better medium for the development of B. coli 

 without interference with other types of bacteria, the 

 substitution of this medium for dextrose broth was 

 commonly made, and this is now one of the standard 

 media employed for the determination. 



It has been noted that the superiority of lactose 

 bile to dextrose broth is greatest in water examinations 

 when the water is most polluted. In the study of 

 shellfish the danger of overgrowths is even greater 

 than in polluted waters, since the organic matter in 

 the oyster and its surrounding shell water furnishes a 

 culture medium for many bacteria. Streptococci are 

 particularly abimdant. As pointed out in Chapter 

 IX, streptococci die out more rapidly than colon bacilli 

 in potable waters, but where organic matter is present 

 in abundance the former may survive the latter. 



We have compiled the table on page 252 from the 

 results of Clark (1906). In all cases except in that 

 of the shell water there is a considerable difference 

 between the dextrose fermentarion tests and the 

 colon isolations, indicating an overgrowth by strepto- 

 cocci and other forms, of colon bacilli originally 

 present. The B. sporogenes is also very frequently 



