264 ELEMENTS OF WATER BACTERIOLOGY 



Clams are more likely to lose water during transportation 

 than oysters. It is therefore necessary to take greater 

 precautions to separate different samples of clams from 

 each other than in the case of oysters. 



In opening soft clams it has been found that if two 

 incisions are made through the mantle the shell water 

 may be poured out without opening the shell. 



Hard clams are more difficult to open, but if the shell 

 be struck over the dorsal muscle with a small hammer 

 an opening will be formed permitting the insertion of the 

 knife to cut the muscle. 



Sometimes clams and other shellfish contain too little 

 liquor to make all of the tests above described. This is 

 always the case when the shells are very small. Under 

 these conditions the water from two or more shellfish shall 

 be taken together and tested and considered as one. 



Standards of Interpretation. As in the case of water 

 it is neither practicable nor desirable to attempt to formulate 

 any hard and fast standard for passing or condemning 

 shellfish. It is very clear from the work carried out 

 by the English Commission, and at Lawrence, Boston, 

 Providence and New Haven in this country that shell- 

 fish from entirely unpolluted regions are free from colon 

 bacilli and that the proportion of positive tests for 

 these organisms increases with the increase in pollution. 

 Just where to draw the line, however, it is not easy to 

 say. According to Newlands and Ham (1910), the stand- 

 ards of permissible pollution adopted by various English 

 and American workers vary from a positive test in i 

 c.c. to a positive test in o.i c.c. of shell liquor. The 

 Bureau of Chemistry of the United States Department 

 of Agriculture condemns oysters sold in interstate com- 

 merce which show three positive tests out of five in o.i c.c. 

 portions, and the same standard has been adopted by the 

 Rhode Island Shell Fish Commission. 



