EXAMINATION OF SHELLFISH 259 



Determination of Bacteria of the Bacillus Coli Group. 

 The quantitative determination of the presence of B. coli 

 shall be in accordance with the following procedure: 



Measured quantities (i.o, o.i, o.oi c.c., etc., or their 

 equivalents in dilutions) of the shell water of each of 5 

 oysters selected from the dozen, shall be placed in fer- 

 mentation tubes containing lactose peptone bile, prepared 

 according to the method recommended by the Committee 

 on Standard Methods of Water Analysis. These shall be 

 incubated for three days at 37 C., and the presence or 

 absence of gas noted daily. For all ordinary purposes of 

 routine work a development of from 10 to 85 per cent of 

 gas during this time period shall constitute a positive test 

 indicating a presumption of the presence of at least one 

 bacterium of the Bacillus coli group in the quantity of shell 

 water tested. But no final B. coli rating based on these 

 results shall be used for official approval or condemnation 

 unless positive confirmatory tests for the presence of organ- 

 isms of the B. coli group shall have been obtained from 

 the tube of highest or next highest dilution from each 

 oyster, showing the presence of gas. These confirmatory 

 tests shall be begun immediately upon noting the formation 

 of gas, and carried out in accordance with the procedure 

 recommended by the Committee on Standard Methods of 

 Water Analysis. 



Statement of Results. The results of the bacterial 

 counts shall be expressed as Number of Bacteria per c.c. 

 The results of the tests for B. coli shall be expressed either 

 in the form of the following arbitrary numerical system 

 to be known as " The American Public Health Association 

 Method of Rating Oysters for B. coli; or in Estimated 

 Number of Bacteria of the B. coli Group per c.c. of the 

 Sample." 



