260 ELEMENTS OF WATER BACTERIOLOGY 



The American Public Health Association Method of Rating 

 Oysters Jor B. Coli* 



The following values shall be assigned to the presence 

 of bacteria of the B. coli group in each of the 5 oysters 

 examined, these figures being the reciprocals of the greatest 

 dilutions in which the test for B. coli was positive: 



If present in i.o c.c. but not in o.i c.c, a value of i. 



If present in o.i c.c. but not in o.oi c.c, a value of 10. 



If present in o.oi c.c, but not in o.ooi c.c, a value 



of 100, etc 



The sum of these values for the 5 oysters gives the total 



value for the sample and this figure shall be taken as the 



" rating for B. coli." 



The results shall be expressed in the following tabular 

 form: 



RESULTS OF TESTS FOR B. COLI IN DILUTIONS 

 INDICATED 



+ = presence of bacteria of the B. coli group in fermentation tube 

 test with lactose bile, 

 o = failure to demonstrate presence of bacteria of the B. coli group. 



Estimated Number of B. Coli per c.c. If the standard 

 B. coli rating above described is divided by 5, or, in general, 

 if the rating is divided by the number of oysters tested, 

 the result will be approximately the number of B. coli 



* Where the term B. coli is used, it refers in all cases to bacteria of 

 the B. coli group and not to the specific prototype. 



