486 MEAT AND MEAT PRODUCTS 
The agar plates shall be incubated at 20° C. for three days and the 
colonies then counted. 
Determination of Bacteria of the Bacillus coli Group. The quanti- 
tative determination of the presence of B. col shall be in accordance 
with the following procedure: 
Measured quantities (1.0; 0.1; 0.01 ¢.c., etc., or their equivalents 
in dilutions) of the shell water of each of five oysters selected from the 
dozen, shall be placed in fermentation 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 B. colt group in the quantity of the 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 or 
organisms of the B. colz 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 Cubic Centimeter. The results 
for the tests for B. coli shall be expressed either in the form of the fol- 
lowing arbitrary numerical system to be known as “ The American 
Public Health Association Method of Rating Oysters for B. col; or in 
Estimated Number of Bacteria of the B. colt Group per Cubic Centi- 
meter of the Sample.” 
The American Public Health Association Method of Rating Oysters 
for B. coli.* The following values shall be assigned to the presence of 
bacteria of the B. colz group in each of the five oysters examined, these 
figures being the reciprocals of the greatest dilutions in which the test 
for B. cole was positive: 
If present in 1.0 c.c. but not in 0.1 ¢.c., a value of 1. 
If present in 0.1 ¢.c. but not in 0.01 ¢.c., a value of 10. 
If present in 0.01 c.c. but not in 0.001 ¢.c., a value of 100, ete. 
* Where the term B. coli is used, it refers in all cases to bacteria of the B. colt 
group and not to the specific prototype. 
