If no dilutions has all positive tubes (Example F), select the lowest two dilutions, corresponding to 10 and 1 ml sample. For the third dilution. Add the number of positive tubes in the remaining dilutions (0.1, 0.01, and 0.001 ml sample), to yield a final combination 4-3-2. If the third dilution is assigned more than five positive tubes, than the selected combination will not be in table 9221: IV