when more than three dilutions are used in a decimal series of dilution, use the following guidelines to dilutions and refer to table 9221:IV. Several illustrative examples A through of combinations 0f positive are shown in table 9221:V. First, remove the highest dilution (smallest sample volume) if it has all negative tubes and at least one remaining dilution has a negative tube. Next, remove the lowest dilution (largest sample volume) if it has all positive tube. According to these guideline, the three dilutions in example a are selected by removal of the highest (0.001-ml) and the lowest (10-ml) dilutions.