<prompt> In 4 split skin smears of a patient, 2 samples had 10 bacilli out of 100hpf and 2 samples with 1000 bacilli. Average bacteriological index would be3.54.55.56.5  <response>: RIDLEYS LOGARITHMIC SCALE FOR BACTERIAL INDEX Bacterial Bacteriological Index BI : Density of bacilli in smears, including both living and dead bacilli. Ridleys logarithmic scale : Based on the number of bacilli seen in an average High power microscopic field, using an oil-immersion objective 112 in or 2 mm When several smears are taken: Mean index is calculated. Score Description 6 Many clumps of bacilli in an average field over 1000 5 100-1000 bacilli in an average field 4 10-100 bacilli in an average field 3 10-100 bacilli in 10 fields 2 1-10 bacilli in 10 fields 1 1-10 bacilli in 100 fields In the given question, Two samples have 10 bacilli in 100hpf each1score, and Tw samples with 1000 bacilli in Average filed each 6 score BI 1166 4 3.5 Ref: Park 25th edition Pgno : 341-342 