In order to avoid fictitious accuracy and yet to express the numerical results by a method consistent with the precision of the work, the numbers of colonies of bacteria per cubic centimeter shall be recorded as follows:[212] Number of bacteria per cc. From 1 to 50 shall be recorded as found " 51 " 100 " " " to the nearest 5 " 101 " 250 " " " " " " 10 " 251 " 500 " " " " " " 25 " 501 " 1,000 " " " " " " 50 " 1,001 " 10,000 " " " " " " 100 " 10,001 " 50,000 " " " " " " 500 " 50,001 " 100,000 " " " " " " 1,000 " 100,001 " 500,000 " " " " " " 10,000 " 500,001 " 1,000,000 " " " " " " 50,000 " 1,000,001 " 10,000,000 " " " " " " 100,000 This applies to the gelatin count at 20° C. and to the agar count at 37° C. SUMMARY OF STEPS INVOLVED IN MAKING PRESUMPTIVE, PARTIALLY CONFIRMED AND COMPLETED TESTS FOR B. COLI. ────────────────────────────────────────────────────────────┬───────── Steps in procedure. │ Further │procedure │required. ────────────────────────────────────────────────────────────┼───────── I. Inoculate lactose broth fermentation tubes; incubate 24 │ hours at 37° C.; observe gas-formation in each tube. │ 1. Gas-formation, 10 per cent. or more; constitutes │ positive presumptive test. │ (a) For other than smallest portion of any sample │ showing gas at this time, and for all portions, │ including smallest, of sewage and raw water this│ test is sufficient. │None (b) For smallest gas-forming portion, except in │ examinations of sewage and raw water. │III 2. Gas-formation less than 10 per cent. in 24 hours; │ inconclusive. │II II. Incubate an additional 24 hours, making a total of 48 │ hours’ incubation; observe gas-formation. │ 1. Gas-formation, any amount; constitutes doubtful │ test, which must always be carried further. │III 2. No gas-formation in 48 hours; constitutes final │ negative test. │None III. Make plate from smallest gas-forming portion of sample │ under examination; incubate 18 to 24 hours; observe │ colonies. │ 1.