Add 1 ml of sterile water  to the culture slant. If growth is confluent, puncture the medium with a Pasteur pipette  to allow contact of the water with the medium

Place the tube horizontally  so the fluid covers the entire surface of the medium

Allow 30 minutes for the extraction of niacin. The extraction time may be longer if the culture has few colonies

Raise the  slants upright for 5 minutes to allow the fluid to drain to the bottom

Remove 0.5ml of  the fluid extract to a clean screwcap tube

Sequentially add 0.5ml of the 4% aniline solution and 0.5ml of 10% cyanogen bromide

Close the tubes  and observe the solution for the formation of a yellow colour (= positive result) within 5 minutes. The yellow colour appears as a ring at the interface of the two reagents, or if the tube is shaken, as a yellow column of liquid

Add 2-3 ml of  4% NaOH to each tube and discard