Polarised light micrograph of crystals of nicotinamide (niacinamide), one of the B group of vitamins. Nicotinamide is the amide of nicotinic acid (niacin) and is interchangeable with it, both forms of the vitamin being equally active. Good sources are meat, yeast extract and some cereals. A deficiency of the vitamin leads to the disease pellagra. Magnification: x60 at 35mm size.