Scanning electron micrograph (SEM) of crystals of pure anhydrous cholesterol precipitated from ethanol. Cholesterol is a sterol, a waxy, fat-like material synthesised by all animal cells. It is an essential constituent of the cell membrane, a precursor to the formation of sex hormones and the source of bile salts. A third of body cholesterol is produced in the liver. Its excretion, directly or as bile salts, is the sole responsiblity of the liver. Body cholesterol is added to by dietary cholesterol, mainly from meat and dairy products. High levels are associated with atheroma (furring of the arteries) and coronary heart disease. Mag: X 115 at 35mm size. Original is A600/214.