Caffeine crystals. Polarised light micrograph (PLM) of crystals of caffeine (1,3,7- trimethylxanthine). Caffeine stimulates the central nervous system increasing alertness and deferring fatigue. It is often contained in analgesic preparations with aspirin or codeine, and it is a diuretic. It occurs in coffee beans, tea leaves & cola nuts. Magnification: x20 at 6x7cm size. x30 at 4x5"~LANDSCAPE"