DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY. DR JEREMY BURGESS / SCIENCE PHOTO LIBRARY.
False colour scanning electron micrograph (SEM) of stinging hairs along the main vein on the undersurface of a stinging nettle leaf, Urtica dioica. The stings are long hairs (short ones are harmless leaf hairs) with silicified tips which break off when the nettle is brushed against or stroked. The sting penetrates the skin, injecting a mixture of acetylcholine & histamine; the former a neurotransmitter substance normally produced at nerve terminals; the latter a chemical mediator normally produced by mast cells & responsible for many of the unpleasant symptoms of allergic reactions. The result is painful. Magnification: X50 (10x8), X 6 (35mm).
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