Light micrograph of a cross-section through a hedgehog's (Erinaceus europaeus) spine in dark field with ultraviolet (UV) excitation. The hedgehog's spine consists of the protein keratin (brown). Inside the spine there are gel-like substances that show a blue fluorescence in UV light. The section thickness is 30 micrometres. Magnification: x100 at a print width of 10 centimetres.