False-colour transmission electron micrograph (TEM) of a human mast cell isolated from connective tissue. In the cytoplasm of this cell are numerous granules (stained dark) which are released in response to inflammation or allergy. The granules contain several chemicals such as heparin, histamine & serotonin which are brought into service when the defence or immune system of the body is under attack through injury or allergy. Magnification: X 4570 at 35mm size. Originalis BW print P266/01M.