Scanning electron micrograph of a blood clot on the underside of a sticking plaster that has been used to treat a razor blade cut. Red blood cells (shown in red) and thin fibres of the protein fibrin (beige) can be seen between the gauze fibres of the plaster (blue-grey). Fibrin is a protein formed from the conversion of clotting factors in the blood; the fibrin fibers trap blood cells and platelets to form a solid clot. This not only prevents further bleeding but also protects the open wound from infection.