Caption

Blood clot. Coloured scanning electron micrograph of erythrocytes, or red blood cells, tangled in fibrin. Fibrin is the insoluble form of the protein fibrinogen, a coagulation factor found in solution in blood plasma. Fibrinogen is converted to fibrin when acted upon by the enzyme thromboplastin. Fibrin forms a fibrous meshwork, the basis of a blood clot, which is the essential mechanism for the arrest of bleeding. Red blood cells contain the pigment haemoglobin, the main function of which is to transport oxygen around the body. Magnification: x2800 at 5x7cm size.