Coloured scanning electron micrograph (SEM) of a single white blood cell (leucocyte or leukocyte, white/blue) and red blood cells (erythrocytes, red) in a fibrin mesh (light brown). Erythrocytes contain the iron rich protein haemoglobin which binds oxygen. Erythrocytes transport oxygen from the lungs to the rest of the body and also remove carbon dioxide from the body by transporting it to the lungs where it is exhaled. Accounting for approximately 1% of blood, leukocytes are essential for good health and protect against illness and disease. They are made in the bone marrow and are stored in the blood and lymphatic system. When an area of the body comes under attack from bacteria, a virus or other foreign invaders that may threaten health, leukocytes will travel to the affected area to destroy the potential threat and prevent illness. Fibrin, a protein formed from fibrinogen during blood clotting, forms a mesh that disrupts the flow of blood thus preventing additional blood loss from the site of a wound. Magnification: x7000 when printed at 10cm wide