Crenated red blood cells (erythrocytes) and a single white blood cell (leucocyte) in a fibrin mesh, coloured scanning electron micrograph (SEM). A blood clot is forming with many erythrocytes (red) and a single leucocyte (white/blue) becoming entangled in a fibrin net (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. However, these erythrocytes are crenated as depicted by the spiny knobs dispersed over the cell surface. This may be caused by hyperosmotic conditions or can be associated with the pathological condition uraemia. Leucocytes only account for about 1 per cent of blood but they are essential in protecting against illness and disease. Leucocytes will travel to areas infected by a virus or bacteria to destroy any potential threat and prevent illness. The blood cells here