Light micrograph of human red blood cells (erythrocytes), with two unidentified white blood cells (leucocytes) near the centre. The function of the erythrocytes is the distribution & transport of oxygen & carbon dioxide to & from the cells of the body. Surrounded by a thin elastic membrane, the whole of the interior is filled with haemoglobin, an iron-containing red pigment which has a good oxygen-carrying capacity. Erythrocytes have a biconcave disc shape & are flexible so that they can accommodate themselves to the smallest of capillaries. The function of the leucocytes is that of defense against disease. Magnification: x270 at 35mm size.