Light micrograph of human blood cells, showing numerous red cells (erythrocytes) and a single, monocyte. The red-staining erythrocytes are biconcave discs packed with haemoglobin that act as carriers of oxygen and carbon dioxide to & from tissues. Mature erythrocytes possess no nucleus or other organelles; these are lost during maturity. Monocytes are the largest of white blood cells, possessing large indented nuclei (purple) and cytoplasms with a "frosted-glass" appearance. They are highly motile, migrating into tissues (where they are termed macrophages) to scavenge debris & become involved in immune defences. Magnification: x400 at 35mm size.