Blood smear. Light micrograph showing human blood cells. Erythrocytes (red blood cells) are pink. They make up the majority of blood cells and carry oxygen to body tissues and carbon dioxide to the lungs. Two types of white blood cell (purple) can also be seen. They are, neutrophils (centre left and right) and a monocyte (upper left). White blood cells are part of the body's immune system. Neutrophils are the most abundant white blood cell. They engulf and digest invading bacteria. Monocytes are the largest white blood cell. They engulf and digest invading bacteria and cell debris. Magnification: x1000 when printed at 15cm wide.