Blood cells. Light micrograph of red blood cells and three white blood cells (stained blue). Red blood cells (erythrocytes) are responsible for carrying oxygen around the body, and for carrying waste carbon dioxide to the lungs for exhalation. White blood cells (leucocytes) are part of the immune system, which protects the body from micro- organisms that can cause disease. The nucleus of one of the white blood cells is clearly seen. The nucleus is multi-lobed and the cell is called a neutrophil. Magnification: x2000 when printed 10cm wide.