Bone marrow. Light micrograph of a bone marrow smear showing red and white blood cells. The bone marrow makes blood cells by a process called haemopoiesis. The oxygen-transporting red blood cells (erythrocytes) make up most of the frame (grey structures). Stained more strongly are the infection- fighting white blood cells (leucocytes). Neutrophils, cells involved in inflammatory responses (pale with multilobed nuclei), can be seen at upper frame. At centre (dark with large nuclei) are monocytes that ingest bacteria and cell debris. At centre left (small dark) is a basophil that contains histamine. Magnification unknown.