Polynuclear basophil. Coloured Transmission Electron Micrograph (TEM) of a basophil white blood cell. This basophil has one bi-lobed nucleus (yellow, lower centre) and a second nucleus at upper left, hence it is known as a polynuclear basophil. Purple granules in the cell cytoplasm (green) contain the vasoactive substances heparin (a blood anticoagulant), histamine and the slow reacting substance of anaphylaxis (SRS-A). Basophils are the least common of the white blood cells, and their function is poorly understood. Magnification: x6,200 at 6x7cm size.