Renal medulla, light micrograph. 0.5 micrometre thick section of material embedded in plastic, stained with toluidine blue. The appearance of the collecting duct epithelium is seen in two sectional planes. At top, the cells have been sectioned along their longitudinal axis, appearing as a simple prismatic epithelium. The rest of the image is occupied by a tangentially sectioned collecting tube, which allows the polygonal contour of the epithelial cells to be visualized.