Tissue processing for electron microscopy entailed that specimens from the right kidney of all rats were cut into small pieces of 1-2 mm3 thick, then immediately fixed in 3% glutraldehyde formol. Ultra thin sections of 0.6-0.8 µm in thickness were obtained from selected blocks, then mounted on copper grids and doubly stained with uranyl acetate and lead citrate. Sections were examined and photographed under electron microscope.