A revised tannin-osmium method for non-coated scanning electron microscope specimens.

Small blocks of the kidney and other organs were taken from adult rats, which had been perfused arterially with Ringer solution and with 0.1M phosphate buffer containing 2% glutaraldehyde (pH 7.4). The blocks were further fixed for 28hrs in 2% glutaraldehyde in a phosphate buffer (pH 7.4). The fixed spcimens were soaked for 16hrs in distilled water containing 2% arginine hydrochloride, 2% glycine, 2% sodium glutamate and 2% sucrose (pH 6.2), rinsed for 30min or more in distilled water, and immersed for 24hrs in 2% tannic acid in distilled water (pH 4.0). The specimens were then washed thoroughly in distilled water, stained for 6hrs in 2% osmium tetroxide and again washed thoroughly in distilled water. The specimens thus treated were dehydrated through a graded series of acetone, dried in air and observed, without any coating, under the scanning electron microscopes (JSM-2, JSM-U3) using an accelerating voltage of 25kV.