Application of the thiocarbohydrazide-osmium coating technique to scanning electron microscopy of the inner ear

The application of the thiocarbohydrazide-osmium coating technique to scanning electron microscopy of the inner ear is described. In this procedure specimens which have been prepared for electron microscopy (fixation in buffered glutaraldehyde or in Karnovsky's fixative followed by post fixation in osmium tetroxide) are twice exposed to solutions of thiocarbohydrazide and osmium tetroxide with water rinses in between each treatment. This method binds osmium to the specimen and so eliminates the need to coat the surface of the material with a layer of heavy metal. Initial observations indicate that this is a convenient and reliable method which is capable of yielding good results.