A silver nitrate stain for nerve fibers and endings applicable to paraffin sections on the slide utilizes the properties of urea to accelerate the procedure and improve the specificity of the stain. After removal of the paraffin the sections are run through absolute, 95% and 80% alcohol and placed for 60-90 minutes at 5040°C. in: 1% aqueous silver nitrate, 100 ml.; urea, 20-30 g.; 1 g. mercuric cyanide and I g. picric acid in 100 ml. of distilled water, 1-3 drops. After the silver bath they are rinsed quickly in 2 changes of distilled water and reduced for 3-5 minutes at 25-30"C. in: water, 100 ml.; sodium sulfite, anhydrous, 10 g.; hydroquinone, 1-2 g.; urea, W 3 0 g. They are then washed thoroughly in 4-5 changes of distilled water, passed through graded alcohols into 80% alcohol and examined under the microscope. I f nerve fibers are not distinct, the sections are returned to the same urea-silver-nitrate bath for 1CL-15 minutes, rinsed, reduced, washed and dehydrated as before. This process may be repeated until staining is adequate; then they are dehydrated, cleared, and mounted.Nerve fibers show a color range from brown to black; nerve cells from yellow to brown; and the background, depending on the tYpe of tissue and its fixation, from yellow to light brown.Urea is one of the simplest non-electrolytes known to increase the solubility of coagulated proteins (Laportal); it also increases the diffusion rates of both electrolytes and non-electrolytes and facilitates their penetration into proteins, as shown by Bechhold and Ziegler? for gelatin and other proteins (Fischer and Sykes?). 'L.APOR.I A. >I. 1932. Beohachtungen iiber die Renatusierungen der Proteine. zBFc:rrrroLD. H.. and ZILGLER. J . 1906. Die Beeintlnssbarkeit der Diffusion 'FIXHER, M. H.. and SYKES. A. 1915. Cber die nicht-saure und nicht-al-Kolloidzschr.. 61, 376.in Gallerten.kalische Hydration cies Proteins.

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