MS 33.1 



METAL STAINS 



575 



They may then be mounted in balsam in 

 the ordinary manner. 



It will be immediately apparent that 

 this method is both (juicker and simpler 

 than the method of Penfield; but it does 

 not give such certain results, nor does it 

 stain oligodendria except by an occasional 

 accident which cannot be forecast. In the 

 author's opinion it is less generally satis- 

 factory than Penfield's technique even 

 for the demonstration of microglia. 



33.1 Staining Solutions 



The solutions of diammino silver used 

 in these techniques are usually prepared 

 by precipitating silver nitrate with sodium 

 hydroxide and then adding ammonia drop 

 by drop until the precipitate is just redis- 

 solved. It is much better to have a faint 

 opalescence remain than to use too much 

 ammonia. Some authors (Fontana 1912, 

 Masson 1928, Gomori 1937) ' recommend 

 a second addition of a few drops of silver 

 nitrate solution to insure an excess of this 

 reagent; but see Gros-Schultze 1938 below, 

 in which an excess of ammonia is used. 

 Sodium hydroxide as the initial precipi- 

 tant is sometimes replaced by potassium 

 hydroxide (Foot 1927a, Gomori 1937), 

 sodium carbonate (Cajal 1925, del Rio- 

 Hortega 1917, 1921, 1923, and 1927), 

 lithium carbonate (Foot 1927b, Laidlaw 

 1929, del Rio-Hortega 1919), or potassium 



oxalate (Herrera 1932). Ammonia is used 

 to produce as well as to dissolve the 

 original precipitate by Fontana 1912, 

 Gros-Schultze 1938, Lillie 1948, Masson 

 1928, and Weil and Davenport 1933. Tri- 

 ethanolamine is used both as precipitant 

 and solvent by Zettnow 1891. Gomori 

 1936 used methenamine, and Herrera 1912 

 used ethylamine, for the same purpose. 



Most of the solutions contain radicals 

 derived from the original silver nitrate as 

 well as from the precipitant and solvent. 

 On the contrary, the precijjitate is washed 

 after either filtration or decantation in the 

 formulas of Foot 1927b, Jalowy 1937, 

 Landlaw 1929, and del Rio-Hortega 1916 

 and 1921. 



The result of all this is of course to pro- 

 vide solutions of diammino silver of 

 various strengths and with various im- 

 purities. The table below summarizes the 

 solutions recommended, hsting (1) grams 

 of silver per liter, (2) reagent used to pro- 

 duce the original precipitate, and (3) re- 

 agent used to dissolve this precipitate. 

 Many of these solutions may appear to be 

 identical, but most authors are insistent 

 that the staining solution must be pre- 

 pared by the method and in the concentra- 

 tion which they recommend. The original 

 specifications are therefore given immedi- 

 ately following this table. For the sake of 

 uniformity each formula has been ad- 

 justed to a final volume of 100. 



SUMMARY OF DIAMMINO SILVER STAINING SOLUTIONS 



> Literature references to the authors cited in this and the next two paragraphs and in the table which follows 

 are given in the descriptions of the preparation of the solutions. 



