MULLENIX: EIGHTH CRANIAL NERVE. 223 



sodium hydroxide are added. This causes an immediate precipitate 

 of silver hydroxide.^ Ammonium hydroxide is now added in suf- 

 ficient quantity to dissolve the precipitate of silver oxide. It is neces- 

 sary to avoid more than the slightest excess of the solvent." This is 

 the solution which is commonly known as "Bielschowsky's fluid," 

 and may be designated as ammoniacal solution of silver oxide. If 

 it is allowed to stand for some time, a black precipitate is often depos- 

 ited, which Treadwell calls detonating silver. [AgNHgj^O. 



After the material has been treated with this fluid for a proper time 

 it is rinsed quickly and then transferred to a 20% solution of formalin, 

 as stated in a previous paragraph. In this solution, formaldehyde 

 is oxidized to formic acid and silver oxide, in the tissue, is reduced to 

 finely divided metallic silver, as indicated by the following equation : 



Ag3 O + C; 



In order to compare the probable efficiency of the Bielschowsky 

 method with that of Ramon y Cajal's process on chemical grounds, 

 I have carried out the following set of simple test-tube experiments, 

 with the results stated. 



1. Silver nitrate solution (2%) was treated with a 1% solution of 

 pyrogallic acid, at room temperature. The solution yielded after a 

 time a slight precipitate of finely divided metallic silver. The appli- 

 cation of gentle heat facilitated the reaction and caused a more copious 

 precipitate. 



1 The formation of this compound may be represented bj' the following equation: 

 AgNOj + NaOH = NaNOg + AgOH. 

 The silver hydroxide at once breaks down, forming water and dark brown siher oxide, 

 as follows: 



2AgOH = AgjO + HjO. 

 In h s treatise on Analytical Chemistry, Treadwell (:03) combines these two reactions 

 in the following equation; m 



2AgN0., + 2NaOH = AgsO + 2NaN03 + HgO. 

 ~ Dammer ('94) states that the chemical formula for the compound formed by this 

 process of solution is variable, and that the product may be represented by the formula 

 3Ag20.2NH3 or Ag20.NH3, or by some other formula. Treadwell (:03) represents the 

 reaction by the following equation: 



Ag^O + SNH^ + HjO = 2[AgNH3]OH. 

 Professor H. A. Torrey, of the Harvard Chemical Laboratory, who has had the kindness 

 to read this discussion of the chemical changes involved in silver impregnation, and who 

 has favored me with valuable suggestions and criticisms, tells me that the fluid obtained 

 by this process of solution behaves chemically as silver oxide in solution, and that for 

 practical purposes it may properly be so regarded. 



