METALLIC STAINS (IMPREGNATION METHODS). 247 



precipitates formed by the action of the silver salt on the chlorides, carbo- 

 nates, and other substances existing in the tissues. 



341. Silver Nitrate : Reduction. Reduction may be effected 

 in other media than distilled water. 



v. RECKLINGHAUSKN washed his preparations in salt solution 

 before exposing them to the light in distilled water (Arch. f. 

 2>atlt. Anat., xix, p. 45]). Physiological salt solution (O75 

 per cent.) is commonly used for these washings. 



ML'LLEK (Arch. f. path. Anat.., xxxi, p. 110), after impreg- 

 nation by immersion for two or three minutes in a 1 per cent, 

 solution of nitrate of silver in the dark, adds to the solution 

 a small quantity of 1 per cent, solution of iodide of silver 

 (dissolved by the aid of a little iodide of potassium). After 

 being agitated in this mixture the preparations are washed 

 with distilled water, and exposed to the light for two days 

 in a 1 per cent, solution of nitrate of silver (see also GIERKE, 

 in Ze-it.f. wiss. M/'k., i, 1884, p. 396). 



ROUGET (Arc/i. da PliysioL, 1873, p. b'03) reduces in glyce- 

 rin. 



BATTLER (Arch. f. mik. Anat., xxi, p. 672) exposes to the 

 light for a few minutes in water acidulated with acetic or 

 formic acid. THANHOFKER (Da* Mikroskop, 1880) employs a 

 2 per cent, solution of acetic acid. 



KRAUSS brings his preparations, after washings, into a light 

 red solution of permanganate of potash. Reduction takes 

 place very quickly, even in the dark. The method does not 

 always succeed (see GIEKKE, in Zeit. f. wins. Mik., i, 1884, 

 p. 400). 



OPPITZ brings his preparations for two or three minutes 

 into a 0'25 or 0'50 per cent, solution of chloride of tin. 

 Reduction takes place very rapidly (GIERKK, loc. cit.}. 



JAKI.MOVITCH (Jo-urn, ch I' An at., xxiii, 1888, p. 142 ; Journ. 

 Itoif. Mic. Soc., 1889, p. 297) brings nerve preparations, as 

 soon as they have become of a dark brown colour, into a 

 mixture of formic acid 1 part, amyl alcohol 1 part, and water 

 100 parts. The objects exposed to the light in this mixture 

 for two or three days at first become brighter, a part of the 

 reduced silver being dissolved : hence the mixture must be 

 renewed from time to time. When all the silver has dissolved, 

 a darker colour is permanently assumed. The nerve- cells 

 are left in this mixture for five to seven days. 



