140 METALLIC STAINS (IMPREGNATION METHODS). 



solution of the acid to 800 c.c. of the solution of the salt). 

 The object of the free acid is to decompose the precipitates 

 formed by the action of the silver salt on the chlorides, car- 

 bonates, and other substances existing in the tissues, leaving 

 only the albuminate, which is a more resistent compound. 



214. Silver Nitrate : Reduction. Reduction may be effected 

 in other media than distilled water. 



Y. KECKLINGHAUSEN washed his preparations in salt solution 

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

 path. Anat., xix, p. 451). Physiological salt solution (0*75 per 

 cent.) is commonly used for these washings. 



MULLER (Arch. f. path. Anat., xxxi, p. 110), after impregna- 

 tion 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 GIEEKE, in 

 Zeit.f. wiss. Mi~k., i, 1884, p. 396). 



EOUGET (Arch, de PhysioL, 1873, p. 603) reduces in glycerin. 



SATTLER (Arch. f. Mik. Anat., xxi, p. 672) exposes to the 

 light for a few minutes in water acidulated with acetic or 

 formic acid. THANHOFPER (Das Mikroskop., 1880) recom- 

 mends this method. He employs a 2 per cent, solution of 

 acetic acid. 



KRAUSE brings his preparations, after washing, 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 GIERKE, in Zeit. f. wiss. 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 ((TIERKE, 1. c.). 



JAKIMOVITCH (Journ. de VAnat., xxiii, 1888, p. 142 ; Journ. 

 Roy. 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 



