METALLIC STAINS 211 



also to coloration by the brown pyroligncous acid ; for Hermann 

 has obtained the same stain with sublimate material, or alcohol 

 material {op. cit., i, 1891 [18!)*2]. p. 7). ) 



Lee found this gives nmch better results than the pure 

 osmic acid process, but not the best possible. Lee proceeded as 

 follows : 



Hermann or Flemming material is brought in bulk, directly 

 after fixing, into a weak aqueous solution of pyrogallol. The 

 tissues may remain in it for twenty-four hoiu's, but for small 

 objects an hour or less is sufficient. An alcoholic solution of 

 pyrogallol may be taken if desired. Rawitz {Lehrbuch, p. 00) 

 takes 20 per cent, aqueous sol. of tannin. 



There is thus obtained a black stain, which is at the same time 

 a plasma stain and a nuclear stain, chromatin being so far stained 

 that it is not necessary to have recourse afterwards to a special 

 chromatin stain. With Invertebrates it sometimes gives very 

 elegant differentiations of nervous tissue. It is a very easy 

 method, and if pyrogallol be used a very safe one (with pyro- 

 ligncous acid not so safe). 



If it be desired to add a chromatin stain, Lee recommended 

 safranin (stain very strongly, twenty-four hours at least, and 

 start the extraction with acid alcohol). 



This method has been attributed to von Maehrenthal. See also 

 under " Nervous System " modifications of this method by Azoulay 

 and Heller and Gumpertz ; also one by Kolossow (Zeit. iviss. Mik., 

 ix, 1892, p. 38, and ix, 1893, p. 316). 



414. Perchloride of Iron. This reagent, introduced by Polaillon 

 (Journ. de VAnat., iii, 1866, p. 43), sometimes gives useful results, 

 especially in the study of peripheral nerve-ganglia, in which it stains 

 the nervous tissue alone, the connective tissue remaining colourless. 



The HoGGANS proceed as follows {Journ. Qiiekett Club, 1876 ; Journ. 

 Roy. Mic. Sac, ii, 1879, p. 358) : The tissue (having been first fixed 

 with silver nitrate, which is somewhat reduced by a short exposure to 

 diffused light) is dehydrated in alcohol, and treated for a few minutes 

 with 2 per cent, solution of perchloride of iron in spirit ; then with a 

 2 per cent, solution of pyrogallic acid in spirit, and in a few minutes 

 more, according to the depth of tint required, may be washed in water 

 and mounted in glycerin. 



FoL fixes in perchloride (§ 85) and treats for twenty-four hours with 

 alcohol containing a trace of gallic acid. 



Polaillon {loc. cit.) reduces in tannic acid. 



The method is not applicable to chromic objects. 



GoLODETZ and Unna {Monats. prakt. Derm., xlviii, 1909, p. 153). 

 put sections of skin for five minutes into fresh mixture of 1 per cent, 

 perchloride of iron and 1 per cent. sol. of ferricyanide of potassium. 

 See also Unna and Golodetz, ibid., xlix, 1909, p. 97. 



Roosevelt {Med. Rec., ii, 1887, p. 84 ; Journ. Roy. Mic. Soc., 1888, 

 p. 157) employs a stain composed of 20 drops of saturated solution of 

 iron sulphate, 30 grm. water, and 15 to 20 drops pjrogaliic acid. 



415. Palladium Chloride (see Sciiulze, § 82). Prussian Blue (see 

 Leber, Arch. Ophthalm., xiv, p. 300 ; Ranvier, Traite, p. 108). Cupric 



