260 CHAPTER XVIII. 



methods that I know of for the study of Nebenkerne. 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 pyroligneous acid not so safe). 

 Although, as said, this method enables one to dispense 

 with a special second chromatin stain, yet it is frequently 

 very advantageous to use one. I greatly recommend safranin 

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

 the extraction with acid alcohol). 



This method has been attributed to VON MAEHRENTHAL. A modification 

 of this method is said by AZOULAY to give a specific stain of the medullary 

 sheath of nerves; see his process under " Neurological Methods " in Part II. 

 See also a similar process for medullated nerve by HELLER and GUMPERTZ, 

 quoted Zeit.f. wiss. Mik., xii, 3, 1896, p. 385. 



The communications of KOLOSSOW (Zeit.f. wiss. Mik., ix, 1, 1892, p. 38, 

 and ix, 3, 1893, p. 316) do not appear to me to constitute a useful con- 

 tribution to the subject. 



362. Perchloride of Iron. This reagent, introduced by POLAILLON 

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

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

 tissue alone, the connective tissue remaining colourless. The method con- 

 sists in impregnating in perchloride of iron, and reducing in tannic, gallic, 

 or pyrogallic acid. 



The HOGGANS proceed as follows (Journ. Quekett Club, 1876; Journ. 

 Roy. Mic. Soc., 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. It is then treated 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 (see ante, 80) fixes in perchloride solution, and treats the prepara- 

 tions for twenty. four hours with alcohol containing a trace of gallic acid. 



POLAILLON (loc. cit.") reduces in tannic acid. 



This method is not applicable to chromic objects. 



I have found it useful in certain special cases. 



363. Pyrogallate of Iron (KOOSEVELT, Med. Rec., ii, 1817, p. 84 ; 

 Journ. Roy. Mic. Soc., 1888, p. 157). A stain composed of 20 drops of 

 saturated solution of iron sulphate, 30 grms. water, and 15 to 20 drops 

 pyrogallic acid. 



364. Palladium Chloride (see P. SCHULTZE, ante, 78). Prussian 

 Blue (see LEBER, Arch. f. Ophthalm., xiv, p. 300; EANVIER, Traite, 

 p. 108). Cupric Sulphate (see LEBER, ibid.). Lead Ohromate (see 



