CHAPTER XVII. 209 



pyrogallol, in which they quickly turn greenish black, sometimes 

 much too much so. 



HEKMANN (Arch. mik. Anat., xxxvii, 4, 1891, p. 570) put platino- 

 aceto-osmic material hardened in alcohol for twelve to eighteen 

 hours into raw pyroligneous acid. This acid ought (Ergebnisse der 

 Anat., ii, 1893, p. 28) to be as raw as possible, and to be of a dark 

 brown colour and evil-smelling. (The stain obtained in this way is 

 not due to a mere reduction of the osmic acid, but also to coloration 

 by the brown pyroligneous acid ; for HERMANN has obtained the 

 same stain with sublimate material, or alcohol material (op. cit., i, 

 1891 [1892], p. 7). 



I find this gives much better results than the pure osmic acid 

 process, but not the best possible. I now proceed as follows : 



HEKMANN 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 hours, but for small objects an hour or 

 less is sufficient. An alcoholic solution of pyrogallol may be taken 

 if desired. RAWITZ (Lehrbuch, p. 60) 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 differentia- 

 tions of nervous tissue. It is a very easy method, and if pyrogallol 

 be used a very safe one (with pyroligneous acid not so safe). 



If it be desired to add a chromatin stain, 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. See also 

 under " Nervous System " modifications of this method by AZOULAY 

 and HELLER and GUMPERTZ ; also one by KOLOSSOW (Zeit. wiss. Mik., 

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



375. Perehloride 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. Quekett Club, 1876; Journ. 

 Boy. 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 ; 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. 



M. 14 



