226 CHAPTER XVII. 



will only take the second stain in the case of negative im- 

 pregnation. 



Other Metallic Stains. 



374. Csmic Acid and Pyrogallol. This method was first 

 published by me in 1887 (La Cellule, iv, p. 110). It consists 

 in putting tissues that have been treated with osmic acid 

 into a weak solution of pyrogallol, in which they quickty 

 turn greenish black, sometimes much too much so. 



HERMANN (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 broAvn 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 : 



HERMANN or FLEMMING material is brought in lutl\ 

 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 (Lehrl/uch, 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 after- 

 wards to a special chromatin stain. With Invertebrates it 

 sometimes gives very elegant differentiations of nervous 

 tissue. It is a very ea*y 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), 



