NUCLEAR STAINS WITH COAL-TAR PYKS. 171 



Employed in this way, with fresh unfixed tissues, methyl 

 green is a pure chromatin stain, in the sense of being a pre- 

 cise colour reagent for chromatin. For in the nucleus it 

 stains nothing but chromosomes or chromatin elements; it 

 does not stain plasmatic nucleoli (unless indeed these contain 

 chromatin) , nor caryoplasm, nor achromatic filaments. Outside 

 the nucleus it stains some kinds of cytoplasm and some kinds 

 of formed material, especially glandular secretions (silk for 

 instance, and mucin). The chromatin elements are invariably 

 stained of a bright green (with the exception of the nuclei n 

 of the head of some spermatozoa), whilst extra-nuclear struc- 

 tures are in general stained in tones of blue or violet. But 

 this metachromatic reaction is probably due to the methyl- 

 violet impurity, and is not obtained with a chemically pure 

 methyl green. 



Staining is instantaneous overstating never occurs. The 

 solution is very penetrating, kills cells instantly without swel- 

 ling or other change of form, and preserves their forms for at 

 least some hours, so that it may be considered as a delicate 

 fixative. It may be combined without precipitating with 

 divers fixing or preserving agents. Osmic acid (of 0*1 to 1 

 per cent.) may be added to it, or it may be combined with 

 solution of RIPART and PETIT (this is an excellent medium for 

 washing out in and mounting in). 



Alcoholic solutions may also be used for staining. They 

 also should le acidulated ivith acetic acid. 



The stain does not keep easily. It is difficult to mount it 

 satisfactorily in balsam, because the colour does not resist 

 alcohol sufficiently (unless this be charged with the colour). 

 The resistance of the colour to alcohol is, however (at all 

 events if it be used in the EHKLICH-BIOKDI combination), con- 

 siderably increased by treating the sections for a few minutes 

 with tincture of iodine before staining (M. HEIDENHAIN). 



Of preparations mounted with excess of colour in the usual 

 aqueous media, I find the most fortunate only survive for a 

 few months. Dr. HEKKEGUY, however, writes to me that it 

 keeps well in BRUN'S glucose medium. 



It was first pointed out, I Relieve, by HESCHL (Wiener med. Woclienscln-., 

 2, 1879), that methyl green is a reagent for amyloid degeneration. His 

 observations were confirmed by CURSCHMANN (Vircliow's Arch., vol. 

 Ixxix, 1880, p. 556), who showed that it colours amyloid substance of an 



