CHAPTER XIII. 



H^MATEIN (HJEMATOXYLIN) STAINS. 



237. Introduction. Hcematoxylin is a dye extracted from log- 

 wood. It is a substance that oxidises very readily, thus becoming 

 converted into hcematein, or, as often happens, into other more 

 highly oxidised products. It appears to be now thoroughly well 

 established (see NIETZKJ, Chemie der organischen Fdrbstoffe, Berlin, 

 Springer, 1889, pp. 215217, and MAYEE, Mitth. Zool Stat. Neapel, 

 x, 1891, p. 170) that the colouring agent in solutions of log- 

 wood or haematoxylin is not the haematoxylin itself, but hsematein 

 formed in them (or, in some cases, one of the higher oxidation 

 products). 



Haematein is an acid body, a " colour acid " ( 201, 206). Sut>- 

 stantively employed, it is a very weak plasma stain. But combined 

 with appropriate mordants it becomes basic, and can be made to 

 give a powerful nuclear stain, or at the same time a nuclear and a 

 selective plasma stain. The mordants employed in histology are 

 aluminium, chrome, iron, copper, and (rarely) vanadium and 

 molybdenum. Aluminium and iron are the mordants most em- 

 ployed, the former furnishing lakes used for progressive staining of 

 material in bulk, the latter forming in most cases in the tissues a 

 lake that requires differentiation, and is only applicable to the 

 staining of sections. 



The presence of a sufficient amount of haematein in staining 

 solutions was formerly brought about by allowing solutions of 

 haematoxylin to oxidate spontaneously by exposure to air. The 

 change thus brought about in the solutions is known as " ripening/* 

 and until it has taken place the solutions are not fit to use for 

 staining. 



It was discovered by MAYER and UNNA independently (see MAYER 

 in Mitth. Zool. Stat. Neapel, x, 1891, pp. 170186 ; UNNA in Zeit. 

 wiss. MiL, viii, 1892, p. 483) that nothing is easier than to bring 

 about this change artificially ; all that is necessary being, for in- 

 stance, to add to a solution of haematoxylin containing alum a little 

 neutralised solution of peroxide of hydrogen or other powerful 



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