CHAPTER XIII. 

 HAMATE IN (H^IMATOXYLIN) STAINS. 



232. Theory of Haematoxylin Staining It appears to be now 

 thoroughly well established (see NIETZKI, Chemie der organ- 

 ischen F&rb*toffe 3 Berlin, Springer, 1889, pp. 215 217, and 

 MAYER, Mitth. Zool. Stat. Neapel, x, 1891, p. 170) that the 

 active colouring principle of the usual histological staining 

 solutions is hsematein, a product of the oxidation of their 

 contained haematoxylin by means of the air to which they 

 are exposed (see MAYER, " Ueber das Farben mit Hamatoxy- 

 lin" in Mitth. a. d. Zool. Station zu Neupel, Bd. x, Heft 1, 

 189J, pp. 170 186; UNNA, " Ueber die Reifung unserer 

 Farbsto/e," in Zeit. f. u-is*. Mik., viii, 4, 1892, p. 483). This 

 change is known as " ripening," and until it has taken place 

 the solutions are not fit to use for staining. 



Hitherto it has been the practice to rely (quite uncon- 

 sciously so far as the chemical theory is concerned) on the 

 spontaneous absorption by the solutions of oxygen from the 

 air to effect this " ripening/' but it has now been discovered 

 (by both MAYER and UNNA independently) that nothing is 

 easier than to bring about the reaction artificially all that 

 is necessary being, for instance, to add to a solution of haema- 

 toxylin containing alum a little neutralised solution of per- 

 oxide of hydrogen or other powerful oxidising agent. The 

 solution becomes almost instantaneously dark blue, " ripe," 

 and fit for staining, thus definitely confirming the truth of 

 the hypothesis. 



A solution of pure, uncombined haematein, however, would 

 not afford a selective stain such as we require in histology ; 

 it would be at most a feeble dye. The usual solutions (I am 

 not here speaking of Weigert's or Heidenhain's or similar 

 processes) all contain alum, and Mayer holds that the active 



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