CHAPTER XIII. 

 H^IMATEIN (H^IMATOXYLIN) STAINS. 



232. Theory of Hsematoxylin Staining. It appears to be now 

 thoroughly well established (see NIETZKI, Chemie der organ- 

 ischen Fdrbstoffe, Berlin, Springer, 1889, pp. 215 217, and 

 MAYKE, Mittli. Zool. 8 tat. Neapel, x, 1891, p. 170) that the 

 active colouring principle of the usual histological staining 

 solutions is heematein, a product of the oxidation of their 

 contained hsematoxylin by means of the air to which they 

 are exposed (see MAYBE, " Uebei- das Farben mit Hamatosey- 

 lin," in Mitt.lt. a. d. Zool. Station zu Neapel, Bd. x, Heft 1, 

 1891, pp. 170 186 ; UNNA, " Ueber die Reifung unserer 

 Farbsto/e," in Zeit. f. wisn. M-ik., 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 heematem, 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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