112 H^MATEIN AND OTHER ORGANIC STAINS. 



CHAPTER XI. 



H^MATEI'N (HJIMATOXYLIN) AND OTHER ORGANIC STAINS. 

 A. Hsematoxylin and Hsematein. 



174. Theory of Haematoxylin Staining. It appears to be now 

 thoroughly well established (see NIETZKI, Chemie der organ- 

 ischen Farbsto/e, Berlin, Springer, 1889, pp. 215217) that 

 the active colouring principle of hsematoxylin dyes is h&ma- 

 tein ; and further, that the haematein of the usual histological 

 staining solutions is a product of the oxidation of their con- 

 tained haematoxylin by means of the air to which they are 

 exposed (see MAYER, " Ueber das Farben mit Hamatoxylin" 

 in Mitth. a. d. Zool. Station zu Neapel, Bd. x, Heft 1, 1891, 

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

 in Zeit.f. wiss. Mik., viii, 4, 1892, p. 483). This change is 

 known as " ripening/' and until it has taken place the solu- 

 tions 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 haerna- 

 toxylin containing alum a little neutralised solution of per- 

 oxide of hydrogen. The solution becomes almost instan- 

 taneously dark blue, " ripe," and fit for staining, thus 

 definitively confirming the truth of the hypothesis. 



Mayer goes further. A solution of pure uncombined 

 haematein would not afford a. selective stain such as we 

 require in histology ; it would be at most a dye. The usual 

 solutions (I am not here speaking of Weigert's or similar 

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

 agent in them is a compound of haematein with alumina 



