HJCMATEIN (HJSMATOXYLIN) STAINS. 179 



nffords a means of preventing the " over-ripening " brought 

 about by excessive oxidation. 



If, however, it be still preferred to use hsematoxylin, this 

 should not be done by dissolving the haematoxylin crystals 

 straight away in the other ingredients of the solution. The 

 solutions should be made up from a strong stock solution 

 made by dissolving haematoxylin crystals in absolute alcohol : 

 one in ten is a good proportion. This solution should be 

 kept for a long time months, at least, a year if possible ; 

 it gradually becomes brown, and should not be used till it 

 has become quite dark. It has then become to a great extent 

 oxidised into haematein, and the staining solutions made up 

 from it will be at once fairly ripe. 



233. UNNA'S Half-ripe Constant Stock Solution (Zeit.f. wiss. Mik., 

 viii, 4, 1892, p. 483). A ripe solution may be made constant (see last ) 

 by simply adding a reducing agent to it. Various reducing agents are 

 available for tbis purpose (see tbe original paper) ; the most convenient 

 method is the simple addition of a little sulphur. The following formula is 

 recommended : 



Hsematoxylin . .1 



Alum 10 



Alcohol 100 



Water 200 



Sublimed sulphur 2 



If the sulphur be added to the hsBmatoxylin solution only when the latter 

 has become somewhat strongly blue, i- e. after two or three days' time, the 

 stage of oxidation attained by the solution will be fixed by the sulphur. 

 The solution in this state may be used for staining. MAYER (Mitth. Zool. 

 Stat. Neapel, xii, 2, 1896, p. 309) finds that the sulphur process does not 

 preserve the solutions for long, whilst for some unexplained reason the 

 simple addition of glycerin does ; see below, " GLYCH.EMALUM." 



234. Concerning Haematein. The following is taken from the 

 two papers of MAYER quoted above, 205, 232. Haematein 

 is entirely, though with difficulty, soluble in distilled water 

 and in alcohol, giving a yellowish-brown solution, which 

 remains clear on addition of acetic acid. Alkalies dissolve 

 it with a blue-violet tint. 



It is now found in commerce ; but MAYER has hitherto only 

 been able to procure it in a perfectly pure state from GEIGY 

 & Co., in Bale. But there is also found in commerce an 

 ammonia-compound of haematein Hsematein-Ammoniak, also 

 known in commerce as Hsemateinum crystallisatum ; this may 



