HJEMATEIN (KEMATOXYLIN) STAINS. 153 



easier than to bring about this change artificially ; all that is 

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

 toxylin containing alum a little neutralised solution of peroxide 

 of hydrogen or other powerful oxidising agent.* The 

 solution becomes almost instantaneously dark blue, " ripe ; 

 and fit for staining. Other methods of " ripening," or of 

 preparing haematein separately, are given further on, and 

 constitute a great progress. For under the old practice of 

 leaving staining solutions to " ripen ; by the action of the 

 air, it is necessary to wait for a long time before the reaction 

 is obtained. During all this time, it may be weeks or 

 months, there is no means, except repeated trial, of ascertain- 

 ing whether the solution at any moment contains sufficient 

 haematein to afford a good stain. And here a second difficulty 

 arises: the oxidising process continuing, the solutions become 

 " over-ripe "; the haematein, through further oxidation, passes 

 over into colourless compounds, and the solutions begin to 

 precipitate. They are therefore, in reality, a mixture in 

 constantly varying proportions of " unripe," " ripe," and 

 "overripe" constituents (the first and last being useless for 

 staining purposes), and, in consequence, their staining power 

 is very inconstant. 



Logically, therefore, as concluded by MAYER, not liema- 

 toxylin, but hsetnatein, should be taken in the first instance 

 for making the staining solution. This at once relieves us 

 from the tedious and uncertain process of "ripening' in the 

 old way. We have thus a ripe solution to begin with. 



But this is not always indicated ; for such solutions may 

 easily over-oxidise, either in the bottle or on contact with 

 the tissues. So that it is sometimes preferable to start 

 from hsematoxylin. In this case, it should not be done 

 by dissolving the haBmatoxylin straight away in the other 

 ingredients of the staining solution. The solutions should 

 be made up from a strong stock solution made by dissolving 

 hasmatoxylin 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 of a vinous red, and should not be used till it has 



* -Re-invented lately (Zeit. wiss. Mil:., xxix, 1912, p. 69) 'by PIAZZA, 

 who adds to Boehiner's solution about 20 per cent., to Delafield's about 

 7 per cent., to Ehrlich's about 12 per cent, of peroxide of hydrogen. 



