HAMATE IN 151 



of " ripening." or of preparing h.Tmatein separately, are given 

 further on, and constitute a great progress (§§ 315, 316, etc.). 

 P^'or 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 

 ascertaining whether the solution at any moment contains 

 sufficient ha^matein to afford a good stain. And here a second 

 difficulty arises : the oxidising process continuing, the solutions 

 become " over-ripe " ; the hasmatein, through further oxidation, 

 passes over into colourless compounds, and the solutions begin to 

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

 stantly varying proportions of " unripe," " ripe," and " over- 

 ripe " 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 ha^matoxylin, 

 but hccmatein, should be taken in the first instance for making the 

 staining solution. 



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 ahvays preferable to start from hsematoxylin. 

 In this case, it should not be done by dissolving the hsematoxylin 

 straight away in the other ingredients of the staining 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 of a vinous red, and should not be used till it has become 

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

 hfematein, and the staining solutions made up from it will be at 

 once fairly ripe. 



Hfematein (or hsematoxylin) affords a stronger stain than 

 carmine, and gives better results with tissues fixed in osmic or 

 chromic mixtures. The alum solutions are indicated for staining 

 in bulk, iron ha?matoxyIin for sections. 



278. Haematoxylin is found in commerce in the form of crystals, 

 either colourless or brownish, easily soluble in either water, 

 glycerin or alcohol. The brownish crystals are to be ]:)referred 

 since the unbleached dye keeps better in solutions. In America, 

 only the certified dye should be bought. Should difficulty be 

 experienced in getting good selectivity with the American product, 

 McClung {Science, 58, 1923, p. 515) recommends adding 3 drops 

 of a saturated solution of lead acetate to 100 c.c. of a i per cent, 

 solution of haematoxylin and then shaking. After standing some 

 hours, a black precipitate is formed. After filtration, a bright 

 clear liquid remains which should stain satisfactorily. 



