146 HMMATEIN (HMMATOXYLIN} STAINS. 



oxidising agent.* The solution becomes almost instantaneously 

 dark blue, " ripe " and fit for staining. Other methods of " ripen- 

 ing," or of preparing hsematein 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 ascertaining whether the solution at any moment 

 contains sufficient hsematein to afford a good stain. And here a 

 second difficulty arises : the oxidising process continuing, the 

 solutions become " over-ripe " ; the hsematein, 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 " over- 

 ripe " constituents (the first and last being useless for staining 

 purposes), and, in consequence, their staining power is very in- 

 constant. 



Logically, therefore, as concluded by MAYER, not hsematoxylin, 

 but hcematein, 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. 80 

 that it is always 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 

 hsematoxylin crystals in absolute alcohol : one in ten is a good 

 proportion. This solution should be kept for a long time months, 

 at leapt, 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 hsematein, and the staining 

 solutions made up from it will be at once fairly ripe. 



Hsematein (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 hsematoxylin for sections. 



238. Haernatoxylin is found in commerce in the form of crystals, 

 either colourless or browned by oxidation, easily soluble in either 

 water, glycerin, or alcohol. 



* Ee-in vented lately (Zeit. wiss. Mik., xxix, 1912, p. 69) by PIAZZA, 

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

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



