THEOEY OF H^IMATOXYLIN STAINING. 113 



(" Hasmatein-Thonerde " Haematein-alumina) . He holds that 

 this salt is precipitated in the tissues (chiefly in the nuclei) by 

 certain organic and inorganic salts there present (for instance, 

 phosphates) ; perhaps also by other organic bodies belonging 

 to the tissues. Such salts are known to exist in living 

 tissues. By the process of " fixing" they are fixed there, 

 either in the same chemical state, as when such an agent as 

 alcohol is used for fixing ; or as fresh compounds formed by 

 the action of the fixing agent itself, as when such a fixing 

 medium as sublimate is used. 



The chief factor in the composition of these stains is, 

 therefore after the colouring substance itself, alumina, to 

 which, however, may be added some other bodies, such as 

 lime, which may play a secondary role (as, for instance, chlo- 

 ride of calcium does in Kleinenberg's solution) . 



It follows that the first difficulty with which the worker 

 with haematoxylin stains has to contend is that of getting his 

 haematoxylin duly oxidised into haematein, in order to the 

 formation of the desired haematein- alumina compound, or 

 lake. If this be done by the hitherto customary process of 

 leaving the solutions to " ripen " by the action of the air, 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 "over-ripe" constituents (the first and last being 

 useless for staining purposes), and, in consequence, their 

 staining power is very inconstant. 



These difficulties are only very imperfectly got over by 

 any of the very various methods that have been proposed 

 until lately. Now, however, thanks to the important dis- 

 coveries of MAYEE and UNNA, a great step in advance has 

 been taken. 



The great point in Mayer's work is that not haematoxylin, 

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

 the staining solutions. This at once relieves us from the 

 tedious and uncertain process of "-ripening'' in the old way. 

 We have a ripe solution to begin with. A discovery of 

 Unna's, to be mentioned below, affords a means of preventing 

 the " over-ripening " brought about by excessive oxidation. 



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