only to methylene blue in the number of different purposes for which 

 it is used. It is valuable not only because it is a powerful nuclear 

 stain and a chromatin stain par excellence, but also because it has 

 striking polychrome properties. With the proper differentiation it 

 is possible to get several shades intermediate between blue and red 

 to show in the same preparation. 



Haematoxvlin is seldom used alone, as it has little affinitv for the 

 tissues in itself, even after "ripening" when it is largely converted 

 into haematein. Some form of mordanting is ordinarily required; 

 and most of the haematoxylin formulae either call for some metallic 

 salt or specify previous treatment of the sections with one. In 

 plant histology, however, there is some use for haematoxylin alone. 

 Its greater affinity for plant than for animal tissue implies the 

 presence of aluminium, copper, or iron in the former. In fact 

 haematoxylin can be used as a very delicate reagent for iron or 

 copper. 



Perhaps the best known formulae for staining with haematoxy- 

 lin are the combinations with aluminium, generally in the form of 

 alum. Bohmer's alum haematoxylin (1865), altho no longer used, 

 is of much historic interest as it was the first stain of this type to be 

 used. The best known at present is Delafield's alum haematoxy- 

 lin, which is very useful tissue stain with great affinity for chroma- 

 tin and nuclei, and has much value in staining cellulose walls in 

 vascular plants. Another alum haematoxylin used for similar 

 purposes is that of Ehrlich. 



Mayer's haemalum is another well known alum combination. 

 In this stain haematein is first prepared and then combined with 

 alum. The name haemalum, proposed by Mayer, is now generally 

 accepted for this combination, and various other haemalum form- 

 ulae have since been proposed. They are useful chromatin stains 

 and are called for in various special procedures. 



Mayer has also combined haematein with aluminium chloride, 

 his haemacalcium calling for this salt and calcium chloride, while 

 his muc-haematin contains aluminium chloride and glycerin. The 

 latter is used for staining mucin. 



The iron combinations are perhaps equally valuable. The 

 original iron haematoxylin was that of Benda; but the best known 

 at present is M. Heidenhain's, which is one of the most useful 

 histological and cytological stains, both in botany and zoology. It 

 is a powerful stain for chromosomes and centrosomes, and is of use 

 for bringing out the middle lamellae in wood. Various other 

 modifications of iron haematoxvlin have been used, but thev are 

 all similar in principle. Ordinarily the iron salt is not mixed with 

 the stain, but is used for a preliminary mordanting of the tissue. 



Haematoxylin has been combined with chromium, one of the 

 early staining methods being that of R. Heidenhain, which called 

 for potassium bichromate as a mordant. Various recent modifi- 

 cations are in use today, such as that of Apathy, for staining general 



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