Natural Dyes 221 



Hematoxylin is without question one of the most important 

 biological stains. It is as valuable to the cytologist and histologist 

 as methylene blue is to the bacteriologist; and probably is second 

 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 be- 

 cause 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. 



Hematoxylin is seldom used alone, as it has little affinity for the 

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

 into hematein. Some form of mordanting is ordinarily required; 

 and most of the hematoxylin 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 hematoxylin alone. 

 Its greater affinity for plant than for animal tissue implies the 

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

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

 copper. 



Perhaps the best known formulae for staining with hematoxy- 

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

 alum. Bohmer's alum hematoxylin (1865), although no longer 

 employed, is of historic interest as it was the first stain of this type 

 to be used. The best known at present is Delafield's alum hema- 

 toxylin (see.Prudden, 1885), which is a very useful tissue stain 

 with great affinity for chromatin and nuclei, and has much value in 

 staining cellulose walls in vascular plants. Another alum hema- 

 toxylin used for similar purposes is that of Ehrlich (see Krause, 

 1926-7, p. 972). 



Mayer's hemalum (1891, 1899) is another well-known alum 

 combination. In this stain hematein is first prepared and then 

 combined with alum. The name hemalum, proposed by Mayer, is 

 now generally accepted for this combination, and various other 

 hemalum formulae have since been proposed. They are useful 

 chromatin stains and are called for in various special procedures. 



Mayer (1891, 1899) also combined hematein with aluminium 

 chloride, his hemacalcium calling for this salt and calcium chloride, 

 while his muci-hematein contains aluminium chloride and glycerin. 

 The latter is used for staining mucin. 



The iron combinations are perhaps equally valuable. The 

 original iron hematoxylin was that of Benda (1886); but the best 

 known at present is M. Heidenhain's (1892, 1896), which is one of 

 the most useful histological and cytological stains, both in botany 

 and zoology. It is a powerful stain for chromosomes and centro- 

 somes, and is of use for bringing out the middle lamellae in wood.* 

 Various other modifications of iron hematoxylin have been used, 

 but they are all similar in principle. Ordinarily the iron salt is 



