STAINS AND STAINING 45 



should be warned that during the last twenty years of his life, Stras- 

 burger, who had been a leader in technique, cut very few sections and 

 did practically no staining, but used preparations made by assistants. 

 Let us now consider a few of the most important stains. 



THE HAEMATOXYLINS 



The most important haematoxyhns are Heidenhain's iron-alum 

 haematoxylin, Delafield's haematoxylin, Mayer's haem-alum, and 

 Boehmer's haematoxyhn. 



All the haematoxylins mentioned contain alum, and, according to 

 Mayer, who has written the most important work on haematoxylin 

 stains,^ "the active agent in them is a compound of haematin with 

 alumina. This salt is precipitated in the tissues, chiefly in the nuclei, 

 by organic and inorganic salts there present (e.g., by the phosphates), 

 and perhaps also by other organic bodies belonging to the tissues." 

 These salts are fixed in the tissues by the Idlhng and fixing agent, and 

 when the stain is applied a chemical comljination results. 



The first American haematoxylin was not satisfactory. It was dark 

 and did not stain well. Manufacturers bleached it, but that made the 

 staining worse. They then made a darker, but better, product. If crys- 

 tals are dark colored, feel sticky when rubbed between the fingers, and 

 go into solution quickly, the stain is not likely to be satisfactory. 

 Crystals of a light yellowish sand color, dissolving slowly and requiring 

 about six weeks to ripen, are much better. Haematoxyhns stain well 

 after any of the fixing agents described in the preceding chapter, but 

 they are most effective when used after members of the chromic-acid 

 series. 



Heidenhain's iron-alum haematoxylin. — This stain, introduced by 

 Heidcnhain in 1892, immediately gained great popularity and now, 

 after more than 40 years' constant use, still maintains first place in 

 cytological investigations. Two solutions are used, and they are never 

 mixed : 



A. Four per cent aqueous solution of ammonia sulphate of iron. 



B. One-half per cent aqueous solution of haematoxylin. 



In making solution A, use the violet ferric crystals, not the ferrous. 

 The first solution acts as a mordant, i.e., it does not stain, but pre- 



1 "Ueber das Farben mit Hamatoxylin," Miltheilungen aus der Zoologischen 

 Station zu Neapel, 10:170-186, 1891, and "Ueber Hamatoxylin, Carmin und ver- 

 wandte Materien," Zeitschriftfiir wissenschaftliche Mikroscopie, 16:196-220, 1899. 



