H^MATBIN (HiEMATOXYLIN) STAINS. 157 



tiation, it should be taken extremely diluted (of a very fole 

 straw-colour, about 1 : 30 of water), and the progress of 

 the differentiation watched ; as if it be only diluted about 

 tenfold, for instance, the decoloration is extremely rapid. 

 See also last §. 



I also find that Benda's mordant is unnecessarily, some- 

 times harmfully, strong, and that the Liquor ferri may be 

 diluted tenfold with advantage. The duration of the bath 

 in the mordant is also for most purposes excessive as 

 directed by Benda. I find that thi'ee to six hours in the 

 solution diluted tenfold is generally sufficient, with favour- 

 able material. 



242. Heidenhain's Iron Haematoxylin (M. Heidenhain, 

 " tJber Kern und Protoplasma," in Festschr. fiir KoUiker, 

 1892, p. 118). — Sections are treated from half an hour to at 

 most two or three hours with a 1'5 to 4 per cent, solution of 

 ferric alum (ammonio-ferric sulphate). By this is always 

 meant in histology the double salt of ammonium and sesqui- 

 oxide of iron (NH^)2Fe3 (SO^)^, in clear violet crystals ; the 

 double salt of the protoxide, or salt of Mode in green 

 crystals, will not serve. If the crystals have become yellow 

 and opaque, they have gone bad, and should be rejected. 

 They ought to be kept in a stoppered bottle, and the solution 

 should be made in the cold (^Arch. niik. Anal.,, xliii, 1894, 

 pp. 431, 435). The sections are then washed with water 

 and stained for half an hour in an aqueous solution (of 

 about 0'5 per cent.) of haematoxylin. They are then rinsed 

 with water, and again treated with the iron solution, which 

 slowly washes out the stain. The progress of the differen- 

 tiation ought to be controlled under the microscope. The 

 sections should to this end be removed from time to time 

 from the alum solution, and put into tap-water whilst they 

 are being examined. This is favourable to the stain. As 

 soon as a satisfactory differentiation has been obtained, the 

 preparations are washed for at least a quarter of an hour in 

 running water, but not more tlian an hour, and mounted. 

 The results differ according to the duration of the treat- 

 ment with the iron and the stain. If the baths have been 

 of short duration, viz. not more than half an hour in the 

 iron and as much in the stain, hlue preparations will be 



