190 CHAPTER XIII. 



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

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

 tiation ought to 4)e Controlled under the microscope. The 

 sections should t'o'^^s 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 than an hour, and mounted. 

 The results differ, in Heidenhain's view, according to the 

 duration of the treatment 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, blue 

 preparations will be obtained. These show a very intense 

 and highly differentiated stain of all nuclear structures, 

 cytoplasmic structures being pale. If t'he baths in the iron 

 .and in the stain have been prolonged (twelve to eighteen 

 "hours), and the subsequent differentiation in the second iron 

 bath also duly prolonged, Hack preparations will result. These 

 show chromosomes stained, " central corpuscles " stained in- 

 tensely black, cytoplasm sometimes colourless, sometimes grey, 

 in which case achromatic spindle-fibres and cell-plates are 

 stained, connective -tissue fibres black, red blood- corpuscles 

 black, micro-organisms sharply stained, striated muscle very 

 finely shown. 



Dr. MAYER, writing to me, doubts that the blue or black 

 tone is conditioned by the duration of the mordanting and 

 staining baths ; and my observations confirm this view. 



I most highly recommend this stain, which, like BENDA'S, 

 is one of the very finest I am acquainted with. It may be 

 used either with sublimate or alcohol material, or after liquid 

 of Flemming. The process is extremely easy to manage. 

 It is only applicable to sections, which should be thin, best 

 not more than 8 ju in thickness. The preparations are per- 

 fectly permanent. It has been said that this process frequently 

 gives rise to amorphous precipitates in the tissues. I find that 

 it does sometimes, but not to any very injurious extent. 



Later (Zeit. f. wiss. Mile., xiii, 1896, p. 186), Heidenhain gives further 

 instructions for the employment of this stain in the study of his " central 

 corpuscles." All alcohol should be removed from the tissues by means of 

 distilled water before bringing them into the mordant. This should be a 



