200 CHAPTER XIV. 



aceto-osmic mixture, and have differentiated after staining 

 with acid alcohol and cleared with clove oil, you will get, 

 with some special exceptions,, nothing stained but nucleoli 

 and the chromatin of dividing nuclei, that of resting nuclei 

 remaining unstained. If you have given a lighter fixation, 

 with Flemming's weak mixture or some other fixing agent 

 not specially inimical to staining, and have differentiated 

 after staining with neutral alcohol, you will get the chromatin 

 of resting nuclei stained as well. 



269. HENNEGUY'S Permanganate Method (Journ. de I'Anat. et de la 

 Physiol., xxvii, 1891, p. 397). This method is based on the fact, discovered 

 by HENNEGUY, that permanganate of potassium is a mordant for many 

 anilin dyes, and will enable a good stain to be procured in cases in which 

 the usual methods fail. 



Sections are treated for five minutes with 1 per cent, solution of perman- 

 ganate of potassium. They are then washed with water and stained (for 

 about half the time that would have been taken if they had not been mor- 

 danted with the permanganate) in safranin, rubin, gentian violet, vesuvin, 

 or the like. The stain that succeeds the best is a safranin solution prepared 

 with anilin water and absolute alcohol (see below, 272). After staining 

 they are differentiated with alcohol, followed by clove oil in the usual way. 

 The progress of the decoloration should be controlled under the microscope, 

 in order that it may be stopped at the proper moment. It goes on in general 

 slowly, and the slower it proceeds the more selective will be the resultant 

 stain. The decoloration sometimes continues even after the sections have 

 been mounted in balsam, especially if all traces of clove oil have not been 

 removed before mounting. It may thus happen that preparations which are 

 insufficiently washed out at the moment of mounting show a perfectly 

 differentiated stain twenty-four or forty-eight hours afterwards. The stain 

 is either purely nuclear, or in part plasmatic, according to the extent of the 

 differentiation. I consider that it may occasionally be useful. 



The mordanting action of permanganate of potassium on anilin stains is 

 so energetic that if it have been overmuch prolonged before staining with 

 safranin, or, still more, with rubin, it becomes almost impossible to wash 

 out the sections properly ; it may be necessary to leave them for a month or 

 more in clove oil. 



270. OHLMACHER'S Formaldehyde Process (Medical News, February 

 16th, 1895). Ohlmacher states that formaldehyde is a powerful mordant 

 for tar colours. Tissues may either be mordanted separately by treatment 

 for a short time (one minute is enough for cover-glass preparations) with a 

 2 per cent, to 4 per cent, formalin solution; or the formalin may be com- 

 bined with the stain. One gramme of fuchsin dissolved in 10 c.c. of absolute 

 alcohol may be added to 100 c.c. of 4 per cent, formalin solution. Or satu- 

 rated alcoholic solution of gentian violet, or methyl violet 5 B, may be added 

 to 4 per cent, formalin solution in the proportion of 1 : 10. Or formalin- 



