1 70 ('II. AFTER XIV. 



that does not effect the stain (xylol, cedar oil, etc.). Chloro- 

 form should be avoided, either as a clearer or as the men- 

 struum for the mounting medium. 



283. General Results. The results depend in great measure 

 on the previous treatment of the tissues. If you have given 

 them a prolonged fixation in Fleniming's strong chromo-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, find have differentiated after 

 staining with neutral alcohol, you will get the chromatin of 

 resting nuclei stained as well. Either process may also stain 

 mucin, the ground-substance of connective tissues (especially 

 cartilage), the bodies of Nissl in nerve-cells, and the yolk of 

 ova. 



284. HENNEGUY'S Permanganate Method (Journ. de VAnat. et de la 

 PhysioL, xxvii, 1891, p. 397). Sections are treated for five minutes with 

 1 per cent, solution of permanganate of potassium. They are then 

 washed with water and stained (for about half the time that would have 

 ]>een taken if they had not been mordanted with the permanganate) in 

 safranin, rnbin, gentian violet, vesuvin, or the like, and are differentiated 

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



The mordanting action of the permanganate is so energetic that if it 

 has been overmuch prolonged before staining with safranin, or, still 

 more, with rnbin, it becomes almost impossible to differentiate the 

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

 more in clove oil. 



285. OHLMACHER'S Formaldehyde Process (Medical News, Feb- 

 ruary 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 l)e combined with the stain. One gramme of fuchsin or 

 methylen blue dissolved in 10 c.c. of absolute alcohol may be added to 

 100 c.c. of 4 per cent, formalin solution. Sections are said to stain in 

 half a minute and to resist alcohol much more than is the case with 

 those treated by the usual solutions. 



286. Safranin. One of the most important of these stains, 

 on account of its power, brilliancy, and permanence in balsam, 



