CLEARING. 59 



Mik., v. 3, 1888, p. 320, that it may be stated as a very general rule that 

 colours that do not give a nuclear stain by the indirect method will wash out 

 those that do. Thus he found that 



Safranin, Dahlia, Methyl Violet, Gentian Violet, Kubin, Victoria Blue, 

 Magenta, Basic Fuchsin, are washed out by the following : 



Congo, Methyl Green, Iodine Green, Nigrosin, Methylen Blue, Orange, 

 Ponceau, Acid Fuchsin, Aurantia, Cyanin, Eosin, Methylic Eosin, Magdala 

 Red, Bordeaux, Vesuvin. 



Resegotti obtained the best results by washing out methyl violet or 

 dahlia with eosin or acid fuchsin (Saiirefuchsin). 



The student will note that the colours in the second of Resegotti's lists 

 may be turned to account for washing out and producing a contrast stain at 

 the same time ; he should also take note that this washing out is a true 

 chemical decoloration, and if pushed too far will invade the nuclei as well 

 as the rest of the tissues. 



99. Clearing, The washing out of the colour may be stopped 

 by putting the sections into water ; but the general practice 

 is to clear and mount them at once. 



You may clear with clove oil, which will extract some more 

 colour from the tissues. Or you may clear with an agent that 

 does not attack the stain (cedar oil, bergamot oil, xylol, toluol, 

 naphtha, &c. See the chapter on Clearing Agents). If you 

 have used pure alcohol for washing out, you had perhaps 

 better clear with clove oil, as pure alcohol does not always, 

 if the staining have been very prolonged, extract the 

 colour perfectly from extra-nuclear parts. But if you have 

 not stained very long, and if you have used acidulated 

 alcohol for washing out, clove oil is not necessary, and it may 

 be better not to use it, as it somewhat impairs the brilliancy 

 of the stain. A special property of clove oil is that it helps 

 to differentiate karyokinetic figures, as it decolours resting 

 nuclei more rapidly than those in division. 



Some colours are much more sensible to the action of clove- 

 oil than others; and much depends on the quality of this 

 much adulterated essence. New clove oil extracts the colour 

 more quickly than old. 



Series of sections on slides are conveniently cleared by pour- 

 ing the clearing agent over them. 



When the clearing is accomplished to your satisfaction, 

 mount in damar or balsam, or stop the extraction of the colour 

 if clove oil have been used by putting the sections into some 

 medium that does not affect the stain (xylol, cedar oil, &c.). 



