CLEARING. 63 



Eesegotti obtained the best results by washing out methyl 

 violet or dahlia with eosin or acid fuchsin (Saiirefuchsin). 



FLEMMING has obtained important results by first double- 

 staining sections with safranin followed by gentian violet, 

 and then treating them with concentrated aqueous solution 

 of orange, which, in virtue of its acid qualities, washes out 

 most of the gentian (see the details of the process in the 

 chapter on Combination Stains, 258). 



It has been made out by KUHNE (Centralbl. f. Bakteriol. u. Parasiterik., 

 xi, 1892, p. 756 ; Journ. Roy. Mic. Soc., 1892, p. 708) that saturated or 

 strong solutions of malachite green in anilin oil will wash out fuchsin, 

 methylen blue and crystal violet from sections (the process described by 

 Kiihne is one for the staining of bacteria in sections, and I cannot say how 

 far it is applicable to histological ends). 



The student will note that the colours in the second of Eesegotti'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, begamot 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 

 pouring the clearing agent over them. 



