ON STAINING WITH COAL-TAB COLOURS. 199 



stated as a very general rule that colours that do not give a nuclear stain by 

 tlie regressive method will wash out those that do. But RESEGOTTI'S expe- 

 riments do not seem to me to constitute a case in point. For he used the 

 second colour, if I understand him rightly, in alcoholic solution ; so that it 

 remains uncertain how far the differentiation should be attributed to the 

 second colour itself, and how far to the alcohol used as a vehicle. The same 

 remark applies to BENDA'S Safranin-and-Lichtgriin process. 



267. Clearing. The differentiation having been carried to 

 a satisfactory point, as described in 265, the extraction 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 iciJl 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, etc.; see the chapter on Clearing Agents). If you 

 have used neutral alcohol for washing out, you had perhaps 

 better clear with clove oil, as neutral 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. 



When the clearing is accomplished to your satisfaction, 

 either 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, etc.). Chloroform should be avoided, either as a clearer 

 or as the menstruum for the mounting medium. 



288. General Results. The results depend in great measure 

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

 them a prolonged fixation in Flemmmg's strong chromo- 



