WASHING OUT. 61 



advantage. For researches on nuclei the solutions made with 

 anilin had better be employed only with preparations well 

 fixed in chromo-aceto-osmic acid, as the basic anilin oil may 

 easily attack chromatin if not specially well fixed. 



97. Washing out. Washing out is generally done with 

 alcohol, sometimes pure, sometimes acidulated (with HC1). 

 The stained sections, if loose (celloidin sections), are brought 

 into a watch- glassful of alcohol; if mounted in series on a 

 slide they are brought into a tube of alcohol (washing out 

 can be done by simply pouring alcohol on to the slide, but it 

 is better to use a tube or other bath). It is in either case 

 well to just rinse the sections in water before bringing them 

 into alcohol. 



The sections in the watch-glass are seen to give up their 

 colour to the alcohol in clouds, which are at first very rapidly 

 formed, afterwards more slowly. The sections on the slide 

 are seen, if the slide be gently lifted above the surface of the 

 alcohol, to be giving off their colour in the shape of rivers 

 running down the glass. In a short time the formation of 

 the clouds or of the rivers is seen to be on the point of ceasing ; 

 the sections have become pale and somewhat transparent, and 

 (in the case of chrom-osmium objects) have changed colour, 

 owing to the coming into view of the general ground colour 

 of the tissues, from which the stain has now been removed. 

 (Thus chrom-osmium-safranin sections turn from an opaque 

 red to a delicate purple.) At this point the washing out is 

 complete, and must be stopped instantly. 



It is generally directed that absolute alcohol be taken for 

 washing out. This may be well in some cases, but in general 

 strong (95 per cent.) spirit is found to answer perfectly well. 



The hydrochloric acid alcohol process had better only be 

 employed with tissues well fixed with " Flemming," as with 

 tissues imperfectly fixed it may cause swellings. Further, 

 the acid extracts the colour much more quickly from resting 

 nuclei than from kinetic nuclei, which is an advantage or a 

 disadvantage according to the end in view. 



As a rough and ready guide to the beginner, it may be 

 stated that washing out should be done with pure alcohol 

 whenever it is desired to have resting nuclei stained as well 

 as dividing nuclei ; the other processes serving chiefly to 

 differentiate mitoses. 



