Freehand Sections 83 



minutes after the purple color appears. If the cellulose walls show 

 only a faint purplish color, put the sections back into the stain and 

 try a longer period. If the color is a deep purple or nearly black, 

 add a little hydrochloric acid (one drop to 50 c.c. is enough) to 

 the water. It is better to put the drop into a bottle of water and 

 shake thoroughly before letting the acidified water act upon the 

 sections. As soon as the sections begin to appear reddish, which may 

 be within 4 or 5 seconds, pour off the acidified water and wash in 

 drinking-water, changing the water three or four times a minute, until 

 the reddish color caused by the acid has been replaced by the rich 

 purple color so characteristic of haematoxylin. The acid not only 

 secures differentiation by dissolving out the stain from lignified 

 structures more rapidly than from cellulose walls, but it also removes 

 the disfiguring precipitates which almost invariably accompany 

 staining with Delafield's haematoxylin. The acid also washes out 

 the safranin; it is for this reason that the washing after safranin 

 should be stopped while there is still some red color in the cellulose 

 walls. The acid should not only reduce the density of the haema- 

 toxylin and remove precipitates, but should also remove the little 

 safranin which may remain in the cellulose walls. After the purple 

 color has appeared, the sections should be left in water for 20 or 30 

 minutes. They might be left for several hours. 



Xow place the sections in 50 per cent alcohol for 1 minute, then 

 in 95 per cent alcohol for 1 minute, 100 per cent alcohol for 5 minutes, 

 and then transfer to xylol. As soon as the sections become clear- 

 in about 1 to 5 minutes they are ready for mounting in balsam. If 

 the sections do not clear readily, as may be the case if the air is 

 damp, or if the alcohol or xylol is not quite pure, transfer from the 

 absolute alcohol to clove oil, which will clear, even if the absolute 

 alcohol is rather poor. Then transfer from clove oil to xylol; the 

 objection to mounting directly from clove oil is that preparations 

 harden more slowly than when mounted from xylol. With a section- 

 lifter, or scalpel, or brush, transfer three or four sections to a clean, 

 dry slide, put on one or two drops of balsam, and add a cover, first 

 heating it gently to remove moisture. If xylol has been used for 

 clearing, it is necessary to work rapidly; for the sections must never 



