MOUNTING 669 



not miscible, the tissue must first be thoroughly dehydrated with 

 alcohol. Immersing thin sections in 95 per cent, alcohol for three 

 to five minutes is usually sufficient for this purpose unless xylol is 

 to be used as the clarifying oil or unless the stain is injured by so 

 prolonged an immersion. In either of these cases absolute alcohol 

 is to be used for dehydration, because of its more rapid and 

 thorough action. 



Clarification. Sections, either free or fastened to the slide, are 

 immersed in oil until clear. Free sections will at first float on the 

 oil, but when fully permeated will sink. Attached sections should 

 lose all traces of " milky " appearance. The following oils are 

 commonly used for clarification : Bergamot, origanum, cajuput, 

 clove, carbo-xylol (pure carbolic acid, melted, 25 to 33 cc., xylol, 75 

 to 67 cc.), and xylol. Xylol is the most desirable in that it is per- 

 fectly miscible with the balsam in which the section is usually 

 mounted, and is finally lost by evaporation. It will not act in the 

 presence of the least trace of water. Carbo-xylol has the advantage 

 of a slight affinity for water ; this is also true of the heavier oils. 

 Bergamot is desirable for celloidin sections, but has the disadvan- 

 tage of rapid deterioration, after which it dissolves the celloidin. 

 Either origanum or cajuput oil, or a mixture of the two, serves 

 well for celloidin sections, but leaves them somewhat stiffer than 

 does bergamot oil. The latter is therefore preferable for elastic 

 tissues. On the whole, origanum serves best for routine work with 

 celloidin sections, xylol or carbo-xylol for paraffin. 



After clarification celloidin sections must be transferred to a 

 slide. This is accomplished by means of a metal lifter or by a 

 strip of rice paper (ordinary cigarette paper does nicely). The sec- 

 tion, lying on the paper, is inverted upon the surface of the slide, 

 to which it remains adherent after the paper is gently lifted. The 

 excess of oil is then removed with blotting paper or by gentle 

 pressure with a folded towel, a drop of xylol-balsam applied, and the 

 cover glass dropped into position. The preparation is permanent. 



Xylol-balsam is prepared by adding to Canada balsam sufficient 

 xylol so that the mixture will have a thick, syrupy consistence, but 

 will drop from a glass rod without stringing. 



Sections may also be permanently mounted in glycerin without 

 previous dehydration, the edge of the cover glass being, after some 

 hours, covered with a ring of King's cement. 



Neutral Balsam. Sections may frequently be rendered more 

 permanent by the use of neutral balsam, prepared as follows : 



