762 . HISTOLOGIC TECHNIG 



MOUNTING 



After staining, the sections are opaque; they must be rendered 

 transparent for microscopic examination. This is accomplished by per- 

 meating the sections with oil; but since oil and water are not miscible, 

 the tissue must first be thoroughly dehydrated with alcohol. Immers- 

 ing 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 clari- 

 fying 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 cretici, cajuput, clove, carbol-xylol 

 (pure carbolic acid, melted, 25 to 33 c.c.; xylol, 75 to 67 c.c.), and xylol. 

 Xylol (xylene) is the most desirable in that it is perfectly 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. Carbol-xylol has the advantage of a slight affinity for water; 

 this is also true of the heavier oils. Complete dehydration is therefore 

 not required. Bergamot is desirable for celloidin sections, but has the 

 disadvantage 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 

 carbol-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 section, 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 pre- 



