246 J. W. GROVES ON SECTIONS OF ANIMAL TISSUES. 



The mixture may be kept in a bottle, but no more cement should be 

 made {i.e., should be mixed with gold size) than required for imme- 

 diate use, as it sets quickly and becomes unworkable. 



Certain precautions are necessary to be observed in varnishing 

 fluid or glycerine preparations ; they are — 



1. Use no more glycerine or fluid than is just necessary to fill 

 up the space beneath the cover. 



2. If the medium should escape beyond the cover glass, soak it 

 up with a piece of blotting paper, being careful not to press the 

 cover, or the cement will run in afterwards. 



3. Wash the slide round the cover and the edge of the cover 

 glass also if necessary with a sable pencil, then run a ring of cement 

 on the slide just beyond the edge of the cover, a second round the 

 edge of the cover, and a third bridging over the space between the two. 



4. Three or four coats should thus be put on, taking care on each 

 occasion that the previous coat is dry. 



Of preservative mounting media, the most useful are balsam, 

 glycerine, and glycerine jelly. 



Canada balsam should be exposed to heat until it becomes quite 

 brittle, allowed to cool, then it should be dissolved in benzole till as 

 thin as glycerine, and should always be used cold. 



Glycerine. — Specimens which have been hardened in chromic 

 acid or bichromates may be mounted in pure glycerine alone, but if 

 they have been hardened in spirit, glycerine and carbolic acid (in 

 the proportion of glycerine 15 parts to carbolic acid 1 part) is 

 better, as it is less refractive and prevents the sections becoming 

 granular. 



For carmine stained preparations it is well to add a trace of 

 acetic acid to the glycerine (ttlij : ^i). 



Glycerine jelly is a good medium, as it offers the advantages of 

 glycerine without the chance of leaking, but it is rather difficult to 

 prepare, and therefore had better be bought. 



A jelly composed of 



Glycerine ") t , 

 Gelatine j«l ual P arts 



is very useful ; the glycerine should be warmed, and the gelatine 

 (Nelson's) be allowed to dissolve in it. 



Acetate of potash in a saturated solution is used for some 

 preparations, but is liable to leak. The same may be said of 

 Goadby's fluid. 



