EXAMINATION AND PRESERVATION MEDIA. 



Anat., xix, 1881, p. 322; Sci. Gossip, 1882, p. 257; Journ. 

 Roy. Hie. Soc. [N. S.], iii, 1883, p. 145; Morphol. Jahrb., vi, 

 1880, p. 469 ; Journ. Roy. Mic. Soc. [N. S.], ii, 1882, p. 583). 



See further details concerning these and other solutions in 

 former editions. 



I quite acknowledge the special beauty of definition 

 obtained by means of damar solutions, but I am convinced 

 that not one of these solutions can be depended on for really 

 permanent preservations. Sooner or later, sometimes after a 

 few weeks or days, or it may be only after months or years 

 the granules mentioned in 438 will make their appearance. 



443. Colophonium. A solution of colophonium in turpen- 

 tine was first recommended by KLEINENBEEG. I find it to be 

 most highly recommendable. 



This medium sets very slowly, so that ample time is afforded 

 for arranging objects in it. Both KLEINENBERG and MAYER 

 warn against the employment of absolute alcohol as a solvent ; 

 the preparations are beautiful at first, but soon become 

 spoiled by the precipitation of crystals or of an amorphous 

 substance. 



The turpentine solution keeps perfectly limpidj gives very 

 good definition, and is altogether so excellent a medium that 

 I am surprised that it is not more used. It should be recom- 

 mended to beginners. And, as stated in 438, I consider 

 that for many purposes it is perhaps the best and most reliable 

 medium known. To make the solution, I add small lumps of 

 colophonium to a quantity of rectified oil of turpentine kept 

 in a stove, and when a sufficiently thick solution has been 

 obtained, filter twice, the filtering being done in the stove. 

 About a fortnight is required for the whole process. The 

 solution should not be too thick, as it thickens somewhat 

 with age. The palest sorts of colophonium should of course 

 be selected. 



Of course the slowness of drying of this medium is a great 

 objection to its use in cases in which it is required to study 

 the preparations with oil-immersion lenses as soon as possible 

 after mounting. In the winter a slide will take about a 

 month before it will be hard enough to be safe with oil- 

 immersion lenses ; whereas an alcohol-balsam mount will be 

 dry enough in a couple of days. 



