Fluid Wholemoiints in Nonaqueous Media 



General Principles 



Nature of the Process 



The mounting of whole objects in non- 

 aqueous media is essentially the same 

 process as mounting objects in aqueous 

 media: that is, the objects are enclosed in 

 the preservative medium in a very flat 

 box, the floor of which is formed by the 

 slide, the top of which is formed by the 

 coverslip and the sides of which are 

 formed either of cement, or by a cell. 

 There are not, however, so many possible 

 choices among cells and seahng media as is 

 the case with aqueous mounts, for the 

 choice of the medium itself dictates every 

 subsequent step. 



Choice of the Medium 



Only three nonaqueous media are 

 commonly used in mounting: these are 

 glycerol, bromonaphthalene, and Uquid 

 petrolatum. These should never be used 

 when any aqueous substitute is available, 

 nor should a fluid medium be used if a 

 mountant which will harden under the 

 coverslip (see the next three chapters) 

 can be employed in its place. Each of these 

 three media will be discussed in their 

 turn. 



Glycerol is widely used as a mountant 

 in those cases in which a water-miscible, 

 high-refractive-index material is required 

 and in which a medium of the type dis- 

 cussed in the next chapters cannot be em- 

 ployed. The principal reason that such 

 media cannot be used is the difficulty of 

 transferring delicate objects to, say, 

 glycerol jelly without causing a collapse 

 of their walls, while it is comparatively 

 simple to get delicate objects into glycerol 

 by evaporation. This technique is usually 



applied to nematode worms, and some- 

 times to small arthropods or very delicate 

 coelenterates, which should be fixed in 

 the ordinary manner and then transferred 

 very gradually to alcohol and from alcohol 

 to ^ % glycerol in alcohol. The alcohol is 

 then slowly evaporated, leaving the 

 material in pure glycerol. It is almost 

 impossible to seal a deep cell full of 

 glycerol, and mounting in this material 

 should be confined to cells built out of 

 cement or to shdes in which a concave 

 hollow has been ground. 



Sealing Glycerol Mounts with Dichro- 

 mate Gelatin 



There are three ways in which a 

 glycerol-filled cell may satisfactorily be 

 sealed. The first is with the aid of molten 

 gelatin, appUed from a turntable in the 

 manner described in the last two chapters, 

 and then varnished with any good cement; 

 the second method involves the apphca- 

 tion of a molten resinous medium; the 

 third method uses petrolatum. In the case 

 of the first method it is better to use a 

 solution of gelatin containing potassium 

 dichromate, which becomes insoluble on 

 exposure to hght, than to use straight 

 gelatin; and it is doubtful if the formula 

 of Riiyter 1934 or 1935 (Chapter 28) can 

 be improved. 



A narrow ring of material is turned on 

 the sUde, in the manner previously de- 

 scribed, the ring being made slightly 

 smaller in diameter than the size of the 

 coverslip to be used and just sufficiently 

 thick to keep the covershp from bearing 

 on the object. This cement shrinks on 

 drying so that a ring must be turned 



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