CHAPTER 9 



Mounts and Mountants 



The final mounting of an object or section for microscopic examina- 

 tion consists in cementing it between a slide and coverslip in a medium or 

 "mountant" that will preserve it permanently and retain it in a suffi- 

 ciently transparent condition for study. There are two kinds of mountants: 

 ( 1 ) those which are miscible with water and to which objects may be 

 transferred directly and ( 2 ) those which are not miscible with water and 

 which require that the object be prepared by dehydration and clearing as 

 described in the last chapter. 



Too little attention is paid nowadays to the water-soluble mountants, 

 which are really much more suitable for mounting many objects than is 

 the balsam usually employed. Stained objects, of course, cannot be 

 mounted in these aqueous media, but a large number of small inverte- 

 brates, particularly arthropods, make better preparations in gum media 

 than they do in balsam. 



GUM MEDIA 



There are two types of gum media: (1) those of relatively low index 

 of refraction, which do not render the objects placed in them very trans- 

 parent and (2) those of a very high index of refraction for use in circum- 

 stances where a transparency almost equivalent to a balsam mount is re- 

 quired. The two most useful of the low index of refraction media are: 



Farrants's Medium: 



Water 40 ml 



Gum acacia 40 g 



Glycerin 20 ml 



Phenol 0.1 g 



The original formula used a saturated solution of arsenous oxide as a 

 preservative, but phenol is just as good for preventing the growth of 

 fungi. This medium is rather difficult to make up, for it is difficult to 



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