Wholemoiints in Jelly Media 



General Principles 



Glycerol jelly is the only type of water- 

 miscible medium known to most workers. 

 Many objects, both plant and animal, 

 which are usually prepared in glycerol 

 jelly, are much better mounted by the 

 method described in the last chapter, and 

 the author would most warmly recom- 

 mend to workers who have been using 

 glycerol jelly that they try one of the 

 methods there described. 



Formulas for the jelly media, the use of 

 which is described in the present chapter, 

 are given in section M 12.1 of Chapter 26, 

 and it will be seen that they are all essen- 

 tially the same. That is, they consist of a 

 dispersion of gelatin, which has been di- 

 luted with glycerol until the required index 

 of refraction is obtained, and they have 

 added to them some preservative. The 

 older glycerol jellies, designed for use in 

 European laboratories, do not in general 

 contain sufficient glycerol to withstand the 

 drying effects of an American laboratory. 

 The author has in his possession many 

 deep wholemouhts of fairly large crusta- 

 ceans which remained perfect for ten years 

 in England but which dried and cracked 

 after only two years in the United States. 

 There is little to choose among any of the 

 media, apart from the consideration just 

 given, and practice will soon permit the 

 mounter to select the one which works best 

 in his hands. 



Nature of the Process 



Mounts prepared in glycerol jelly may 

 be made either on flat slides or as deep 

 wholemounts. Glj'cerol jelly can be used 

 for larger objects than can the gum media 

 of the last chapter and, except for botan- 



ical specimens, the use of glycerol jelly is 

 largely confined to the preparation of 

 permanent slides of unstained crustaceans. 

 These media are sohd at room temperature 

 and must be melted before use. Material 

 cannot be mounted directly from water 

 unless the objects are soaked for a long 

 time in molten jelly to allow some of the 

 glycerol to penetrate. Mounts made from 

 specimens taken directly from water are 

 liable to have the jelly crack away from 

 the object as it cools. Moreover, these 

 media are not in their own right good 

 preservatives so that material placed di- 

 rectly from water into them is liable par- 

 tially to decompose before the mount 

 stabihzes. lit is conventional to transfer 

 objects to these media from 50% alcohol, 

 but it is better to harden the objects first 

 in alcohol than to transfer them from 

 alcohol to 50% glycerol and thence into 

 the molten medium. 



Process of Mounting 



There are three separate stages in the 

 preparation of glycerol-jelly mounts. The 

 first is hardening the object; the second is 

 getting the object from the hardening 

 fluid into the 50% glycerol; and the third 

 is the transfer from the 50% glycerol onto 

 the slide. 



As these mountants cannot be used for 

 stained specimens, there is little object in 

 using any fixative other than alcohol. The 

 transfer from the hardening alcohol to the 

 glycerol, however, must be by such stages 

 as will insure that the object does not col- 

 lapse through osmotic pressure. This 

 makes it impossible satisfactorily to 

 mount the majority of nematode worms in 



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