Wholemounts in Resinous Media 



General Principles 



Mounting whole objects by the methods 

 described in the last five chapters involves 

 little preparation of the specimen but a 

 great deal of preparation of the mount. In 

 preparing wholemounts in resinous media 

 a great deal of attention must be paid to 

 the preparation of material, although the 

 actual mounting is simple. 



Resinous media are used for whole- 

 mounts not only because they permit 

 mounting stained objects but more par- 

 ticularly because they impart to the speci- 

 men a great degree of transparency. This 

 transparency comes from the increase in 

 the index of refraction when the specimen 

 is completely impregnated with the resin. 

 These resins are not, however, miscible 

 with water, hence the water must first be 

 removed {dehydration) and then the de- 

 hydrant replaced with some material 

 {clearing agent) with which the resin itself 

 is miscible. Before these operations the 

 specimen must be killed and hardened 

 {fixed) and it is customary to stain the 

 specimen in order to bring out those in- 

 ternal structures which would become in- 

 visible, were they not colored, through the 

 increase in transparency. All of the follow- 

 ing operations must, therefore, be con- 

 ducted and will be discussed in turn : 



1. narcotizing and fixing 



2. staining 



3. dehydrating 



4. clearing 



5. mounting 



Narcotizing and Fixing Specimens 



Hard objects such as small arthropods, 

 hairs, and the hke may be dehydrated and 



mounted directly into resinous media,' but 

 are far better prepared according to the 

 manner described in Chapter 4. Most ob- 

 jects which are mounted in resinous media 

 are, however, too^soft to withstand the 

 process of dehydration and^clearing with- 

 out special treatment. Though hardening 

 and fixing agents were once considered as 

 separate, they are now usually combined 

 into a solution known as a fixative. Before 

 deahng with fixatives, however, it is neces- 

 sary to point out that few small animals, 

 on being plunged into a fixative, will re- 

 tain their shape, so that it is necessary 

 first to narcotize them in some solution 

 which will render them incapable of 

 muscular contraction. 



Narcotization may be caused either 

 through the blocking of nerve impulses 

 which cause contraction, or by some treat- 

 ment which will inhibit the actual con- 

 traction of the muscle. For blocking nerve 

 impulses there are a wide range of nar- 

 cotics available (see Chapter 19, AF 50) 

 and making a choice between them must 

 be a matter of experience. It is to be rec- 

 ommended, in the absence of experience, 

 that one of the solutions containing co- 

 caine be first tried, since cocaine is the 

 nearest approach to a universal narcotic 

 known to the author. Should cocaine not 

 be available, crystals of menthol may be 

 sprinkled on the surface of the water con- 

 taining the specimen. It is very important 

 to distinguish between narcotization and 

 kilUng, for a good wholemount cannot be 

 made from a specimen which has been 

 permitted to die in the narcotic. 



Narcotization should always proceed 

 slowly; that is, one should add a small 



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