52 MISC. PUBLICATION 679, U. S. DEPT. OF AGRICULTURE 



rigidity, after dehydration has been carried out in a liquid medium, by 

 immersing them for several days in xylene (xylol) or toluene (toluol). 

 In transferring specimens from absolute alcohol to xylene, and also 

 from xylene to methacrylate monomer, three or more stages should 

 be employed to insure proper elimination of the preceding liquid. It is 

 also advisable not to permit soft or fragile specimens to dry out by 

 evaporation during transfer, because they are liable to shrink or become 

 distorted. 



Caterpillars and other soft-bodied insect larvae, as well as certain 

 worms and various other zoological specimens that have nonrigid in- 

 teguments, can in some cases be prepared in an acceptable manner by 

 killing them in water heated to approximately 60° C. (140° F.) and then 

 gradually bringing the temperature to the boiling point and holding it 

 there for 10 minutes, or longer if necessary, to coagulate the proteins 

 and produce the desired toughening of the tissues. It is general^ neces- 

 sary to dehydrate specimens thus prepared by transferring them in the 

 usual manner through several concentrations of alcohol, beginning with 

 70-percent and ending with 100-percent (absolute) . These dehydrated 

 specimens should finally be hardened by several daj^s' immersion in 

 xylene as previously explained. 



Caterpillars and similar specimens can also be prepared, if preferred, 

 by inflating and hardening them after removal of the body contents 

 (15, 16). The method for doing this consists in laying the caterpillar 

 on a sheet of paper and forcing out the contents hy gently rolling a pencil 

 or glass rod lengthwise along it, starting just back of the head. A glass 

 tube drawn to a fine tip is then inserted in the anus, and the caterpillar 

 is inflated to its natural size by carefully blowing into it. The distended 

 specimen, with the tube still inserted, is finally hardened and dried by 

 heating it cautiously over a low flame or in a moderately hot oven. 

 Specimens prepared in this manner should preferably be stored in a 

 desiccator to keep them dry until ready for impregnation and embed- 

 ment. 



Preparation of certain types of specimens that are difficult to process 

 by any of the preceding methods may also be undertaken, if facilities 

 permit, by means of the freeze-drying procedure outlined for processing 

 unstable nonrigid specimen material in the next section (p. 54). How- 

 ever extensive equipment and special training are required for carrying- 

 out this procedure satisfactorily. 



The second type of nonrigid durably pigmented specimen material 

 is represented by flowers, leaves, and other plant parts that consist 

 largely of thin tissues and contain comparatively small amounts of 

 moisture. Generally specimens of this type having moderately stable 

 pigmentation require no preliminary preservation and can be prepared 

 for embedment simply by dehydration, followed if necessary by appli- 

 cation of protective coatings. It should be borne in mind, however, 

 that in this group many specimens may be encountered with which 

 acceptable results cannot be obtained with any of the preparatory 

 methods thus far employed. Such specimens must be considered un- 

 suitable for embedment in methacrylate resins unless special procedures 

 can be devised for them. Because of this uncertainty, it is always 

 advisable in the case of flowers and similar material to try out prepara- 

 tion and embedment procedures experimentally with test material 

 before attempting to work on the actual specimens. 



