-1-0 MISC. PUBLICATION (579, U. S. DEPT. OF AGRICULTURE 



that tend to discolor the plastic or inhibit its polymerization, and they 

 must not be subject to changes in appearance due to contact with a 

 surrounding; medium having an index of refraction different from that 

 of air. 



The types of plant material generally suitable for embedment in 

 methyl or ethyl methacrylate resins include mature grains and seeds, j 

 dried fruits, nuts, cones, stems, roots, and sections of wood and bark. 

 A limited number of durable flowers, including strawflowers and other 

 everlastings, and certain types of tough or rigid leaves lend themselves 

 to preservation by this method; but flowers and leaves in general usually 

 prove to be too fragile or too readily affected by the resin to yield satis- 

 factory results. 



The zoological specimens that lend themselves to preservation by this 

 method include both adult and immature forms of most of the inverte- 

 brates, and also many of the smaller mammals. Insects with rigid 

 integuments give particularly good results, as do also such objects as 

 bones, teeth, horns, claws, carapaces, and shells. Soft-bodied adult 

 insects, as well as larvae and eggs may also be embedded satisfactorily 

 if they can be completely infiltrated with plastic and are strong enough 

 to withstand distortion or rupture during polymerization. Sections of 

 organs and body tissue have been embedded successfully after dehydra- 

 tion by freeze-drying or other special preparation. Hair, fur, and 

 feathers give only moderately satisfactory results, and butterflies, 

 moths, and other objects that owe their coloration mainly to diffraction 

 rather than to pigmentation are generally unsuitable for embedment in 

 plastics of the methacrylate type. 



PREPARING SPECIMENS FOR EMBEDMENT 



Before the preservation of biological specimens by this method is 

 undertaken their suitability for embedment in methacrylate plastics 

 should be ascertained by reference to the classes of material reported 

 to be satisfactory, which are described under "Selection of Specimens", 

 and, if any doubt exists, by making preliminary trial embedments. 

 It is also advisable to determine as definitely as possible the preparation 

 requirements of the specimen material by reviewing the following pro- 

 cedures, and, if necessary, by carrying out such experimental tests as 

 may seem to be in order for preliminary preservation and dehydration. 



Cleaning Specimen Material 



Material that is to be embedded should be carefully cleaned to remove 

 all dirt and other undesirable substances. If the specimens are in a drj- 

 condition, it is usually advisable to dust them off with a brush or feather, 

 or with a gentle stream of air, and then to wash them by immersion for a 

 few minutes in 95 percent alcohol or dry acetone. After being washed, 

 they must be allowed to stand in the open air until the solvent has 

 evaporated; then they should be stored in a desiccator for a day or more 

 to make sure that all free moisture has been removed. Specimens 

 containing oils or other extractable substances that tend to discolor or 

 modify the plastic during embedment, should, after they are thoroughly 

 dry, be immersed for 24 hours in a solvent mixture composed preferably 

 of 40 parts of toluene, 30 parts of acetone, and 30 parts of absolute 



