PRESERVATION OF SPECIMENS IN PLASTICS. 47 



ethyl alcohol (or 99-percent isopropanol) , and then rinsed in a second 

 clean bath of the same solvent mixture. In extreme cases, several such 

 immersions and rinsings may be required to remove all the extractable 

 matter that might otherwise have a detrimental effect upon the finished 

 mount. Carbon tetrachloride, chloroform, or dioxane may also be 

 used for this purpose if preferred. 



Soft or fleshy specimens that contain considerable amounts of mois- 

 ture should generally be washed in warm water and rinsed in 50-percent 

 alcohol. They should then be subjected promptly to the first step of 

 the appropriate preservation procedure. 



Specimens containing limited amounts of moisture, which are com- 

 posed of thin tissues and are capable of being air-dried without pre- 

 liminary preservation, usually require no cleaning other than the re- 

 moval of dust or other undesirable matter on the surface. This should 

 be done with a soft brush or feather, or with a gentle stream of air, as 

 in the case of dry specimen material. 



Preservation and Dehydration 



In preparing specimens for embedment in methacrylate resins, the 

 principal aim is to bring them into a stable moisture-free state with 

 minimum alteration of shape and color. Protection from actual contact 

 with the liquid resin is also necessary in certain instances in order to 

 prevent undesirable changes in the appearance of the specimen or in the 

 plastic block during embedment. 



Since various classes of specimen material require different procedures 

 for preservation, dehydration, and protective coating, the particular 

 treatment to be employed for a given specimen should be based on the 

 requirements of the class to which it belongs. In applying the general 

 directions given below for the various classes of material, it should be 

 borne in mind that experimentation will often be necessary in order to 

 determine the most effective procedure and, on the other hand, that 

 occasional specimens will be encountered for which no entirely suitable 

 preparatory treatment can be devised. 



Rigid specimen material with durable pigmentation. — Mature grains, 

 seeds, sections of wood, everlasting flowers and other sturdy, dry plant 

 material, and also such specimens of animal material as can be satisfac- 

 torily dried in the open air without change in appearance, including 

 bones, teeth, claws, shells, and insects with firm integuments, can 

 usually be prepared for embedment by dehydration alone. The neces- 

 sary dehydration can be carried out conveniently at room temperature 

 in a desiccator, preferably under vacuum, where it should be allowed 

 to remain for at least 24 hours. In the case of specimen material that 

 can withstand moderate heating without change in appearance, drying 

 for 3 or 4 hours in an oven at a temperature of around 70° C. (between 

 165° and 170° F.) may be employed as a more rapid means of dehydra- 

 tion. If the specimen is not to be used as soon as dehydration is com- 

 pleted, it should be kept in a dry condition until the embedding work 

 is started. 



Rigid specimen material with unstable pigmentation. — This class of 

 material includes such specimens as dry plant bulbs, roots, corms, 

 bark, woody fungi and lichens, as well as various objects of animal 

 origin. Because of the rigidity of this material, its dehydration may be 



