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



be a convenient way of directing its flow and building up proper support 

 around the specimens. A cardboard box or other suitably porous con- 

 tainer should be used in order to let the moisture escape readily, and it is 

 advisable to perforate the bottom or hinge the sides so that the packing 

 medium can be disposed of readily, after dehydration has been completed, 

 without damaging the dried specimens buried in it. 



In carrying out this dehydration procedure, the perforated box should 

 just be set in a slightly larger one that has entire sides and bottom and 

 that serves to prevent undue escape of sand from the inner box. After 

 pouring approximately 1 inch of dry clean sand or other suitable granular 

 or pulverized material into the box, place the specimens in position upon 

 it. Then apply additional sand carefully, preferably through a funnel, 

 in such a manner as to cover the specimens completely without dis- 

 turbing the position of any of their parts. The specimens should be 

 buried at least an inch below the surface, and if they have a tendency 

 to curl or twist during drying, or if light-weight packing material is 

 employed, it is advisable to pour on an additional 1 or 2 inches. 



Specimens packed in sand or other nonabsorbent medium should be 

 kept in the open air at a temperature about 10° C. (18° F.) above room 

 temperature for 2 or 3 days. When silica gel or other activated absorbent 

 is used, it is best to enclose the box in an airtight case containing a small 

 amount of anhydrous calcium sulfate or calcium chloride to aid in 

 absorbing the moisture. 



At the end of the drying period the box containing the specimens should 

 be raised from its outer container and the sand or other packing medium 

 allowed to drain out. The dried specimens should then be carefully taken 

 out, preferably with forceps or tweezers, and dust or particles of packing 

 medium clinging to the surface should be removed with a soft brush or 

 a feather, or in some cases with a gentle jet of air. If no compressed air 

 source is available, blowing through a glass .tube or straw will give satis- 

 factory results if not continued long enough for moisture in the breath to 

 dampen the specimen unduly. In the case of very fragile or brittle mate- 

 rial, however, it is usually advisable to let it absorb a slight amount of 

 moisture from the breath or from the air in the room in order to reduce 

 its brittleness before attempting to clean away the adherent particles. 

 After being cleaned, the dehydrated specimens must be kept dry by 

 storing them in a desiccator or other suitable airtight container until 

 they are to be coated or impregnated. 



In the case of specimens that cannot be prepared satisfactorily by 

 packing in a granular moisture-permeable or moisture-absorbing medium, 

 good results sometimes can be obtained, if suitable equipment is avail- 

 able, by the freeze-drying procedure substantially as outlined for non- 

 rigid unstable specimens in the next section. 



Nonrigid material with unstable pigmentation. — This class of spec i- 

 men material includes body tissue together with various types of zoolog- 

 ical and botanical specimens that require special preparation to retain 

 both shape and color. Considerable experimentation is sometimes re- 

 quired for determining which of the known procedures is best, or for 

 working out special procedures, for preparing such material; and. further- 

 more, numerous specimens may be encountered that prove to be altogether 

 unsuitable for embedment in methacrylate resins. 



For the preparation of body tissue and organs, as well as certain 



