PRESERVATION OF SPECIMENS IN PLASTICS 21 



cause discoloration during the interval required for the preservative to 

 diffuse into their tissues. The time required for this curing under 

 refrigeration is usually 10 to 20 days for thin permeable material and 

 may extend to 3 or 4 weeks or even longer for very succulent specimens 

 or those with highly impervious epidermal tissue. 



Among the indications that a specimen has become completely cured 

 are: (1) The development of a wrinkled puckery appearance that may 

 be accompanied by considerable shrinkage; (2) increased flexibility 

 except in woody or hard fibrous parts; and (3) noticeable toughening and 

 increased resistance to bruising. If there is any doubt as to whether a 

 specimen has been fully cured, it is advisable to extend the curing time, 

 because specimens removed prematurely from preserving fluid tend to 

 develop discoloration before they can be dehydrated. There is little 

 danger of overcuring the material because it will usually remain un- 

 changed when it is left in the preserving fluid for a number of months, 

 provided it is kept properly refrigerated. 



Laying out and working over cured specimens after removal from 

 preserving fluid bath. — When thoroughly cured in the preserving bath, 

 the specimen should be removed with wooden or plastic tongs or forceps 

 and most of the viscous fluid on it permitted to drain off. It is then 

 placed on a mounting sheet, preferably 0.030 inch thick, which is backed 

 with plain paper laid upon a sheet of waxed paper large enough to 

 provide a 2-inch margin all around. 



The cured material should be laid out in as natural a position as 

 possible with a wooden splint or similar implement . All folds or creases 

 in leaves and flowers, and all twists or tangles must be straightened out 

 at this time, because these conditions cannot be remedied later. The 

 cover film should now be placed over it in such a way as to keep the 

 specimen in position. This is best accomplished by working with the 

 splint under the film and with the fingers on its outer surface while it is 

 being lowered into position. The waxed paper should next be folded 

 over its edges so as to form a marginal pocket about 1 inch wide all 

 around to receive the excess preserving fluid as it is extruded. 



In working over the layout, the air bubbles should be eliminated by 

 pressing out the excess fluid in a manner that will flood the specimen 

 and displace all the free air in and around it. This is done by light 

 finger pressure on the cover film. The excess fluid should then be 

 worked away from the specimen into the surrounding area, and finally 

 extruded into the marginal pockets formed by the folded waxed paper. 

 A plastic squeegee or roller, operated through an interposed work sheet 

 of rigid type cellulose acetate film 0.002 inches thick will be found 

 helpful in pushing the fluid out of the area around the specimen. Pres- 

 sure should not be applied to the specimen itself with such an instru- 

 ment. The waxed paper marginal pockets should then be trimmed off 

 and discarded, and after the back of the mounting sheet has been 

 cleaned and wiped dry the layout should be placed in a drying box or 

 cabinet for dehydration. 



DEHYDRATION AND PREPARATION FOR MOUNTING 



After the preserved specimen has been laid out as described (p. 14), 

 it must be dehydrated to remove all free moisture from it and also from 

 the preserving fluid that still remains around it. This may be done 



