INTRODUCTION

Anatomists at the College of Veterinary Medicine at North Carolina State University first came into contact with plastinated specimens in late 1983 and immediately decided to incorporate the technique into their teaching program. As has been the case with many other plastinators, the first Step was to attend the next, regularly scheduled International Conference on Plastination (San Antonio, 1984). It was soon evident that the greatest difficulty to overcome for any beginning plastinator is the building of the actual plastination unit.

Following the  Conference,  Dr  Harmon Bickley, of (at that time) The University of Texas Health Science Center at San Antonio, was called and asked a few questions about the unit being used there. Probably the most influencing bit of Information passed on by Dr Bickley was the comment that he would try to find an old freeze-dryer vacuum chamber if he was starting again to assemble such a unit. This was reasonable in that a freeze-dryer chamber is specifically built for vacuum. It is cylindrical (for greatest strength), well- sealed and fitted with a gasket and a heavy door.

It was then realized that the cooling System of a freeze-dryer could be used since it is specifically intended to maintain the temperatures needed for plastination. Also, a freeze-dryer comes equipped with a vacuum pump, capable of reaching the 5 microns of pressure desirable in plastination.

It gradually became apparent that there would be no need to disassemble a freeze- dryer to build a plastinator. All that was necessary to convert one to the other was to simply add a valve that could be used for vacuum control. A bonus not anticipated at the time was that, having done this, the freeze-drying capability of the machine would still be intact.

Having used a commercial freeze-dryer (Virtis Co. Model 220-PR) as a plastinator for the past three years, the author feels that scientists at this institution have an unusual opportunity to communicate Information that might be helpful to others who are either starting  plastination or considering a change of equipment. The purpose of this article is to discuss the Special features and advantages of the freeze-dryer plastination apparatus.

OBSERVATIONS

1. Commercially available freeze-dryers come equipped with vacuum pumps of sufficient strength and capacity for plastination and have refrigeration Systems intended to hold the temperatures.
2. The only modification needed to give a freeze-dryer plastinating capability is the addition of a valve to the vacuum line. (Our plastinator was "built" in 1/2 hour at a cost of $23.00).
3. Many individuals  planning  to  start plastination have access to freeze-dryers and need not purchase a new set of For example, plastination was begun without delay by the Animal Science Department of this  institution  because a freeze-dryer was available  and  not being  used.  State and university  property  storage agencies  often are  able  to  provide  surplus  freeze-dryers (sometimes without charge).     These may be as good as new or in need of minor repair. Even  vacuum  pumps  are  common surplus items.
4. Freeze-dryers (and plastinators) are commercially  available. These  units  are professionally    assembled  and  guaranteed. Such machines cost about the same as might be spent assembling  a more  makeshift apparatus and often have a larger vacuum chamber.  Acquiring a commercially available machine          often results in a  substantial savings of time and effort.  Table  1  is provided as a means of comparing cost and capacity.
5. Commercially available freeze-dryers are easily modified to a top-load position if desired or, alternatively, it is not expensive to fabricate an aluminum box to fill the available The box used at this institution cost $80.00 and has a volume of about 2 cubic feet. It, has proven quite serviceable.
6. Most commercially available plastination devices have vacuum chambers of 2-4 cubic feet.   Although fully capable of serving as a primary infiltration apparatus, such units also make ideal secondary, plastinators  that can be devoted exclusively to an advanced process such as sheet plastination.
7. Freeze-dryer-derived plastinators take up little floor space, a major concern in most The unit used by the vacuum chamber (in the form of a cylinder 18 inches in diameter and 24 inches deep). Another consideration is that they also are equipped with wheels and can be easily moved.
8. A converted freeze-dryer serves not only has an exceptional plastination unit (The one used by the author has operated continuously for 3 years without a single ) but also provides a second major function for no additional cost. The author has freeze-dried many anatomical specimens, as well as several rattlesnakes, turtles, birds and small mammals WHILE plastinating laboratory specimens.
9. A major advantage of the converted freeze-dryer; is that the ice sludge which tends to form on the surface of the impregnation polymer is no longer a problem. A freeze-dry unit removes and traps moisture. This is due to the only real difference between a freeze-dryer and a plastinator, the incorporation of a condensing chamber. This condenser usually operates at -55 to -60 degrees Centigrade and accumulates the sublimated water. Impregnation is usually begun with the condenser turned off and the freeze-dryer functioning as any other plastinator. If turned on early during impregnation, the condenser will accumulate acetone, unless pressure is reduced very slowly. After the first few days, the condenser is turned on and begins to scavenge water. Not only does this keep the silicone impregnation mixture cleaner it also permits impregnation with less perfect specimen dehydration.
10. Even the least expensive freeze-dryers have lighted vacuum chambers, making bubble monitoring very easy.  There is no need to open a freezer to view the impregnation since the heavy acrylic door is completely transparent. Due to the depressed solvent activity of acetone at this very low temperature, the door is not affected by its vapor. The unit used by the author shows no sign of solvent damage after 3 years of continuous use.