NO. 3549 FREEZE-DRY PRESERVATION — SHOWER 23 



temperature of less than —25° C. Rapid freezing also creates smaller 

 ice crystals, causing less tissue distortion during the process. 



Techniques for faster drying. — The greatest amount of water 

 is removed early in the drying cycle when a specimen's dried shell is 

 thinnest and offers the least impedence to the escape of water vapor. 

 The rate of weight loss due to the escape of vapor approaches zero 

 with the completion of drying. If a specimen chamber is loaded with 

 a great number of fresh specimens, the water-vapor atmosphere 

 will be very great during the first few days, possibly exceedmg the 

 capacity of the system. If, however, specimens are introduced at 

 spaced intervals, the same number of specimens can probably be 

 processed without exceeding the system's vapor-removing capacity, 

 and a constant level of water-vapor removal may be approached. 



By drilling holes in the back or bottom portions of specimens, their 

 drying surfaces are increased and the area of their epidermal layers 

 is decreased, allowing water vapor to escape more rapidly. Skinning 

 one side of a specimen serves a similar function in that it removes 

 epidermal tissue that would otherwise act as a vapor barrier. 



Evisceration of a specimen also reduces its water content consid- 

 erably; however, the removal of water-laden organs requires incision, 

 removal of the viscera, filling the body cavity mth cotton or similar 

 material, all of which requires time and involves some of the less 

 desirable features of taxidermy. 



A record should be maintained of each specimen's weight since 

 observmg the weight reduction (by removing the specimen from the 

 chamber and weighing it) is the best method for deternunmg when a 

 specimen is completely dry. A specimen should be left in the chamber 

 for one or two days after the loss of weight ceases to be apparent. 

 This is especially true for rodents such as mice or rats with a scaly 

 epidermis on their tails. The tails dry slowly and it is therefore 

 advisable to perforate their undersides and keep the specimens in 

 the chamber beyond their apparent drying times. 



Conclusion 



As technology advances, it becomes apparent that freeze-dry 

 will be an ever-growing field. Plans are already underway for 

 increasing the Smithsonian facilities. Theoretically, there is no 

 limitation to the ultimate size or numbers of specimens that at one 

 time could be processed in this manner. It is hoped that this paper 

 will help to encourage the growth and exchange of further ideas on 

 the freeze-drying process. 



