Illinois Natural History Survey - University of Illinois

How Scientific Specimens are Prepared

Several different methods are used to preserve specimens, depending on the type of organism and how the specimen will be used.

Drying. Used with mammal and bird skins, bones, mollusk shells, insects, and plants. Shells require little preparation. Skins are often stuffed after the flesh is removed. Bones must be thoroughly cleaned, a process that is often facilitated by putting the carcass in a colony of flesh-eating beetles. Insects are usually pinned or mounted on tiny paper "points." Plants are usually pressed flat, dried, and then glued on special highly durable paper.

Pickling. Used with amphibians and reptiles, fish, crustaceans, soft-bodied parts of mollusks, delicate insects, and other invertebrates. Grain alcohol (ethanol) is the standard preservative. The specimens are stored in appropriate-sized containers, including small vials, bottles, and even large steel tanks.

Slide mounting. Small insects and other invertebrates are often mounted directly on microscope slides, which allows them to be examined microscopically without handling. The genitalia of many larger insects are essential for identification and may also be mounted on a slide accompanying the insect. Slide mounting is also frequently used for fungi.

Freezing. Microsporidia, microscopic organisms that often infect insects, are best preserved by freezing at very low temperatures (-321deg.F) in liquid nitrogen, where they live in a state of "suspended animation" (see the article in this issue on the microsporidia collection). Many seeds can be stored, alive, the same way. Freezing can also be used to preserve both animal and plant tissue collections for DNA and other chemical analyses.

Living cultures. Collections of bacteria and many fungi are best maintained as living cultures. Obviously this requires intense labor, and few institutions are able to make the long-term commitment to maintaining living collections.

Geoffrey A. Levin, Center for Biodiversity



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