Publisher Summary The method of dehydrating a material by a process of vacuum desiccation at a low temperature is of great scientific and industrial importance. The biochemist and pharmacist use the method on a large scale in the preparation of proteins, hormones, and other labile products. The bacteriologist uses the method extensively in the preservation of cultures. The cytological use of the method is among the earliest applications and has developed independently of the other and later uses. The procedure of cytological freezing and drying is conveniently divided into three stages: the initial sampling and cooling of the tissue, the vacuum desiccation, and the preparation of the dried tissue for microscopical examination. Quenching involves taking a sample of tissue and immersing it in a cold bath. By this means, all chemical reactions and diffusion of substances in the tissue are slowed down to a minimum. The structure of the specimen immediately after efficient quenching is that of a vitrified or a microcrystalline solid. The changes that tend to take place are devitrification, recrystallization to relieve the mechanical stresses of the sudden contraction in quenching, and crystal growth.