Desiccation is the process of drying by the employment of heat, dry air, or chemical agents which have an affinity for water. Examples of the class of desiccants or drying substances are fused chloride of calcium, quicklime, fused carbonate of potash, and oil of vitriol. The latter is employed by being placed in a separate vessel near the substance to be dried, and under a bell jar.
Not a few of the lower animals are said to be able to endure drying up without losing the power of recovery. Some of the Protozoa form protective sheaths or cysts from which they emerge on the return of moisture. Nematodes or thread-worms (paste-eels) have been known to revive after fourteen years' desiccation, but trials beyond this limit were unsuccessful. With those animals the interesting fact has been noticed that the longer the period of desiccation, the longer the time required for recovery. Rotifers are also described as reviving after prolonged and thorough desiccation, but experiments have shown that, in the case in question at least, only the associated eggs retained their life. The eggs rapidly developed on the return of moisture, but the adult organisms proved to be really dead. The bear-animalcules or Tardigrades have been thoroughly desiccated and even heated to a high temperature without, it is said, losing power of revivification. A state of latent life is also assumed in consequence of cold, absence of stimulus, &c., and a relative quiescence occurs naturally in hibernation, or pathologically in trance. Among the lower plants, resting spores, &c., may survive desiccation; and, among the higher, seeds are well known to have a similar power. See HIBERNATION, INSECTS, LATENT LIFE, MUD-FISHES, ROTATORIA, SLEEP, &c. For the desiccation of land-areas, see DESERT, ASIA.