TORPOR. - It is a phenomenon characteristic of certain mammals (rodents, insectivores, chiropterans, carnivores, etc.), represented by the reduction, down to a minimum, of physiological organic activities (respiratory, circulatory activity, etc.), so much so that the animal appears to be in a state of deep sleep; torpidity, although associated with sleep, is a distinct phenomenon from II. Other animals, such as, among heterothermic vertebrates, amphibians, reptiles, and some fish (e.g., lungfish), exhibit similar phenomena that are better indicated by the terms estivation or hibernation. Estivation is also exhibited by invertebrates (e.g., earthworms, snails, some crustaceans), and hibernation by many insects.
With torpidity, estivation, and hibernation, animals overcome unfavorable environmental conditions in summer and winter, especially those related to temperature, and in summer also to the lack of water; they are therefore annual cyclical phenomena. Among birds, there are no examples of torpidity because they overcome these conditions through migration.
With torpidity, metabolic and assimilative activity is suspended; the respiratory ratio between CO2 emitted and O2 absorbed is reduced to one-third; the body temperature (in heterothermic animals) decreases significantly. At the end of torpidity, body weight is significantly reduced.
Torpidity, hibernation, and estivation are phenomena that can be associated with that of latent life, but in this field there are far more remarkable phenomena with the conditions of encystment and the life of spores and plant seeds.
Encystment, characteristic of many invertebrates (rotifers, tardigrades, worms, etc.), is marked by a very considerable dehydration and the formation of envelopes that may be derived from the animal's own integument; even the internal anatomical condition is profoundly modified. Under favorable conditions, the animal resumes water, and, with the reconstitution of its organs, returns to active life. Latent life was studied by Spallanzani, who called it «vita minima». Spores and seeds are also in a state of dehydration and, if conditions are not favorable, can maintain the «vita minima» for a very long time.
Phenomena of hypnosis and catalepsy should not be confused with torpidity; these represent pathological conditions or are induced by hypnotic maneuvers on neurotic or hysterical individuals (v. LETHARGY).