HIBERNATION. 887 



when, as is usual, these are cooler than the body. It also furnishes 

 the heat necessary to vaporize the water of the cutaneous and pulmo- 

 nary exhalations; it warms the air expired from the lungs; it heats 

 the secretions as well as the body itself; and, lastly, it warms the food 

 and drink taken into the body, when these are cooler than the inter- 

 nal organs, and aids in the solution of digestible substances, and in 

 their metamorphosis for the purposes of absorption. Of 100 parts of 

 heat given off by the body, 72.9 are lost by radiation from the sur- 

 face, 14.5 by evaporation from the skin, 7.2 by evaporation from the 

 lungs, 3.5 from warming the air used in respiration, and 1.8 by the 

 urine and solid excreta. 



As the standard of temperature remains constant within 2 or 3, 

 between hot and cold seasons, and Tropical and Arctic climates, the 

 quantity produced in the body depends on the external temperature, 

 and must be greater in cold climates, in which the loss is greater, than 

 in warm climates. The amount required to be produced is also modi- 

 fied by the degree of protection of the body, either by shelter or 

 clothing. 



Hibernation. 



Amongst the most remarkable phenomena presented by animal life, in the 

 temperate and cold regions of the earth, are those which are known under the 

 name of hibernation. During the winter season, a few Mammalia retire into 

 burrows or other shelter, and there, either under the influence of the low tem- 

 perature, or guided by an inherent instinct or an acquired feeling, pass into a 

 condition of torpor much more profound than ordinary sleep. The marmot, 

 dormouse, and hedgehog, are the most familiar examples of this hibernation 

 in the Mammalia. It is remarkable that no Birds are known to hibernate, 

 the belief once prevalent that swallows retired to the bottom of ponds to hi- 

 bernate, being erroneous. Amongst Reptiles, both serpents and snakes, as 

 well as land-tortoises, hibernate ; and in the Amphibia, the frogs and newts. 

 Both serpents and frogs have been kept in this condition, by artificial cold, 

 for three years. Hibernation in Fishes is not known, unless it be compul- 

 sory from freezing of the water. Of the Non-vertebrate animals, only terres- 

 trial species are known properly to hibernate, such as the land-snails and 

 slugs amongst the Mollusca, and the chrysalides of certain Insects, which pass 

 through a winter, before they change into the imago state. Even in the Pro- 

 tozoa, examples are met with, of a winter state or condition, in which those 

 animals undergo the process known as encystation, so called because in it, they 

 surround themselves with a protective cyst, in which they remain dormant, 

 until the return of warmth induces peculiar changes in them, for the repro- 

 duction of new animals. 



The condition of partial hibernation manifested by certain animals, which 

 collect a store of winter food, such as the beaver and others, is named spurious 

 hibernation. In this state, the circulation and respiration are not so dimin- 

 ished in activity, nor the temperature so reduced, as in true hibernation ; for 

 though the animals sleep much, they, from time to time, arouse themselves to 

 take food. 



In the true hibernating Warm-blooded animal, not only the nervous and 

 muscular systems are quiescent, but digestion entirely ceases, no food being 

 taken. The circulation is very slow ; the respiratory movements are almost, 

 or according to some, completely arrested ; the interchange of oxygen and 

 carbonic acid in the air-passages, can take place by diffusion only ; the ab- 

 sorption of oxygen and the evolution of carbonic acid, are very slight, and the 

 animal heat accordingly sinks ; so that, without protection from the cold of 

 the winter season, the animal would die. The respiration which continues is 

 supported by a store of fat, which serves as fuel during the dormant state ; 



