HIBERNATION 



mmsrrs 



703 



ami the ordinary daily sleep of a few hours in 

 which every animal indulges. There w also 

 \ degree of torpidity exhibited. The hedge- 

 hog and the dormouse may l>e rolled over and over 

 like a lull, without waking, and the black bear of 

 America is extremely dillicult. to arouse out of its 

 \\intei -sleep. Mn tin- othrr hand, the brown lear 

 of Silieria hilHsrnates lightly, ami is very dangerous 

 when awakened. The hedgehog, if disturbed, taken 

 a 'deep sonorous inspiration, followed by a few 

 feeble respirations, and then by total quiescence.' 

 This diHers from the stirring and then coiling itself 

 up .-iLiain which is the animal's way when awakened 

 out of an ordinary sleep. But, though sensation 

 and volition are dormant, the refle\ and excito- 

 inotory actions are keen, the slightest touch 

 applied to the spines of a hedgehog or to the 

 wings of a bat inducing one or two inspiratory 

 movements. But the hibernating badger is not 

 dillicult to reawake, and in its torpor, like all 

 hibernating animals, is not rigid. (5) Continuous 

 hihernators do not lay in stores of food. Inter- 

 mittent winter-sleepers generally do, while some 

 animals which are not true hibernators, but remain 

 only drowsy during the winter, retire to their 

 burrows to pass the days of famine above ground 

 in the midst of their abundant nuts and other 

 provender. All of these food-storers are vegetable- 

 eaters. The arctic fox is indeed the only excep- 

 tion to this 'rule, for though it is not any more 

 than the beaver a hibernator, it hoards up dead 

 lemmings, ermines, geese, hares, &c. against the 

 evil days of winter. An exception to intermittent 

 hibernators being thus provident is afforded by the 

 porcupine (Hystrix cristata) and the alpine mar- 

 mot. 



In its most pronounced forms hibernation differs 

 physiologically in several important steps from 

 ordinary sleep, though it is undoubtedly linked 

 with this function by a regular chain of links. 

 Cold we know produces drowsiness, which ends 

 in a fatal torpor, and on warm days a sleep steals 

 over the eyes which might, in kind if not in de- 

 gree, be compared with the aestival torpor of some 

 animals. In other respects, hibernation is more 

 akin to trance. Yet what is most puzzling about 

 it is that it affects only some animals which differ 

 little in habit from others which keep awake all 

 winter, and in the same region find food in abund- 

 ance. The polar bear sleeps while seals are plenti- 

 ful on the ice-floes, and the Noctule bat retires 

 while the cockchafers, in which it delights, are 

 numerous. Still, as it enables animals to live 

 within their area which might otherwise require 

 to migrate, we cannot refuse to admit that hiber- 

 nation plays an important part in the struggle for 

 existence, the survival of the fittest, and the means 

 whereby animals are confined within certain zoo- 

 geographical regions. But how it originated, or 

 whether it is a survival, like migration, from a 

 former condition of things, are problems which in 

 the present state of our knowledge cannot be 

 satisfactorily solved. 



Hibernatore, when they retire for the winter, 

 are unusually fat : when they emerge from their 

 hibernaculum they are unwontedly lean. They all 

 try to keep warm, the heat of their body being 

 nearly that of their hibernaculum. Yet if exposed 

 to greater cold they revive, and, if the temperature 

 is still further lowered, like other animals they 

 freeze to death. Ileviviscence is probably due to 

 the calls of nature, the observations of Horvath on 

 a zizel (Spennophilus citillus) showing that the 

 heat of the circumambient air does not rise while 

 the animal is awaking, though the temperature 

 of its body does. During dormancy the animal 

 functions are all but suspended. Excretions in 

 the bat are reduced to almost nothing, and the 



bean close the lower end of their alimentary canal 

 by a rcMinoiiH plug, known in Sweden a* ' tappen.' 

 Respiration and circulation are reduced to a mini- 

 mum. The air of a dosed jar containing a hiler 

 nating dormouse in unaltered. Other* can Hn\i\e 

 long in an atmosphere deprived of oxygen. A 

 I'.-it in a lethargic condition 1m* remained M 

 minutes under the water; ami thou/h thiee or 

 four minutes' immersion will, under other circum- 

 stances, Hufliee to drown a hedgehog, in a stale of 

 winter torpidity it can lnar twenty two and a half 

 with impunity (Mai-shall Hall). Carbon dioxide 

 has so little effect on a torpid marmot that one 

 lived after being four hours in this poi-onon- 

 Simon and Friedleben noticed that in some bluer 

 nators the thymus gland gets laden with fat just 

 before they retire for the winter, and I'.arkow has 

 described a portion of this as the ' hibernating 

 gland.' In this special organ, he claims, the fat 

 is transformed into a store of animal starch and 

 sugar, by which the heart and muscles are fed 

 during the period of torpidity. But his oliserva- 

 tions have not been confirmed, this gland not 

 existing in all hibernators ; nor is it at all certain 

 that such is its use. Moreover, contrary to hi.s 

 assertion, hibernators do lose weight, often to the 

 extent of 30 and 40 per cent., in this respect resem- 

 bling starving animals. 



Hibernation in other animals has not been so 

 closely studied. All reptiles and batrachia become 

 torpid during cold weather, snakes passing the 

 winter in tangled knots as if for warmth : if the 

 viper is aroused at this season its venom is said to 

 be inert. Alligators creep into holes in the river- 

 banks, and frogs lie dormant in the mud at the 

 bottom of ponds. Many fishes (carp, roach, chub, 

 minnows, eels, the Mediterranean nmrrena, &c. ) 

 also retire into some deep recess, or into the 

 mud, though their condition at this period is not 

 that of the true hibernators. Their vitality only is 

 lowered. In winter all land-snails hibernate by 

 closing the mouths of their shells with a plate 

 ( the epiphragm ), leaving only a little hole in the 

 middle of it for breathing. Slugs also become 

 torpid in holes in the ground, and the fresh-water 

 mussels (Unio, Anodonta, Dreissena) bury them- 

 selves in the pond and river mud until the cold 

 months are over. The torpidity of insects in the 

 pupa and other stages is well known. Individuals 

 belonging to the Vanessa group of butterflies which 

 hibernate in the imago stage occasionally emerge 

 during mild winter days. But hive-bees do not 

 hibernate, food being necessary for their subsist- 

 ence during the flowerless season. 



See ANIMAL HEAT and PHYSIOLOGY; TEMPERATURE 

 OF THE BODY ; also Barkow's fJer Winterschlaf nock 

 scinen Erscheinuruien im Thierreich danjestellt (1846); 

 Friedleben's Die Phys. der Thymus Driise ( 1866 ) ; Simon's 

 Physiological Essay on the Thymus Gland ( 1845) ; Lloyd's 

 Field Sport* of the North of Europe ( 1885), pp. 124-125 ; 

 Marshall Hall in Todd's Cyclopaedia of Anatomy MM 

 Physiolo(ty (vol. ii. p. 771 et seq.); Newport, Philosophi- 

 cal Transactions (1837); Brown's AI animal* of Green- 

 land (Admiralty Manual, 1875, p. lt>); and Our Earth 

 (1890), voL iii pp. 2t>-30; Duns in Science for All (voL 

 v. p. 240). &o. 



II ilu'rnia. See IRELAND. For the Hibernian 

 School, see ROYAL MILITARY ASYLUM. 



Hibiscus, a genus of plants of the natural 

 order Malvacew, the type of a tribe or sub-order 

 distinguished by a double calyx and fruit of three 

 or more many -seeded carpels united into a many- 

 celled capsule. The species are numerous, natives 

 of warm climates, some of them trees or shrubs, 

 but most of them large herbaceous plant-, annual 

 or perennial. The flowers of many are very beauti- 

 ful ; in the South Sea Islands they are much used 

 for personal adornment. 11. synacius, sometimes 



