Page:Encyclopædia Britannica, Ninth Edition, v. 11.djvu/826

788 HIBERNATION of the animals which hibernate during the winter are liable to fall into a similar state at intervals during mild weather, and Dr Marshall Hall has applied the term " Diurnation " to the day-sleep of bats, which he regards as precisely ana logous to hibernation. MAMMALIA. Although comparatively few mammals hibernate, the phenomena of hibernation and similar con ditions have been better studied in this class than in any other. Dr Marshall Hall has laid down the principle that the amount of respiration is inversely as the degree of irritability of the muscular fibre. Every gradation may be met with between ordinary sleep, the imperfect or abnormal hibernation of some animals, and the profound hibernation of others, in which all the functions of life are almost suspended. Such a condition is always accom panied by reduced respiration, and increased irritability of tho muscular fibre. If the respiration is reduced without this irritability being increased, death results from torpor and asphyxia, whereas, if the respiration is increased simul taneously with increased irritability (as when an animal is aroused too suddenly), death likewise resultsrfrom too great stimulation of the vital powers. The well-known danger of suddenly awakening a patient from a state of somnam bulism is doubtless due to a similar cause. Hibernation, however, is a physiological condition, and not produced simply by cold, though it is favoured by it, because cold induces sleep, which may afterwards pass into hibernation. It is an error to suppose that hibernating animals are capable of resisting any amount of cold, though their capacity of doing so must vary according to their species and to the climate which they inhabit. They always seek secure hiding-places where they may be pro tected from too great a degree of cold, as well as from interference. During hibernation the temperature of their bodies sinks to a point corresponding nearly to that of the surrounding atmosphere ; but if they are exposed to an unusual amount of cold, they are first awakened by it, and then sink into a fatal torpor like other animals. Many hibernating animals perish in this manner during severe winters. Respiration being almost suspended during hibernation, the maintenance of vitality depends almost wholly on the action of the heart, which will continue for a long time after an hibernating animal has been decapitated. Animals may also be placed in carbonic acid or under water for several hours, without injury, when in this condition, though they would die in a very few minutes if they were in their normal state. Man. Long-continued suspension of consciousness in man, whether voluntary or otherwise, is rare in temperate climates, but it is more frequent in India, where some religious ascetics are stated on unimpeachable authority to possess the power of throwing themselves into a state closely resembling hibernation for an indefinite period. Many curious cases have been recorded by Mr Braid in his small treatise on Human Hibernation, published in 1850, the most celebrated of which is that of a fakir who was actually buried alive at Lahore, in 1837, in the presence of Runjeet Singh and Sir Claude Wade, and who was dug up and restored to consciousness several months afterwards, after every precaution had been taken to prevent any one from disturbing the grave in the interval. Bats. Dr Marshall Hall says that the hibernating bat never wakes at all, except from warmth or excitement, and that the digestive functions are suspended to a far greater degree than in the dormouse or hedgehog. Eespiration is also suspended, and when the animal is disturbed it quickly subsides again into total quiescence, after a few feeble respiration?. It is to be regretted that Dr Hall has not stated to which species of bat his remarks refer, as the habits of the various species differ. Earlier or later in autumn, according to the species, they retire to caves, hollow trees, and similar hiding-places, where they cluster together, hanging head downwards by their hinder claws, and clinging to each other, as well as to the walls and sides of their retreat, so that a great number can crowd themselves into an amazingly small space. Although such assemblies frequently consist of more than one species, yet the various species do not all retire to their winter quarters at the same period ; the noctule is rarely seen abroad later than July, whereas the pipistrelle may be seen flying on mild evenings almost every month in the year. It is only natural to suppose that the hibernation of the former s-pecies is much more profound than that of the latter, which doubtless feeds in winter as well as summer ; for though insects are far less numerous in winter than in summer, yet some species appear only at that season of the year. Bear and Badger. These animals retire to winter quarters in northern climates, and pass the greater part of their time in sleep ; but the brovn bear and badger do not fall into a state of genuine hibernation. When the bear retires for the winter, he is very fat, and it is said that the black bear will not hibernate if this is not the case. Digestion is suspended, and his intestines become stopped up with an indigestible mass chiefly composed of pine leaves, which is not discharged till spring. The brown bear of Europe and Siberia is very dangerous if disturbed during the winter; but the black bear of America can scarcely be aroused from his torpor, which there is thus reason to believe is a state of true hibernation, differing from that in which the former species passes the winter. Hedgehog. This animal hibernates more completely than almost any other. In the autumn it retires to a hole among rocks or under the roots of a tree, where it remains for the winter, seldom or never awakening till spring, and of course taking no food until then. If a sleeping hedge hog is disturbed, it merely stirs, and then coils itself up more closely ; but if a hibernating hedgehog is interfered with, it takes a deep sonorous inspiration, followed by a few feeble respirations, and then by total quiescence. The tenrec, an allied animal found in Madagascar, sleeps for three months in its burrow during the hottest period of the year. Bodentia. Several animals belonging to this order hibernate more or less completely, among which we may mention the hamster, the porcupine, the dormouse, the squirrel, and the marmot. Several of these awake at intervals to feed, and therefore lay up a store of provisions before they retire, although they all become very fat before winter. Other species of this order hibernate less perfectly, or only occasionally, like the hare, which will lie beneath deep snow in a small cavity, just large enough to receive her body, for some weeks unharmed. But this is not true hibernation, as respiration is maintained during the whole time, a small air-hole being always kept open by the warm breath of the animal. In a similar manner sheep (though belonging to a very different order of animals) have some times been buried in snow-drifts in Scotland for several weeks without sustaining any injury. The dormouse not only hibernates in the strict sense of the term, but will sleep at intervals for several clays together during mild weather. When a Myoxiis, an allied animal inhabiting Africa, was brought to Europe, it hibernated as if this were its normal habit. Whether it aestivates in its native country is not known, but its hibernating in Europe shows a greater power of adapting itself to changed conditions of life than we should have been inclined to suspect. AVES AND PISCES. It was formerly supposed that various species of swallows hibernated, and it was even

asserted that the sand martin was accustomed to bury itself