CHAPTER XII.

SLEEP FROM COLD.

THIS kind of sleep is so peculiar, that it requires be considered separately. The power of cold in occasioning slumber, is not confined to man, but pervades a very extensive class of animals. The hybernation, or winter torpitude of the brown and Polar bear, results from this cause. Those animals continue asleep for months; and do not awake from their apathy till revived by the genial temperature of spring. The same is the case with the hedgehog, the badger, the squirrel, and several species of the mouse and rat tribes, such as the dormouse and marmot: as also with the land tortoise, the frog, and almost all the individuals of the lizard, insect, and serpent tribes. Fishes are often found imbedded in the ice, and, though in a state of apparent death, become at once lively and animated on being exposed to heat. "The fish froze," says Captain Franklin, "as fast as they were taken out of the nets, and in a short time became a solid mass of ice, and by a blow or two of the hatchet were easily split open, when the intestines might

be removed in one lump. If, in this completely frozen state, they were thawed before the fire, they recovered their animation." Sheep sometimes remain for several weeks in a state of torpitude, buried beneath wreaths of snow. Swallows are occasionally in the same state, being found torpid and insensible in the hollows of trees, and among the ruins of old houses during the winter season; but with birds this more rarely happens, owing, probably, to the temperature of their blood being higher than that of other animals, and thereby better enabling them to resist the cold. Almost all insects sleep in winter. This is particularly the case with the crysalis, and such grubs as cannot, at that season, procure their food. In hybernating animals, it is impossible to trace any peculiarity of structure which disposes them to hybernate, and enables life to be sustained during that period. So far the subject is involved in deep obscurity. According to Dr. Edwards, the temperature of such animals sinks considerably during sleep, even in summer.

Want of moisture produces torpor in some animals. This is the case with the garden snail, which revives if a little water is thrown on it. Snails, indeed, have revived after being dried for fifteen years. Mr. Baucer has restored the vibris tritici (a species of worm) after perfect torpitude and apparent death for five years and eight months, by merely soaking it in water. The furcularia anostobea, a small microscopic animal,

may be killed and revived a dozen times by drying it and then applying moisture. According to Spallanzani, animalculi have been recovered by moisture after a torpor of twenty-seven years. Larger animals are thrown into the same state from want of moisture. Such, according to Humboldt, is the case with the alligator and boa constrictor during the dry season in the plains of Venezuela, and with the centenes solosus, a species of hedge-hog found in Madagascar; so that dryness as well as cold, produces hybernation, if, in such a case, we may use that term.

The power of intense cold in producing sleep, is very great in the human subject, and nothing in the winter season is more common than to find people lying dead in fields and on the highways from such a cause. An overpowering drowsiness steals upon them, and if they yield to its influence, death is almost inevitable. This is particularly the case in snow-storms, in which it is often impossible to get a place of shelter.

This state of torpor, with the exception perhaps of catalepsy, is the most perfect sleep that can be imagined: it approaches almost to death in its apparent annihilation of the animal functions. Digestion is at an end, and the secretions and excretions suspended: nothing seems to go on but circulation, respiration, and absorption. The two former are extremely languid,* but the latter

* The extremely languid, or almost suspended state of these two functions, is demonstrated by the fact, that an animal in a

tolerably vigorous, if we may judge from the quantity of fat which the anima lloses during its torpid state. The bear, for example, on going to its wintry rest, is remarkably corpulent; on awaking from it, quite emaciated; in which state, inspired by the pangs of hunger, it sallies forth with redoubled fury upon its prey. Life is sustained by the absorption of this fat, which for months serves the animal as provision. Such emaciation, however, is not common to all hybernating animals, some of whom lose little or nothing by their winter torpitude.

Hybernation may be prevented. Thus the polar bear in the menagerie at Paris never hybernated; and in the marmot and hedge-hog hybernation is prevented if the animals be kept in a higher temperature. It is also a curious fact, that an animal, if exposed to a more intense cold, while hybernating, is awaked from its lethargy. Exposing a hybernating animal to light has also, in many cases, the same effect.

Some writers, and Buffon among the rest, deny that such a state of torpor as we have here described, can be looked upon as sleep. This is a question into which it is not necessary at present to enter. All I contend for, is, that the state of the mind is precisely the same here as in ordinary sleep-that, in both cases, the organs of the senses and of volition are equally inert; and that though

state of hybernation may be placed for an hour in a jar of hydrogen without suffering death.

the conditions of the secretive and circulating systems are different, so many circumstances are nevertheless identical, that we become justified in considering the one in a work which professes to treat of the other.

In Captain Cook's first voyage, a memorable instance is given of the power of intense cold in producing sleep. It occurred in the island of Terra-del-Fuego. Dr. Solander, Mr. Banks, and several other gentlemen had ascended the mountains of that cold region, for the purpose of botanizing and exploring the country. "Dr. Solander, who had more than once crossed the mountains which divide Sweden from Norway, well knew that extreme cold, especially when joined with fatigue, produces a torpor and sleepiness that are almost irresistible. He, therefore, conjured the company to keep moving whatever pain it might cost them, and whatever relief they might be promised by an inclination to rest. Whoever sits down,' said he, 'will sleep; and whoever sleeps, will wake no more.' Thus at once admonished and alarmed, they set forward; but while they were still upon the naked rock, and before they had got among the bushes, the cold became suddenly so entense as to produce the effects that had been most dreaded. Dr. Solander himself was the first who felt the inclination, against which he had warned others, irresistible; and insisted upon being suffered to lie down. Mr. Banks entreated and remonstrated in vain; down he lay upon the ground,