That cold is calculated to produce effects similar to tor pidity on man himself, is generally known. When persons in health are irmnersed in salt water at a temperature of the thermometer under the tongue sinks from seven to nine degrees below the standard heat. In a little time, how ever, it recovers its ordinary elevation, and becomes sta tionary. Exposure to cold has also the effect of dimi minishing the force of the pulse very much—of producing great exhaustion, and an accumulation of blood in the ex treme vessels.
But the effects of a reduced temperature on the human system are still better illustrated in the tendency to sleep, produced by a cold atmosphere in certain situations. Those who have ascended to the summits of high moun tains, have, by the exposure to cold, felt an almost irre sistible propensity to lie down and sleep. Dr Solander, while exploring Terra del Fuego, though perfectly aware of the inevitable destruction attending the giving way to this inclination ; nay, though he had even cautioned his companions against indulging it, could not himself over come the desire. When this feeling is gratified, sleep succeeds, the body becomes benumbed, and death speedi ly arrives. How long this sleep might continue without ending in death, were the body defended from the in creasing cold and the action of the air, will probably never be determined by satisfactory experiments. Partial tor por has often been experienced in the hands and feet, which is easily removed by a gradual increase of tempe rature. We may add, that in the case of persons ex posed to great cold in elevated situations en mountains or in balloons, there are other causes in operation which may have a tendency to produce sleep. The previous exertions have reduced the body to a very exhausted pressure of the atmosphere the body is greatly diminished, and the air inhaled by the lungs is rarefied.
When these torpid animals, kept in a confined state, are regularly supplied with food, and kept in a uniform temperature, it has been observed that they do not fall into their wonted lethargy, but continue lively and active dur ing the winter season. This experiment has often been repeated with the marmot and other animals. But when in this state they are peculiarly sensible to cold. Dr Beeves, in some experiments which he performed, says, tt When I was in Switzerland I procured two young mar mots in September 1805, and kept them with the view Or determining. the question, whether their torpidity could be prevented by an abundant supply of food and moderate htz,t. I carried them with me to Vienna. and kept them the whole of the winter The months of October and November were very mild. qty marmots ate every day turnip;, cabbages, and brown bread, and were very active and lively : they were kept in a box filled with hay in a cellar, and afterwards in a room without a file, and did not show any symptoms of growing torpid. De cember the 18th, the weather was cold, and the wind very sharp ; Fahrenheit's thermometer stood at and 20°.
Two hedgehogs died which were kept in the same room with the marmots ; and a hamster died also in a room where a fire was constantly kept, though these animals had plenty of hay and food. The marmots became more torpid than I ever saw them before ; yet they continued to come out of their nest, and endeavoured to escape: the food given them in the evening, wac always consumed by the next morning. In January the weather was unusually mild and warm; my marmots ate voraciously, and were jumping about in the morning ; but at four o'clock in the afternoon I examined them several times, and found them not completely rolled up, half torpid, and quite cold to the touch. They continued in this state of semi-torpor for several weeks longer, never becoming so torpid as to live many days without eating, and never so active as to resist the benumbing effects of the cold weather." Spal lanzani performed similar experiments with the same re sult on the dormouse. He found, that althougb cold to the touch during the day, and completely torpid, that it awoke at night and ate a little, and fell asleep again in the morning-. He shews also that dormice, kept in a situa tion more resembling their wild state, became torpid in the month of November, and remained till the middle of March without eating the food which was placed them.
With some animals, at least, a confined atmosphere ap pears to be indispensibly necessary to the production of torpidity. This is very strikingly illustrated in the case of the hamster. This animal does not become torpid though exposed to a cold sufficient to freeze water, unless excluded .from the action of the air. Even when shut up in a cage filled with earth and straw, and exposed to cold, he still continues awake; but when the cage is sunk four or five feet under ground, and free access to the external air prevented, in eight or ten days he becomes as torpid as if he had been in his own burrow. If the cage be brought above ground, in two or three hours he recovers, and will resume his torpid state when again- sunk under ground. This experiment may be repeated several times, at proper intervals, either in the day time or during the night, the light having no apparent influence. A confined atmosphere, such as the banister requires, does not appear necessary to the torpidity of the hedgehog, the dormouse, or the bat. But exposure to the open air seems to be equally hostile to the lethargic state, in many animals. Mangili always found that marmots awoke when taken from their nest, and exposed to the free action of the air. A current of air he found always to have the effect of producing re viviscence, both with dormice and bats. From these cir cumstances, we perceive the utility of the precautions of those animals in retiring to places where the air is still, and where they may enjoy a confined atmosphere.