Torpidity appears also in some cases to depend on the state of the constitution. Thus, in the same chambers, one marmot shall continue awake and active, while the others are in a profound lethargy. A hedgehog, during the winter season, becomes torpid upon the application of cold ; but, during the summer season, or after the geriod of reviviscence, it resists the sedative effects of that agent. Mangili took a hedgehog, og, the 21st June, and placed it in a temperature of 8° of Ilraumur. It first rolled itself up ; afterwards lifted its head and tried to.escape. Its re spiration became frequent and painful. At the end of the first hour, respiration had become feeble; at the end of an hour and a half, it had ceased to respire ; and twenty minutes after, it was frozen to the heart. When ex amined in this condition, the flesh was found white, the veins of the neck were much swollen, and a small quantity of extravasated blood was observed in the brain and the lungs. It appears probable, that, during tor pidity, the constitution experiences a change something similar to ordinary sleep, by which its exhausted energies are recruited, and it becomes better able to resist the effects of those ordinary agents with which it has to contend.
There are sonic circumstances in the history of these tor pid animals which seem to indicate, that they possess the power of becoming torpid at pleasure, even in the absence of those disposing circumstances which we have enume rated. Spallanzani has seen bats in a torpid state even during summer, and supposes, that as these animals ap pear to possess some voluntary power over respiration, this torpidity may be some instinctive propensity to pre serve life. Mangili, in spring, when the Cricctus g-lis was awake, and when the temperature of the air was between 66° and 68°, placed it in a vase along with nuts and other food. The animal attempted to escape, and refused to eat. It then became torpid. In this state the number of its re• spirations diminished. Instead of rolling itself up as usual before becoming torpid, it lay all the while upon its back, and remained in that state until the 17th of July.
By some it has been supposed, that the fat accumulated in torpid animals during the winter is another of those causes which produce this lethargy. The circumstance is certainly very common, but no direct experiments have hitherto been performed to warrant the conclusion. Spal lanzani has indeed asserted, that among the dormice which he caught for his experiments, some were very fat, while others were lean, and yet they were equally susceptible of torpidity from the action of cold. All this may be the case; but there is certainly reason to believe, that these animals stand in need of some previous store of nourishment to enable them to support that gradual waste which takes place during the period of their slumbers.
Before concluding our account of torpid quadrupeds, it may be proper to add a few observations on their reviviscence.
When the hamster passes from his torpid state, he exhibits several curious appearances. He first loses the rigidity of his members, and then makes profound respirations, but at long intervals. His legs begin to move ; he opens his mouth, and utters rattling and disagreeable sounds. After continuing this operation for some time, he opens his eyes, and endeavours to raise himself on his legs. All these movements are still unsteady, and reeling like those of a man in a state of intoxication ; but he repeats his efforts till he acquires the use of his limbs. He remains fixed in that attitude for some time, as if to reconnoitre, and rest himself after his fatigues. His passage from a torpid to an active state is more or less quick, according to the tem perature. It is probable that this change is produced im perceptibly when the animal remains in his hole, and that he feels none of those inconveniences which attend a forced and sudden reviviscence. • It is evident, from the situations which some torpid ani mals occupy, that they must experience, in the course of their lethargy, considerable changes of temperature. It would form a very curious subject of inquiry, to ascertain the superior and inferior limits of this torpid state with respect to temperature. The Cricetus glie has been observ ed dormant from 34° to 48' ; the dormouse from 27° to 66° ; the marmot from 40° to 51°; and the hedgehog from 26° to 56°.
It is certainly very difficult to account for the torpidity of those animals, which, like the marmot and hamster, con gregate and burrow in the earth. Previous to their be coming torpid, a considerable degree of heat must be ge nerated, from their numbers, in their hole; and besides, they are lodged so deep in the earth, as to be beyond the reach of the changes of the temperature of the atmosphere. Their burrow, during the winter season, must preserve a degree of heat approaching to the mean annual tempera ture of the climate. If this is the case, how is reviviscence produced in the spring ? It cannot be owing to any change of temperature, for their situation prevents them from ex periencing such vicissitudes. Is it not owing to a change which takes place in their constitution ? and, is not awa kening from torpidity similar to awakening from sleep A similar remark may be made with regard to bats in their winter quarters. The caves to which they resort ap proach at all times the mean annual temperature. A few individuals, not sufficiently cautious in choosing propel retreats, are sometimes prematurely called into action, at a season when there is no food, so that they fall a prey to owls, and the cold of the evtning. But what indications of returning spring have those who are attached to the roofs of the deeper caves ? Surely no increase of temperature. Perhaps an internal change is the cause which again ex cites to action.