THE MAMMALIA—MAN AND BEASTS. 



in" is the order : — The Bat, the Hedgehog, the Dormouse, the Marmot, and the 

 Hamster; the comparison has, we believe, not yet been instituted for the other 

 species. Although there is no precise degree at which these animals lose the 

 faculties of sensation and motion, it has been remarked that the Bats become 

 torpid between the temperatures of 50'^ and 44i^ of Faiirenheit ; the Hedgehog 

 about 44^" ; the fat Dormouse at 41*^. The IMarmot and Hamster cannot become 

 torpid except at a temperature considerably below the freezing point ; and they further 

 require that their respiration should be impeded by diminishing, or altogether pre- 

 Tenting, the accession of fresh air in the boxes or holes where they are confined. 



Absolute torpid'ty can only be said to belong to these animals when their temper- 

 ature has been fully reduced, and their respiration diminished, so that they at 

 length come to be wholly deprived of sensation and voluntary motion. Hyberna- 

 tion is, however, susceptible of different degrees, which are characterized by the 

 number of inspirations made in a given time ; the absence of all respiratory move- 

 ment marks in this case the highest degree of torpidity. All the species do not 

 partake of it in the same degree. The Bats experience a very slight lethargy. On 

 the other hand, the Marmot undergoes the most profound torpidity. 



The pulsations of the heart and arteries become greatly enfeebled during torpidity. 

 In the active state of the Hamster, the heart makes 150 pulsations in a minute, 

 while in its torpidity it beats only 15 times. Bats, during summer, have about 100 

 pulsations in a minute. "When they begin to grow torpid they have only 60 ; and os 

 their lethargy increases, the action of the heart is so feeble that only 14 beats have 

 been distinctly counted, and these were at unequal intervals. Dormice breathe so 

 rapidly when tlioy are awake, that it is scarcely possible to count their pulse ; but as 

 soon as they begin to grow torpid, 63 pulsations may be counted in a minute, 31 when 

 they are half torpid, and only 20, 19, or even 16, when their torpor is not so great 

 as to render the action of the heart wholly imjierceptible — (Reeve's Essay on 

 Torpidity, j 



The results of the recent researches of Dr Marshall Hall regarding the sensibil'ty 

 of hybernating animals are at variance with those of preceding observers. Ac- 

 cording to him, the slightest touch applied to one of the spines of the Hedgehog 

 . immediately rouses it to draw a deep inspiration ; the merest shake induces a few 

 inspirations in the Bat, and the sli|^'i]test disturbance is felt, as appears from its 

 effect in inducing motion in the animal. In fact, he considers the sensibility of 

 these animals during hybernation to be in the same condition as in ordinary sleep. 

 On the other hand, according to I\iI\I. Prunelle, Spalianzani, Mangili, Legallois, 

 and Edwards, the strongest stimuli, with the exception of heat, make no impres-jion 

 upon them. Marmots are not roused from their torpid slate by an electric spark 

 stron" enough to give a smart sensation to the hand, and u shock Iroiii a Leyden 

 phial excited them only for a short time, as Spalianzani relates in his experiments 

 made upon them jointly with Volla. They are insensible to the pricking of the feet 

 and nose, and remain motionless and apparently dead. Bats are insensible also to 

 every kind of stimulus except heat, or to a stream of air blown upon them, whicli 

 affects their sensations powerfully. Wounds have been inllit.tcd, and their limbs 

 broken, without the mutilated animals exhibiting any external signs of pain. 



The internal temperature of these animals during their lethargic sleep chiefly de- 

 pends upon that of the external air, yet it is usually from ot" to T'* more elevated 

 than the latter. Hence their temperature is very variable; it may descend to 37 h^ 

 without changing the state of the animal ; but the internal temperature cannot go be- 

 low 32**, the freezing point of water, without either waking the animal or occa- 

 Eloning its death. 



There exists, therefore, a degree of external cold, which is incompatible with the 

 torpidity or life of these animals. Species which most easily become torpid, such as 

 the Bats, Hedgehog, and Dormice, cannot support an external temperature of 14*', and 

 a heat of tO^ to 54** likewise awakens them. 



They may also be aroused by different mechanical means, such as by shaking them 

 either gently or violently, according to the depth of their torpidity, without it being 

 necessary at the same time to change the degree of external temperature. But if 

 capable of resuming their activity in this way, they cannot long maintain it without 

 the aid of a gentle heat. On being roused from their torpidity, they present all the 

 phenomena of waking from ordinary sleep. When the torpid Hedgehog is touched 

 it coils itself up more forcibly than before. The Dormouse unfolds itself when 

 similailv treated, and the Bat moves variously. There is no stiffness nor lameness 

 in their movements, and the Bat even files about with great activity, although ex- 

 haustion and death are the certain consequences. Dr I^Iarshall Hall thinks that 

 those physiologists who assert the contrary have mistaken the phenomena of torpor 

 ■from cold for a true Hybernation, 



From what has been said, it is evident that the repose of the hybernating I\Iam- 

 maUa is neither uniform nor constant in its duration. As it is influenced by the 

 changes of the atmosphere, it may be continuous or interrupted according to the 

 Tariations of the weather, or the precautions which the animals have taken to shelter 

 themselves from the sudden changes of temperature, as well as their individual sus- 

 ceptibility. 



When these animals are very liable to be awakened, either from their constitution 

 or habits, they instinctively take the precaution of amassing stores of provisions to 

 supply their future wants. The Hedgehog, fur example, has been seen to form seve- 

 ral separate stores, and to resort to them at different periods of the torpid season. 

 Its traces have also been observed upon the snow. 



Wlien torpid animals are suddenly and frequently awakened, their respiration be- 

 comes heightened, and death soon follows. " All those Bats which were sent me 

 from distant parts of the country," says Dr Marshall Hall, "died. The continual 

 excitement from the motion of the coach keeping them in a state of respiration, the 

 animal perished. One Bat had, on its arrival, been roused so as to fly about. Be- 

 ing left quiet, it relapsed into a state of hybernation. The excitement being again 

 repeated the next day, it again flew about the room; on the succeeding day it was 

 found dead. We may thus see one reason of the precautions which these animals 

 take to preserve themselves from being suddenly disturbed or excited. They select 

 sheltered spots, such as barrows or deep caverns, at once stjcure- from their enemies 



as from the inclemencies of the weather. The Common Bat ( VespcrtiUo murmus) 

 hangs itself by the claws of the hinder feet, with the head downwards, while the 

 Horse-shoe Bat (Rhiiiulophus ferrum-equinum) spreads its wings to protect and em- 

 brace its companions. Many other animals form nests, and some congregate together 

 The Hedgehog and Dormouse roll themselves in a ball ;_all which dispositions are 

 evidently intended to preserve them from being disturbed by a low temperature. 



There is no external character by which the hybernating animals can be distm- 

 guished from the others. Though some species belong to the same genus, such as 

 the several Dormice, yet this phenomenon is also found in the Bats belonging to a 

 family, separated by a wide interval, and Comparative Anatomists have sought in vain 

 in the internal structure of these animals for an organization peculiar to them. 



It might, however, be expected, that their organization would approach to that 

 which these animals possessed when in their emljryo state; and this actually 

 happens to a certain extent. A large quantity of fat is lodged in different parts of 

 the body, but especially in the appendages of the peritoneum, which are always more 

 numerous and extensile than in other species. The sub-renal capsules, of whose use 

 we are ignorant, but which we know are mora developed in the fostus than in the 

 adult, are stronger and obtain some growth in these animals of which we are now 

 treating. It is the same with the thymus gland and its appendages ; that is to say, 

 those granulous organs which are found to surround the necks of the torpid animals, 

 such as the Marmots, Dormice, and Bats, and may even extend between both 

 shoulders, as in the Bat, according to the observations of JI. Jacobson of Copen- 

 hagen. Those are nearly all the peculiarities yet observed in the hybernating 

 animals, and they are very far from explaining the causes of this singular phenomenoii. 



Hybernating animals are not found in all orders of the Mammalia. None of the 

 Quadrumana become torpid, probably because none of them are designed to inhabit 

 a cold climate. The order of Carnassiers, on the contrary, contains several, especially 

 among such as reside in cold countries; several are also found among the Rodentia, 

 but the remaining orders do not contain any torpid animals. 



We cannot hy any means agree with M. Edwards in thinking that no species of 

 animal is condemned by its nature to hybernate, and that the sta e of hybernation de- 

 pends upon external circumstances, so that we can make it come and go by regulating 

 the conditions under which animals are placed. On the contrary, we find that the 

 nearer hybernating animals are permitted to approach to their nalural mode of life in a 

 domesticated state, the more they are disposed to follow their natural habits. Tims, 

 torpidity seems perfectly congenial to the nature of the Marmot, and if any animal can 

 be said to be naturally torpid it is this. Although it can live during the whole winter 

 without becoming torpid, it by no means follows from this that its tendency to become 

 torpid is artificial. Wo could no more compel other animals to become torpid on tho 

 approach of » inter, to whom such a stale was unnatural, than we could assign to our- 

 selves a new organ of perception. The circumstance that we have not yet succeeded 

 in referring the phenomena of hybernation to any cause more general than itself, 

 only proves tliat the ultimate cause is complicated and obscure, hut ought not to had 

 us to doubt of its existence. 



In the preceding observations, reference has been made to those species only of 

 whose hybernation there I'an be no doubt. Some species of Bears and Badgere, 

 however, undergo a kind of lethargic sleep, termed quiescence. This state differs 

 liiateria'.ly from that of ordinary hybernation, as the females bring forth their young 

 during their interval of retirement. The common Bear (Ursus arctos) is alwavs 

 loaded with fat in the autumn, when he retires to a den previously lined with branches 

 and soft moss. Here he sleeps but little if tlie winter should be mild, and licks his 

 fore-paws and soles of the feet continually during the intervals of repose ; but when 

 the winter is severe, he sleeps much. This state of quiescence cannot be studied 

 ■nith the same facility as that of hybernation, as these animals never become quiescent 

 when in confinement, but remain as much awake during the winter as in the sprin.r 

 and summer. 



Some writers maintain that the number of animals susceptible of hybernation is 

 •very great ; others ai-e inclined to extend this supposition to all, even to Man himself. 

 Thus, Addison mentions an Englishman who underwent a lethargic sleep from the 

 Sih to the 1 1th of August annually. Sheep in Iceland have been known to live under 

 the snow ; and instances often occur in Cumberland, Westmoreland, and the High- 

 lands of Scotland, of sheep existing for four or five weeks under drifts of snow, where 

 they can procure little or no food, and must, it is supposed, have become torpid. 

 Persons have been known to continue asleep from seven to fourteen days, and some 

 much longer, apparently trom the influence of fear, anxiety, or other causes which 

 tend to weaken the vital powers. Yet these and other instances are far from esta- 

 blishing the fact of torpidity, when we are unable to induce that state in any of these 

 animals, under circumstances which would be certain to bring it on in those predis- 

 posed to hybernate. 



Had JIan not been exempt from that unknown law of Nature which compels certain 

 of the lower animals to become torpid, wo should find it exemplified in all those cases 

 where men have been exposed to cold, and no allusion to such a fact is made in tho 

 history of the human species. Yet Gmclin measured a natural cold of 120° below 

 zero, at Jonislisk, lat. 58° N., long. 110" E., in the year 1735 ; and Pallas, in 1772, 

 found the temperature at Krasnajorsk, lat. 56° N., and 110° E., to be 80° below- 

 zero, so that a mass of quicksilver exposed to the air was frozen and became malleable. 

 The Greenlanders go about with very light clothing, and the Norwegian peasants 

 t\'ork during the winter with their bosoms bare., or roll themselves in the snow. 



It would appear that there are certain animals which experience a corresponding 

 state, that cannot properly be termed hybernation, as it happens during the hottest 

 .months of summer, and in tropical climates. The Tenrecs, or Jladagascar Hedge- 

 hogs {Centenes ecaitdatus), are asserted by Bruguii-re to undergo this summer tor- 

 pidity or Estivation, but his statement has more recently been called in question by 

 Sir Telfair, in an account of that animal. Humboldt, however, has observed this 

 remarkable state in the hottest parts of South America, in certain Reptiles which 

 pass a part of the year buried in the earth, and do not leave their state of torpor until 

 the rainy season drives them from their retreats. The singular state of torpidity, 

 induced by the excitement of a high temperature, may be considered as analogous t» 



