III. Of perfect hibernation.—I now proceed to treat of perfect hibernation, of its causes, and of its effects on the various functions which I have enumerated. My observations will con sist principally of a detail of a series of obser vations and experiments made in the course of the year compared with the results obtained by other inquirers.
I consider that there is one special cause of hibernation,—that law imposed by the Creator, according to which all animals become affected with sleep at some period of each revolving day, and the hibernating animal at some period of the revolving year. We have thus presented to us the phenomena of diurnal and nocturnal animals, and the winter-sleep and the summer sleep of hibernating animals.
Exposure to cold, not too severe, disposes to hibernation, as it disposes to ordinary sleep. Severe cold, on the contrary, first rouses the hibernating animal from its lethargy, and then plunges this and all animals into a state of fatal torpor.
The absence of every kind of stimulus or ex citant, and a somewhat confined atmosphere,* also conduce to hibernation.
Every excitement, on the contrary, that of hunger, that of the sexes probably, tend to dis turb this peculiar lethargy. It is in this man ner that we explain the periodicity of sleep and hibernation, though there is probably also some hidden influence of the seasons, of the day or of the year, influences which have been traced by Dr. Prout and by M. Edwards in regard to the quantity of respiration.
I now proceed to treat of the condition of the several functions in hibernation.
The process of sanguification is, in some hibernating animals, nearly arrested ; in others, it is entirely so.
There is much difference in the powers of digestion, and in the fact of omitting to take food, in the hibernation of different animals. The bat, being insectivorous, would awake in vain ; no food could be found : the hedgehog might obtain snails or worms, if the ground were not very hard from frost: the dormouse would find less difficulty in meeting with grain and fruits. We accordingly observe a remark able difference in the habits of awaking from their lethargy or hibernation, in these different animals.
I have observed no disposition to awake at all in the bat, except from external warmth or excite ment. If the temperature be about 40° or
the hedgehog, on the other hand, awakes, after various intervals of two, three, or four days passed in lethargy, to take food ; and again re turns to its state of hibernation. The dor mouse, under similar circumstances, awakes daily.
Proportionate to the disposition to awake and take food, is the state of the functions of the stomach, bowels and kidneys. The dor mouse and the hedgehog pass the faeces and urine in abundance during their intervals of activity. The bat is scarcely observed to have any excretions during its continued lethargy.
In the dormouse and the hedgehog, the sense of hunger appears to rouse the animal from its hibernation, whilst the food taken conduces to a return of the state of lethargy. It has already been observed, that there are alternations be tween activity and lethargy in this animal, with the taking of food, in temperatures about 40° or Nevertheless, abstinence doubtless con duces to hibernation, by rendering the system more of the influence of cold, in inducing sleep and the loss of temperature. The hedgehog, which awakes from its hibernation, and does not eat, returns to its lethargy sootier than the one which is allowed food.
The respiration is very nearly suspended in hibernation. That this function almost ceases, is proved, 1st, by the absence of all detectible respiratory acts ; 2dly, by the almost entire ab sence of any change in the air of the pneuma tometer; 3dly, by the subsidence of the tem perature to that of the atmosphere; and 4thly, by the capability of supporting, for a great length of time, the entire privation of air.
1. 1 have adopted various methods to ascer tain the entire absence of the acts of respiration. I placed bats in small boxes, divided by a par tition of silk rihand, the cover of which con sisted of glass, and in the side of which a small hole was made to admit of placing a long light rod or feather under the animal's stomach. The least respiratory movement caused the extremity of this rod to pass through a considerable space, so that it became perfectly apparent.