If the hedgehog in a state of the most perfect lethargy, uncomplicated with torpor, be touched, its respiration is resumed, and it coils itself up more forcibly than before. The dormouse, in similar circumstances, unfolds itself; and the bat moves variously. Not the slightest stiffness is observed. The hedgehog, when roused, walks about, and does not stagger, as has been asserted. The bat speedily takes to the wing, and flies about with great activity, although exhaustion and death may subsequently result from the experiment. The phenomena are similar to those of awaking from natural sleep. Impaired motility, stiffness, lameness, &c. belong to tor por, and not to true hibernation.
III. Of Not the least inte resting of the phenomena connected with hiber nation are those of reviviseence. Hibernation induces a state of irritability of the left side of the heart, which, with high respiration and an arterialized blood, would be incompatible with life. Respiration suddenly restored, and per manently excited, is, therefore, as destructive as its privation in other circumstances.
All those bats which were sent to me from distant parts of the country died. The conti nued excitement from the motion of the coach keeping them in a state of respiration, the ani mal perished. One bat had, on its arrival, been roused so as to fly about. Being left quiet, it relapsed into a state of hibernation. The excitement being again repeated the next day, it again flew about the room; on the suc ceeding day it was found dead.
It is in accordance with this law, that we observe hibernating animals adopting various measures to secure themselves from frequent sources of disturbance and excitement. They choose sheltered situations, as caverns, burrows, &e. secure from the rapid changes and the in clemencies of the weather and season. Many form themselves nests; others congregate toge ther. The hedgehog and the dormouse roll themselves up into a ball. The common bat suspends itself by the claws of its hinder feet, with its head dependent, generally in clusters ; the horseshoe bat (ferrum cquinum ) spreads its wings so as to embrace and protect its fellows.
All these circumstances are obviously de signed to prevent disturbed hibernation.
In the depth of caverns, and other situations sheltered from changes of temperature in the atmosphere, the calls of hunger are probably the principal cause of reviviseence in the spring. The other causes of reviviscence are the return of warmth and external excitements : it is inte resting to observe and trace the gradual return of respiration in the former ease, and of the temperature of the animal in the latter.
If the hibernating hedgehog be touched even very gently, it draws a deep breath, and then continues to breathe for a short time. If this excitement be repeated, the animal is perma nently roused, and its temperature raised. If the temperature of the atmosphere be augment ed, the respiration is gradually excited, and the animal is gradually restored to its state of activity.
If a hibernating animal be excited in a very cold atmosphere, its temperature rises variously, and then fills. A bat was perfectly lethargic in a temperature of 36°. A fine thermometer, with a cylindrical bulb, was introduced into its stomach ; it rose to 39°. One hour after wards, the animal not being further disturbed, the respiration was rapid, and the temperature in the stomach 95°. Shortly afterwards the temperature was 90°. The minute circulation was pretty good, and pulsatory in the arteries, the heart beating from twenty-eight to thirty six times in the minute.
In another bat, in an atmosphere of the tem perature of 36°, the thermometer in the stomach rose to 39°. The animal being continually ex cited, the temperature rose to but speedily fell to The animal excited and revived in this man ner is in a state of exhaustion and inanition. It is incapable of maintaining its temperature if exposed to cold, and will die unless it repass into the state of hibernation. It may be com pared to the ease of the mouse deprived of food in the following experiment of Sir. Hunter. " A mouse was put into a cold atmosphere of 13° for an hour, and then the thermometer was introduced as before ; but the animal had lost heat, for the quicksilver at the diaphragm was carried only to 83°, in the pelvis to 78°.
" In order to determine whether an animal that is awakened has the same powers, with respect to preserving heat and cold, as one that is vigorous and strong, I weakened a mouse by fasting, and then introduced the bulb of the thermometer into its belly ; the bulb being at the diaphragm, the quicksilver rose to in the pelvis to 95°, being two degrees colder than the strong mouse : the mouse being put into an atmosphere as cold as the other, and the thermometer again introduced, the quicksilver stood at 79° at the diaphragm, and at 74° in the pelvis.