128 HIBERNATION OF THE BATS. 
fact, the animal heat of these creatures is rather high, as is the case with most flying 
beings, whether mammals or birds. 
Many curious and valuable trials have been made upon bats while in a state of 
torpidity, the subjects of experiment being placed im such a manner that the least act of 
respiration made itself clearly visible, by the movements of a delicate index. The wing 
was extended in such a manner, that the circulation of the blood was perceptible through 
its semi-transparent membrane, and a thermometer was arranged so as to register the 
temperature. 
Very great care is requisite in conducting these experiments, because the least 
excitement, or the slightest raising of the temperature, suffices to rouse the somnolent 
animal, and to alter the conditions which are absolutely necessary for true hiberna- 
tion. A hasty footfall, or an accidental tap given to the table on which the creature 
rested, would cause it to make several respirations, and to recover sufficient vitality to 
raise the temperature, and to consume some portion of oxygen from the air. The same 
animal which passed ten hours in a state of perfect somnolence, without producing any 
perceptible effect on the oxygen contained in the atmospheric air, consumed in a single 
hour more than four cubie inches of oxygen, when aroused and lively. 
The curious subject of hibernation will be again noticed in connexion with the various 
animals, such as the marmot, dormouse, and others, which pass the cold months in a state 
of torpidity. 
The analogy that exists between the bats and the birds is too evident to escape 
attention. But the most curious part of the analogy is the order in which the various 
portions of a mammalian animal are modified, so as to discharge the faculties which 
belong more properly to the feathered tribes. 
The elongation of the fingers, and expansion of the membranous “wings,” has 
already been mentioned, as well as the general development of the breast-bone. These 
two structures are in common with all bats, as are their corresponding portions in all 
birds. But there are some organizations which are found greatly developed in certain 
families of birds, and are repeated in certain of the bats. 
The structure to which allusion is here made is that connexion of the lungs with the 
skin, or, rather, with the space between the skin and the body, that is found in many 
birds, especially those which pass a marine existence, and which enables the bird to 
inflate its skin with air, and so to increase its bulk largely without sensibly increasing 
its weight. 
In the birds, this inflation is made by direct communication with the lungs; but in 
the bat, the air is conveyed into the membranous cells after a different fashion. A very 
small opening is found to exist at the bottom of the cheek-pouches of either side, and is 
furnished by an apparatus by means of which the air is prevented from escaping without 
the will of the animal. This opening affords a communication between the mouth of the 
bat and the space between the skin and flesh, which are only tied to each other by a few 
membranous threads at each side of the neck, and on the sides of the thumb. 
When, therefore, the bat desires to inflate its body, it closes its mouth, and forces the 
air from its lings through these cheek-passages into the empty space between the skin 
and flesh. The result of this operation is, that the skin is puffed out on all sides of the 
animal, so that the creature is immersed in a kind of atmospheric bath. So enormously 
is it distended by the amount of air which is introduced, that it loses all its shapely 
proportions, and looks like a little ball of fur, to which the head and limbs had been 
artificially attached. 
The bats which are possessed of this wonderful faculty belong to the genus “ Nycteris,” 
and are found in Africa. What may be the object of so singular a power is not 
satisfactorily proved. That it gives very great buoyancy to the form is evident enough, 
but it also seems plain that it is intended for other designs than the obvious one of 
decreasing the proportionate weight of the animal. 
