HIBERNATION
“Our bats,” continued Uncle Paul, “live exclusively on insects, and
these constitute the hedgehog’s chief food, but it also hunts larger
game or even eats fruit. In winter there are no longer any plump
insects to be had, most of them having died after laying their eggs,
and the few surviving ones having taken refuge from the cold in
hiding-places where they would be very hard to find. The larvæ, too,
the hope of future generations, are lying torpid, far out of sight
under the ground, in the trunks of old trees, snugly hidden away. The
white worm has bored several feet into the ground to escape the frost,
there are no more June-bugs for the long-eared owl, no more
night-flying moths, and no more beetles for the hedgehog. What, then,
is to become of these insect-eaters?”
“They will die of hunger,” answered Jules.
“They would indeed all die, were it not for the providential
arrangement I am now going to try to make you understand.
“You know the proverb, ‘He who sleeps dines,’—a very true proverb in
its simple statement of an undeniable fact. Well, the hedgehog, the
bat, and other animals put the principle into practice with a wisdom
quite equal to that of man. Not being able to dine, for want of
insects, they go to sleep; and so deep and heavy is their sleep that to
designate it we use a special word, lethargy.
“Another proverb says, ‘As you make your bed, so must you lie.’ Our
dumb animals, never lacking in wisdom in ordering their own affairs,
take good care not to forget this proverb, but to adopt wise
precautions before abandoning themselves to their long winter sleep.
The hedgehog chooses for itself a secure retreat amid the great roots
of some old tree stump. Toward the end of the autumn it carries grass
and dry leaves to deposit there, and arranges them in a hollow ball, in
the middle of which it rolls itself up and goes to sleep. Bats assemble
in great numbers in the warm depths of some cavern where nothing can
disturb their slumbers. Heads down and bodies packed close together,
they hug the walls, covering them with a sort of velvet tapestry; or,
clinging to one another, they hang in bunches from the roof. Now the
winter may do its worst and the winds may rage; the hedgehog in its
warm blanket of leaves and the bats in their sheltered caves sleep a
deep sleep until summer returns and with it insects, food, animation,
life.”
“But don’t they eat anything all winter long?” asked Emile,
incredulously.
“Nothing whatever,” his uncle assured him.
“Then bats and hedgehogs must have a secret. For my part, I eat more in
the winter than at any other time, and no amount of sleep would satisfy
my hunger.”
“Yes, the bat and the hedgehog have a secret in this matter. I am going
to tell you this secret, but it is a little hard to understand, I warn
you.
“There is one need before which hunger and thirst are silent, however
great they may be; a need that is never satisfied, and is always making
itself felt, whether we wake or sleep, by night, by day, every hour,
every minute. It is the need of air. Air is so essential to the
maintenance of life that it has not been left to us to regulate its use
as we do in regard to food and drink; and this is so in order that we
may not be exposed to the fatal consequences that would follow the
slightest forgetfulness. Therefore it is with little or no
consciousness on our part and independently of our will that air gains
entrance into our body to do its marvelous work there. On air more than
on anything else do we live, our daily bread coming only second in the
order of importance. Our need of food is felt at only tolerably long
intervals; our need of air is felt unceasingly, always imperious,
always inexorable. Let any one try for a moment to prevent its
admission into the body by closing the entrance passages, the mouth and
the nostrils; almost immediately he is suffocated and feels that he
would surely die if this state were prolonged a little. And what is
true of man is true of all forms of animal life: air is necessary to
them all, from the smallest to the greatest.
“What I am going to tell you now will explain this absolute necessity
for air for the maintenance of life. Man and also every animal of a
superior organization—a classification that includes mammals and
birds—have a temperature of their own, a degree of bodily heat peculiar
to them, a heat resulting from no external conditions, but from the
functions of life alone. Whether under a burning sun or in the freezing
cold of winter, whether subjected to the torrid heat of the equator or
to the glacial climate of the poles, man’s body has a temperature of
thirty-eight degrees, centigrade, and cannot be lowered without danger
of death. The natural heat of birds attains forty-two degrees in all
seasons and in all climates.
“How is it that this heat is always the same, and whence can it come
unless from some sort of combustion? There is, in fact, going on within
us a perpetual combustion, respiration furnishing the necessary air,
and food supplying the fuel. To live is to consume oneself, in the
strictest sense of the word; to breathe is to burn. In a figurative
sense man has long used the expression ‘the torch of life’; but this
figurative term proves to be the exact utterance of the truth. Air
consumes the torch; it consumes the animal no less; it makes the torch
give out heat and light, and it produces in the animal heat and motion.
Without air the torch goes out; without air the animal dies. From this
point of view the animal may be compared to a highly perfected machine
put in motion by heat. It feeds and breathes to produce heat and
motion; it receives its fuel in the form of food and burns it in the
inmost recesses of its body with the help of the air introduced by
breathing. That explains why the need of food is greater in winter than
in summer, the body cooling off more rapidly by contact with the
outside cold air, and consequently an increased consumption of fuel
being required to maintain the normal temperature. A low temperature
creates a desire for food; a high temperature lessens the demand. To
the hungry Siberians hearty food is necessary; they ask for bacon and
other fats, with brandy to drink. But for the people of Sahara a few
dates suffice, with a pinch of flour kneaded in the palm of the hand
with a little water. Everything that lessens the loss of heat lessens
also the need of food. Sleep, rest, warm clothing, all serve to some
extent as substitutes for food. And so there is much truth in the
saying that he who sleeps dines.”
“That may be,” Jules assented, “but I don’t see how hedgehogs and bats
can do without food for four or five months at a time. No matter how
soundly I might sleep, I couldn’t go without eating so long as that.”
“Wait until I finish, and for the present remember this: in every
animal life depends on an actual and never-ceasing combustion. Air, as
necessary to this combustion as to the burning of wood or coal in our
stoves and fireplaces, is taken into the body by breathing. That is
what makes breathing so urgent, so incessant. As to the fuel burned,
that is furnished by the substance of the animal itself, by the blood
made from digested food. Not a finger is lifted by us, not a muscle
moved, that does not use up just so much of the fuel furnished by the
blood, which itself is made by the food we eat. Walking, running,
working, excitement, all forms of exercise or emotion—these literally
burn up our blood just as a locomotive burns its coal in dragging
behind it the immense weight of a train. That is why activity, hard
work, increases our need for food, while rest, idleness, lessens it.
“I will now put to you a question. Let us suppose that there are on the
hearth some burning brands, but that they are few and small, and you
wish to keep the fire as long as possible. Would you let these
firebrands burn freely? Would you take the bellows and blow air on them
to increase the blaze?”
“No,” replied Jules; “that would be just the way to burn up the brands
in no time. They must be covered with ashes. If the air comes to them
very slowly and only a little at a time, they will burn gradually and
the next morning we shall find the coals still alive.”
“That is well said, my boy. To keep up a fire for a long time with a
given amount of fuel, the draft must be reduced, the access of air must
be largely cut off, but not intercepted altogether, because then the
fire would be completely extinguished. Therefore the live coals are
buried under ashes, and if the fire is in a stove the door of the
ash-pit is nearly closed. With plenty of air, combustion is active but
of short duration; with only a little air it is feeble, but lasts a
long time.
“As the maintenance of life is the result of a real combustion, any
animal obliged to endure a long fast, or in other words to dispense
with the regular renewal of the fuel needed in that combustion, must
take into its body as little air as possible. It must reduce the draft
of its furnace. This draft is respiration, breathing; and so, in order
to go without food for months at a time and to make the small amount of
fuel held in reserve in the veins last as long as possible, the animal
has but one course to follow: it must breathe as little as it can
without depriving itself entirely of air, for that would mean the total
extinction of the vital spark, just as the complete cutting off of air
from a lighted lamp means the speedy extinction of its flame. There you
have the hedgehog’s and the bat’s secret for enduring their long fast
through the winter season.
“First of all, every precaution is taken to avoid all loss, all
unnecessary expenditure of heat, and to economize as much as possible
the reserves of fuel in their poor little veins. The hedgehog wraps
itself up warm in a thick blanket of leaves in the heart of a
stone-heap or in some hollow tree trunk, while the bats collect in
compact groups in the warm shelter of a deep cave. But that is not
enough: they must keep quite still, as every movement uses up a certain
amount of heat. This requirement is scrupulously observed: their
immobility is such that you would say they were dead. And yet all this
is still insufficient: respiration must be reduced to a minimum. In
fact, their breathing is so weak that the closest scrutiny can hardly
detect that they breathe at all. This faint remnant of life is not to
be compared, you can well see, to the blazing torch or the brightly
burning fire, both of which, enjoying free combustion, send out waves
of heat and light. It is rather the feeble glimmer of a night lamp
husbanding its last drop of oil; it is the coal that glows faintly
under the ashes. So profound is the torpor, so nearly complete the
inanition, that were it not followed by an awakening this state would
hardly differ in any respect from death.
“The name ‘hibernation’ is given to this temporary suspension of
vitality, or rather this slowing up of life, to which certain animals
are subject during the winter. In the number of hibernating animals, or
animals that indulge in this long winter sleep, are to be included,
besides the hedgehog and the bat, the marmot, the dormouse, the lizard,
serpents of various kinds, frogs, and other reptiles. Do you need to be
told that in order to assume and maintain this torpid condition in
which for whole months food is unnecessary, a special organization is
required? Not every creature can hold its breath at will and thus
escape the necessity of eating. The dog and the cat might sleep ever so
deeply, yet as their breathing would go on almost as actively as in
their waking hours, hunger would arouse them before long.”
“Just as it would me,” said Emile.
“No animals that have an assured supply of food for the winter
hibernate, but those that would otherwise perish with hunger in cold
weather are saved from destruction by the providential torpor that
overtakes them at the approach of the winter season. Their food supply
being cut off, they go to sleep. The marmot is wrapped in slumber while
the turf on the high mountains is covered with snow; the dormouse when
there is no longer any fruit; frogs, toads, snakes, lizards, bats, and
hedgehogs, as soon as there cease to be any more insects to feed upon.”