Year: 1878

The chief popularity of birds is their
power of flight, and, although there are
few birds which do not fly, most of
them do, and the various organs of their
bodies are all constructed in such q way
as to fit them for life in the air. Their
bodies are very solid and compact, in
order that most of their weight shall be
near the place where the wings are at
tached. The feet, legs, head, and neck
are light, and so arranged that they may
be drawn up close to the body while the
bird is flying. AS the neck is long and
very flexible, the body does not need to
be plant, as with most creatures hav-
ing backbones; but it is important that
the wings should have a firm support,
SO the bones of the back are united.
The body of bird must also be we'll
protected from the cold for, as it as
eends and descends through the air, it
passes through regions of very different
temperatures, and it must be provided
with thick and warm covering in
order to be able to endure these sudden
changes, and one also which shall be
very light and able to shed the water;
for, otherwise, bird would be unable
to fly. The feathers of bird answer
to all these needs, and are SO placed
upon the body that they form smooth
surface which does not catch against the
air when the bird is passing through it.
In its rapid ascents and descents, the
bird is exposed to another danger even
greater than the sudden changes of tenn
perature. You all know that air
presses in every direction with great
force, and that we do not feel it because
there is air in all parts of our bodies as
well as outside them, and the pressure
of the air inside exactly balances that
of the outside air. If we should sud-
denly take away the outside air in any
way, such as covering person up with
an air-pump receiver, and quickly and
completely exhausting the air, the con-
sequences of the inside pressure would
be very terrible, and if the experiment
could be tried quickly enough the body
would burst like an exploding gun,
with a loud noise.


When people go up rapidly in bal
loon, or climb very high mountains,
they are troubled by ringing noise
and feeling of great pressure in the
ears and head, and by palpitation of the
heart, bleeding at the nose, and faint
ing. These unpleasant and often dam
gerous symptoms are caused by the ex-
pansion of the air inside their bodies.
In ascending very high mountains it is
necessary to go very slowly and to stop
very often, to give time for some of the
expanded air to escape, and equalize the
/ ,r1e
condor, for example, fly over the tops of
the highest mountains, and nearly all
birds, either occasionally or habitually,
ascend to very great attitudes, and, un-
less there were some plan for regulating
the pressure of the air inside their
bodies, they would suffer great incon-
venience and pain and danger. But
they are provided with an arrangement
by which the air within them can escape
easily as it expands and thus keep the
pressure within just equal to that out
side, so that they can ascend and descend
as rapidly as they wish, without feeling
the least inconvenience. In the body
of the bird there are several large bags,
like the lungs, called air-chambers
many of their bones are hollow, and
others are pierced with long winding
tubes called air-tubes. All these air.
chambers and air-tubes are connected
with the lungs so that air can pass into
and out of them at each breath. The
connection between these chambers and
the lungs is so complete that wounded
hawk can breathe through a broken
wing almost as well as through its
mouth. When bird mounts upward,
the air inside its body gradually ex
pands, but the bird does not feel any in
convenience; for, at each breath, part
of the air passes from the air-chamber!
into the lungs, so that the pressure OF


the inside does not become greater thai
that of the outside.