Tell me, my dear child, when you have seen birds taking their flight
into the air, and going boldly to their object, without a thought of
all the barriers, ditches, rivers, and mountains, which hinder man at
every step in his travels, did it never strike you to wish for their
wings, and imagine how you would fly off if you had them? If you ever
dreamt this dream, do not apologise for it; it is one as old as the
world. 'Oh that I had wings like a dove!' cried the Prophet, nearly
3,000 years ago; and the dialogue of the swallow and the prisoner, so
often sung by poets, has been repeated in prose behind all the
prison-bars on the globe since prisons were first invented.
Now you will not think it kind on my part, but I must undeceive you
about this fancy, as you will be undeceived some day about many others.
The wings of a dove or swallow would be of no use to you if you had
them, any more than the formidable swords of the middle ages would be
to our modern gentlemen, were any one to put such into their hands.
We are not adapted for them, nor they for us.
You saw, some time ago, what an amount of muscular exertion was required
for running--what a violent flow of blood, what hurried play of the
lungs. Now in flying it is still worse; for the earth, at any rate,
holds us up quite naturally, whereas the air will not hold up the bird
unless it is beaten vigorously and unremittingly by an untiring wing.
If we men, constructed as we are, had to do such work, we should be
out of breath at once; the heart would cry out immediately for quarter,
and the diaphragm turn red with anger. And only just imagine in what
a critical position a poor wretch launched into the air on the wings
of a swallow would find himself when, at the end of five minutes, his
servants should refuse point-blank to go on working at a height of 500
feet above the ground!
But a bird has not these internal rebellions to fear. In the first
place, it has no diaphragm; so here is another friend to whom we must
say good-bye. We shall not meet with him again anywhere. The journey
we are taking together, my dear, is somewhat like the journey of life.
One sets off, surrounded by friends and acquaintances, but whoever
travels on to the end is apt to find himself alone at last; this is
what is happening to the digestive tube, which we shall see losing all
its accessories, one by one, as we gradually advance in our study.
Even now here is one essential fundamental difference in the internal
machinery. The body has only one compartment instead of two; and the
lungs, masters of the whole space, extend freely to its utmost depths.
When a fowl is cut up at table, look along the body, and you will find
lodged in the cavity of the ribs, a long, blackish, and spongy mass:
this is the lungs. There is not, therefore, the same danger of a bird's
getting out of breath as with us; that delicate board which is found
in our bellows is wanting in his. His is set in action solely by the
to-and-fro movement of the ribs, which is produced by muscular
exertions, which are greatly increased during the action of the wings.
From which it follows, that the rapidity of flight itself regulates
the arrival of air, and consequently the expenditure of strength, or,
if you like better, the activity of the fire, since the energy of the
muscles depends, as we have seen, upon the quantity of oxygen that
feeds the internal stove.
This is not all. These elongated lungs are still not sufficient to
furnish the blood with all the oxygen demanded by this excessive labor
of flight. They are pierced with holes, through which issue pipes which
carry the air all over the body. You know what is said of
spendthrifts?-that they burn the candle at both ends. It is so with
the blood of birds. That fillip which in our case it receives in the
lungs, and which sends it back full of vigor into the arteries, is
repeated in the bird at the other end of the arteries as well. The
capillaries, those delicate vessels at the end of the arteries, plunge
from all sides into little reservoirs of air-lungs, therefore-where
the blood renews its provision of oxygen, and relights its
half-extinguished fire, so that it sends the combustion afresh into
the muscles on its return back to the heart, and sets them going a
second time.
The natural consequence of this prodigality of combustion is, that
there must be, in proportion, much more oxygen in birds than in us;
and that of all animals a bird is the one most quickly poisoned by his
own carbonic acid when the air is not renewed around him. Therefore,
let me beg you never to think of putting a poor little bird under a
wine-glass, as a child of my acquaintance once did, that she might
examine her little friend more closely. In the twinkling of an eye he
would consume all the oxygen inside his prison, and you would soon see
him fall upon his side and die.
On the other hand, the temperature of these flying machines, which
consume so much oxygen, is very much higher than ours. It rises to
41°, 42° (centigrade), and sometimes to 44°, 7° higher than with us.
If ever you have taken hold of a little bird, you will have remarked
how warm it makes your hand: this is quite natural, since there is
always a double fire going on within him, to meet the extraordinary
expenditure of strength that is required of him whenever he takes wing.
Besides, do but look at the poor little creature when you have
imprisoned it in a cage! How it goes up! How it comes down! How it
hops from one perch to another, with a quick sudden movement, like
that of a spring when it unbends. There is no apparent cause for this
state of continual agitation; and yet there is a cause, and only too
serious a one. Its fire is not slackened because you have put it into
a cage, and its muscles, lashed furiously on by the double-oxygenized
blood, drive it hap-hazard into a thousand movements, in which it
expends, as best it can, a superabundance of power, which no longer
finds natural employment. Little children, who are the real
singing-birds of our homes, and whose blood also drives much more
energetically along than ours--little children I say--often fare no
better than caged birds in those larger cages we call schools; and
schoolmasters and governesses would scold rather less if they thought
rather more about this. It is right, I do not deny it, that the
rebellious young rogues should be taught in good time not to abandon
themselves, like wild birds, to the mere animal impulses of the blood:
but, in dealing with them, one must also make allowances, as they say,
for the fire within, and know how to open the cage now and then. It
is not for you, however, that I say this, young lady: you are no longer
a little child; but it may happen that you may have some to take care
of some day. Believe me, then, you must not expect too much wisdom
from them, and you must allow them to change their perch every now and
then. It is a law of our Almighty Father that little children, and
little birds, should not stay too long in one place.
The mechanism of the circulation is here the same as with us, and does
not offer any important peculiarity. Only the left ventricle of the
heart has walls of extreme thickness, which enable it to launch the
blood into the members with greater vigor and rapidity; and the blood
itself, although it is composed of precisely the same materials as
that of the mammals, differs from it nevertheless as regards the
globules. In the first place, they are more numerous; secondly, they
are larger; and finally, instead of being round like a plate, they are
drawn out ovally, and are almost shaped like those long dishes on which
fish is usually served. I shall not attempt to give you the reason of
their size and form. This is hidden from us in the same mystery which
envelopes all the microscopic population of the blood; but is it not
a curious thing, this strange persistency of form in the globules ofall
animals of one class? In all birds they are oval; in all mammals
they are round. In all? Nay, I am wrong. As if the better to hide from
us the key to this riddle, nature has amused herself by making an
exception. Camels and llamas, I forgot to tell you, have also globules
in the form of long dishes, like the hen and the chaffinch. Find out
why, if you can. As to the reason of the number, it is a very simple
one. Since the energy of the blood resides in the globules, it follows
that the most energetic blood will contain the largest amount of
globules. Looking at you, for instance, little monkey, running and
jumping about the garden, I would lay a wager, without counting first,
that there are, in one drop of your blood, some millions more globules
than in one of mine.
Let us now go on to the digestion, with which, properly, we ought to
have begun; but I preferred pointing out to you, first, the particular
character which is the chief mark of distinction in the organization
of the bird.
'When hens grow teeth,' says a shrewd proverb, meaning of course,
_never_. Birds have no teeth, and in this respect there is no
variety among them. All, from the first to the last, have uniformly
the same tool to eat with--the bill, that is--which is, in all cases,
composed of the same elements, two jawbones elongated to a point, and
clothed in a horny armour, which makes their edges sharp and cutting.
At the same time were we to review the birds in detail, as we have
done the mammals, you would see that there are almost more modifications
to be observed in this one single instrument than in our thirty-two
teeth. All birds have a beak, but each has his own, organized expressly
with reference to the kind of food needed by its owner. The eagle's
beak, which mangles living prey, is pointed, bent, and hard as steel;
the bill of the duck, which laps up water from ponds and puddles, in
order to get worms and half-decomposed refuse out of it, is soft, and
flattened like a shovel. The woodpecker's, which has to pierce the
trunks of trees, is like a pickaxe; that of the humming-bird, which
has to suck up the juice of flowers from the bottom of their corollas,
is slender as a needle. The swallow feeds on flies, which it snaps up
on the wing, and has a soft bill, which opens like a little oven. The
stork picks up reptiles in the mud of the marshes; its beak is
straight-pointed, cutting as a knife, and resembles a long pair of
pincers. The sparrow feeds especially on hard grains, difficult to
break; accordingly its beak is stumpy, short, and thick, and is arched
on the upper side for still further solidity. But I should never end
if I began to enumerate all the thousand varieties in the bills of
birds. Each variety, too, corresponds with some peculiar sort of life,
and consequently with a general conformation (easily ascertained) of
the animal in which it appears. Give a naturalist the bill of a
bird--only its bill remember--and he will tell you half its history
without fear of being mistaken.
On the other hand, we must not deceive ourselves as to the real value
of this complaisant bill. Let it transform itself as it pleases into
all manner of forms for the better fulfilment of its task, it makes,
at the best, but a very poor instrument for mastication; nay, to say
the truth, it breaks, cuts, and tears, but it never masticates at all.
Thus the bird's mouthful is far from undergoing as perfect a preparation
as ours does. It is no sooner taken in than it is swallowed, and the
salivary glands, which are still to be found under the tongue, seem
only to be there as a matter of form; what little saliva they produce
is thick and sticky, and has none of the qualities necessary for making
that liquid paste which our tongue sweeps up from every corner of the
mouth. Besides, it must be owned that a bird's tongue would be a very
awkward implement in such a task. Open a hen's bill and you will see
therein a very inferior sort of porter. It is merely a dry hard lance,
as it were, armed with prickles at the point, as ill-qualified for
tasting as for sweeping. So the hen does not waste her time in finding
out the flavor of what is thrown to her. She picks up and swallows
over and over again, without appearing to experience any other pleasure
than that of satisfying her appetite. Birds of prey, it is true, have
rather more convenient tongues, capable, moreover, of tasting up to
a certain point; and the parrot, who is a complete epicure, and chews
his food philosophically, has a charming-little black one, thick,
fleshy, and susceptible--a true porter, in fact-who enables Polly
thoroughly to enjoy her breakfast. But certain birds who live on insects
surpass even the hen in the dryness and hardness of their tongues.
That of the woodpecker, especially, is a model of the kind, and deserves
a few words more than the others. Picture to yourselves a long pin,
terminated by an iron point with barbs like those of fish-hooks. An
ingenious mechanism enables the bird to dart it out with the rapidity
of lightning, far beyond his bill, upon the insects to which he gives
chase. The point pierces them, and the hooks retain them, without any
need of assistance from the bill. I have just told you that this bill
pierces the bark of trees; but it only plays the part of gamekeepers
on grand sporting occasions, who beat the bushes to make the game rise.
The woodpecker's bill routs up the insects by destroying their shelter;
but the real sportsman is the tongue. Good-bye to any notion of a cosy
little chat in such a porter's lodge as that! What could a harpoon
have to say for itself?
Do not, however, let this miserable entrance-hall alarm you, at the
same time, for the fate of the mouthful thus presented half-dressed
to the sophagus. You will find it only so much the better treated
within. In the first place, the sophagus, when half-way down to the
stomach, swells out suddenly and forms a pocket, which is generally
particularly well developed in birds who feed on grain; this is called
the _crop_ in English, in French _jabot_; whence comes the application
of that word to those full shirt-frills which have sometimes been the
fashion. It is the pigeon's _crop_ that gives him the rounded chest over
which he bridles so prettily. The crop is a receptacle where the food
makes a halt: it is something between the pouch of the monkey and the
paunch of the ox; a preparatory stomach, which does not, it is true,
send back the grain to the bill, for the bill could do it no good, but
in which that grain lies until there is room for it further on.
Prom thence it resumes its journey; but, before reaching the true
stomach, it passes through a second enlargement of the oesophagus,
whose walls are pitted with numberless little cavities, from which
pour over it the juices destined to supply the place of the saliva
that was wanting above.
It reaches its destination at last, but still hard, and generally
whole. No matter, however. The stomach which receives it, and which
is called the gizzard, is quite a different sort of thing from a useless
membrane, thin and delicate like ours. It is a thick muscle of enormous
power, lined inside with a kind of horny skin, so tough that nothing
can break through it. You may form some idea of the prodigious strength
of this organ, when I tell you that turkey-fowls have been made to
swallow hollow balls of glass, so thick as not to break when dropped
to the ground, and that at the end of a few days they have been found
reduced almost to powder in the uninjured stomach. No fear of
indigestion with such an apparatus as that. Though the grain may not
have been masticated in the bill, what does it signify? There is a
power here, as you see, quite equal to carrying the whole work through.
Thanks, indeed, to the invaluable horn which lines it, fowls which
have no teeth of their own can safely present themselves with as many
and as hard ones as they please. They swallow small pebbles, which rub
against the grain, during the contractions of the gizzard, and act
just as effectually as if they were fixed in the jawbone. Well, this
terrible gizzard performs its crushing work with such energy, that not
only the grain but the pebbles themselves are ground down there, and
end by being pounded into fine sand. When you rear fowls, do not forget,
if you keep them shut up, to put within their reach a store of small
pebbles, so that they may have teeth to run to in time of need.
You remember the _pylorus_--the porter down below, who keeps the
door of egress from our stomach? He is as badly provided for here as
his fellow-workmen up above; worse in fact. It is a gaping hole, and
we cannot expect a very strict supervision from it. Birds who feed on
fruits profit by this fact to carry vegetables from one country to
another. With such an easy opening, seeds have a good many chances of
passing from the stomach unaltered; and then they drop from the clouds,
as is supposed, hap-hazard, and germinate afterwards, when circumstances
prove favorable, to grow up before the astonished eyes of the natives
into plants of which they have never even heard. The French
Acclimatization Society, which I spoke of lately, and which, though
so modern, has correspondents all over the globe, is at this moment
laboring to effect an exchange between all countries of the natural
productions of their soil. But here you see that nature had thought
of this before, and established her acclimatization society long ago.
To complete the internal work of digestion, so feebly begun in the
bill, an extremely large liver pours torrents of bile into the duodenum,
and the manufacture of chyle proceeds with that wild rapidity which
characterizes all the living actions of birds. But speaking of this
liver, I think I ought to give you an account of a celebrated dish,
considered a great dainty by epicures, called _pâtés de foies
gras_--_fat liver patties_, to translate it into its meaning.
Very likely you will not care to eat them after hearing my story; but
that will be no great loss to you, for it is a very indigestible sort
of food, and not at all good for children.
You remember my telling you about Englishmen going to India and coming
back with a liver-complaint, from having eaten and drunk more than the
climate allowed? By an imitation of this process, human
ingenuity--occasionally so cruel--has created the _pâtés de foies
gras_, the glory of Strasburg. I have been in the country, and can
tell you how it is managed. They shut a goose up in a square box, where
there is just room for his body. They open his bill at feeding-time,
and cram down with the finger as much food as can be got in. This is
throttling rather than feeding it. The poor beast, who can use no
resistance, since it cannot move, and who is kept in the dark to prevent
excitement; the poor beast is quite unable to burn all the mass of
combustibles with which the blood soon finds itself loaded. This carries
them to the liver to be turned into bile; but the liver is not equal
to the work, becomes loaded in its turn by unemployed materials, and
grows and grows, till at last, having filled up all the space around
it, it stops the play of the heart and lungs. When the animal is
nearly suffocated they kill it; and this is how we come to have _pâtés
de foies gras_ to eat! If they give us a fit of indigestion
afterwards, it is a vengeance we richly deserve. At Toulouse, where
the same trade is carried on on a large scale, they used formerly to
go even beyond this. They fastened the goose by the feet before the
fire-place, after having put out its eyes. The imitation of the
Englishman's proceeding was still more perfect here, for the fire acted
the part of the Indian sun to perfection. I do not know that part of
the country well enough to tell you whether they have quite given up
this piece of wicked ingenuity; all I can say is, I devoutly hope so.
The intestine of birds is much shorter than that of mammals. Here
everything is done at full gallop, and the chyle has not to go far
before it is absorbed. I have before me a book, in which I am told
that the wagtails eaten in France can be fattened in twenty-four hours,
if you only know how to set about it, and these birds are not rare;
they belong to the same family as the red-breasts, the tomtits, and
the nightingale. Thrushes and wheatears (ortolans) require, for the
same purpose, four or five days in the same country, left to themselves
to roam about, when the vine keeps open table for them.
This incredible quickness, not only in digesting, but, what is much
more, in transforming food into fresh living material
(_assimilating_ it, as it is called), has often a fatal result
for the bird. He is prohibited from fasting; his life is a fire of
straw, which must be replenished unceasingly, or it will die out in
the twinkling of an eye. Our own little birds--children--eat oftener
than grown-up people, and if by any accident they are kept waiting
awhile, they soon cry out with hunger. You know this, do you not? Well,
then, if any one should give you a bird to keep in a cage, remember
that you have undertaken a great responsibility, and that it will not
do to be careless with him. To neglect feeding him for one day is to
run the risk of finding him starved to death next morning. With this
warning, I will conclude my chapter on birds. I hope I have not spoken
in vain in behalf of those poor little captive songsters, whose fragile
lives are at the mercy of their young masters and mistresses.