The History of a Mouthful of Bread
by
Jean Mace
Part 6 out of 6
basis upon which the Creator of the animal world had raised his varied
constructions?
How would it be, then, if we were to take the insect from its
starting-point when it is only a worm, that is to say, merely and
simply a digestive tube? for I am only telling you a small portion of
its history here; a history you must know, which reveals a miracle
still more wonderful than the transformation of the little tadpole
into the frog! There is a brilliant-colored fly which comes buzzing
about the meat-safe--the bluebottle--do you know her? It is on her
account that we put large covers of iron wire over the dishes of meat;
but, perhaps, you never troubled yourself to think why.
But the truth is, she only comes there to deposit her eggs in the good
roast-meat; and if she could get near enough to do so, you would soon
afterwards see it swarming with little white worms, which would entirely
take away all your appetite. These worms are only flies out at nurse,
and they will find their wings by-and-by if you only give them time
enough. Disgusting as they may appear on a dining-table, I assure you
they deserve more interest than you may think. When we come to speak
of worms, we will ask of them to let out the secret of the mysterious
transformations of animals.
In the meantime, let us finish the observations we were making on the
_perfect insect_, as this little creature is called when he has
passed through the intermediate stages which separate him from the
undeveloped condition. Forgive me, my dear child, here I am speaking
to you as if you were a grown-up woman! This is because it is so
difficult to explain things of this sort in any other way. And now
that you have been introduced into the midst of the wonders of creation,
you ought to familiarise yourself with the ideas and terms they have
suggested to mankind. I began with you as a child, and great would be
my triumph if I could leave you a grown-up girl! And I flatter myself
that I have so far set your brain, to work, under pretence of amusing
you, that this hope is not altogether unfounded. I found it necessary
to say this to you in confidence, because I have just read over our
first conversations, and perceive that I have insensibly put you on
a different diet from the one I began with. I am obliged to comfort
myself by remembering that you have grown older since, and that you
are now acquainted with a great many things which you had never heard
spoken of then. And this is the secret of all transformations. We crept
on at first over ground that was quite unknown to us; but as we went
along, our wings must have begun to grow, and we are now able to fly
a little!
Do not be afraid, however; I will exercise your tiny butterfly-wings
very carefully just at present. We have only to examine what becomes
of the _chyle_ of the cockchafer after it has been prepared in
the pretty little tube so finely wrought. We men have _chyliferous_
vessels which draw up chyle from the intestines and throw it within
a short distance of the heart, into the torrent of blood, where its
education is completed. But the cockchafer, who has no other vessels
than his air-pipes, and the _dorsal tube_, which has no communication
with the intestines, what is he to do? Do not distress yourself about
him. Make a tube of a bit of linen, well sewn together, and fill it with
water. Sew it together as firmly as you may on all sides, the water will
have no difficulty in escaping through the meshes. And this is just what
happens with the little tubes found in animals, the coats of which are
formed of interwoven fibres. By-the-by, from thence comes their name of
"_tissue_," which they share in common with all the solid substances of
the body, for all were once supposed to have the same general structure.
The intestine of the cockchafer floats, did I not say? in the lake of
blood which fills the whole cavity of the body. Well, then, the chyle
has only to penetrate through these coats, to go where it is wanted.
Hence it is not at all surprising that this blood should be white; and I
have very good reasons just now for comparing it to our _chyle_. It is,
indeed, chyle arriving directly from the place of its manufacture,
without undergoing any other process; by which you may see that this
little machine (of the digestive organs of the cockchafer), though
differing in appearance so entirely from our own, is reducible to the
same elements of construction, and that life is maintained by the same
process as with us; namely, by the action of the air upon the albumen
extracted from food. The cockchafer, it is true, is much further removed
from being a fellow-creature of ours than even the horse; but the
principle of life is the same with him as with us. And this is quite
enough to cause children, who can feel and reason, to think twice before
they begin to torture, by way of amusement, a creature whose life the
God of goodness has subjected to the same conditions as our own. I speak
this to those miserable little executioners who make toys of suffering
animals: but the case is different with agriculturists, who have
necessarily to contend with the devourers of their harvests, and whom,
I admit, it would not be reasonable to bind down by the maxim of Uncle
Toby.
[Footnote: I have introduced my Uncle Toby, who really has nothing
to do here, in order to make you acquainted with a few lines of Sterne,
which I wish I could place before the eyes of every child in the world.
"Go!" said he, one day at table, to an enormous fly which had been
buzzing around his nose and had cruelly tormented him all dinner time.
After many attempts, he finally caught him in his hand. "Go! I will
not do thee any harm," said my Uncle Toby, rising and crossing the
room with the fly in his hand; "I would not hurt a hair of your head.
Go!" said he, opening the window and his hand at the same moment, to
let the fly escape; "go, poor little devil; away with you; why should
I do you any harm? the world is certainly large enough to contain both
of us!"]
But now to finish with the cockchafer. We have got to examine one very
important part of his body, that which in other animals has been the
one most talked about ever since we began our study: I mean the mouth.
You know that this is the essentially variable point in the digestive
tube; so that you will not be much surprised, should we find he has
something altogether new. The mouth of the cockchafer is composed of
a great number of small pieces placed externally round the entrance
to the _alimentary canal_; but the names of these, as they would
not interest you, I will not enter upon with you; more especially as
they refer to such tiny morsels, that you would have great difficulty
in finding them again on the owner. Of these pieces only two are worth
our attention. These are two bits of extremely hard horn, placed one
on each side of the animal, which are called "_mandibles_" and
which serve the cockchafer to cut up the leaves which he eats. Fancy
your share of teeth being two huge things fixed in the two corners of
your mouth, each advancing alone against the other till they meet under
the nose! You would then attack your tarts with the weapons of the
cockchafer! You would not, however, be able to bite them straight
through from the top to the bottom, as is done by all the animals whom
we have yet seen. It is this which so peculiarly distinguishes the
insect's manner of feeding; for we have already been taught by the
bird and the tortoise, that it is possible to eat with two pieces of
horn. The cockchafer now shows us how to eat sideways; but this is
merely an accessory detail. It does not affect what happens after the
mouthful is swallowed. All insects, however, have not this peculiarity.
The cockchafer belongs to the category of grinding insects as they are
called, who bite their food: but there is the category of the sucking
insects (or suckers), whose food consists of liquids; and these insects
are furnished in a different manner.
In the innocent butterfly, who lives on the juice of flowers, the
digestive tube terminates externally in a sort of _trunk,_ twisted
in several convolutions, which is nothing more than an exaggerated
elongation of the two jaws, which become hollow within, and form a
tube when joined together. When the insect alights on a flower, he
suddenly unrolls this trunk, and sucks in the juices from the depth
of its "corolla," as you would drink up liquid with a straw from the
bottom of a small vial. Amuse yourself some summer's day by watching
a butterfly in his labors amongst the flowers: sometimes he stops
still, but oftener he is contented to hover over them; and, as he does
so, you will see a little loose thread, as it were, move backwards and
forwards as fast as possible: this is his trunk, which he darts out,
while flying, into the corolla of the flowers, but which scarcely seems
to touch them, so delicate is its approach.
Less inoffensive far is the trunk of the mosquito-gnat, and of all the
detestable troop of blood-sucking flies. It is always a tube; but this
tube is no longer a simple straw, but a sheath furnished with stilettos
of such exquisite delicacy and temper, that nothing is comparable to
them; and these, as they play up and down, pierce the skin of the
victim, like the lancets of the lamprey, and, like them, draw in blood
as they retreat.
Finally, amongst the _parasites,_ the last and lowest group of
insects, the stiletto-sheath is reduced to the size of a kind of little
tube-shaped beak, which, when not in use, folds down like the fangs
of the rattlesnake.
You do not know, perhaps, what a parasite is. The word comes from the
Greek, and signifies literally, "_that which moves round the
corn._" The Greeks applied it to those shameless paupers who, to
escape honest labor, made their way into the houses of the great, and
enjoyed themselves at their expense. These parasites are little animals
which settle themselves on large ones, to suck in, without having
worked for it, the blood which the others have manufactured. The wolf
hunts, fights, and tears its victim in pieces; and then, by means of
that interior labor which I have spent so much time in describing,
transforms it into nourishing liquid: and when all this is accomplished,
the little flea, who lives hidden among his hairs, coolly draws out
for his own use the valuable blood obtained with so much effort. There
are many parasites in the world, my dear child--yourself, for instance,
to begin with--who are perfectly happy to chew your bread without
asking where the corn comes from which made it. But you have heart
enough to see plainly that this indifference ought not to last, and
that it is not honorable to go on living in this indefinite manner at
other people's cost only.
You will some day have duties to fulfil, which you should accustom
yourself to think of now, in order that you may prepare yourself for
them beforehand, so that it may never hereafter be said of you that
you passed through the midst of human society, taking from it all you
needed, without giving it back anything in return, I advise you to
conjure up this idea when the time comes to leave off playing and begin
preparing to be of use. The sort of thing is not always very amusing,
I admit, but you must look upon it as the ladder by which you will be
enabled to rise from the degradation of a parasitical life. If you
were in a well, and some one were to let down a real ladder for you
to get up by, I do not think you would complain of the difficulty of
using it. It is for you, then, to consider whether you would like to
remain for ever in your present condition; for those who learn nothing,
who _submit_ to nothing, who are good for nothing, but to show
off and amuse themselves--these remain parasites all their lives in
reality, however little they may sometimes seem to suspect it.
At your age, however, there is still no disgrace in the matter. God
shows us by the insects that little things are allowed to be
parasitical; but on this subject I must return to a point in the history
of animals which I touched upon before. I told you, in speaking of the
crocodile, that the perfect state of the inferior animals is found
represented in the infancy or less perfect state of those above them:
and I may say the same again with regard to insects. All the young of
the mammalia begin life as parasites, at least, as sucking animals:
for they all live at first on their mother's milk, which is nothing
more than blood in a peculiar state. But the name of parasite among
insects is generally confined to those which take up their abode on
the bodies of their hosts; though in common justice it might equally
well be applied to the gnat and his relations, who, when once full,
make their bow and are off, like the kitten when he has finished
sucking. Well, without meaning to find fault, if we descend to the
lower ranks of the mammals, we shall find among them many parasites
in the received sense of the word. You remember the pouch to which the
marsupials owe their odd name. The young kangaroo remains hidden for
months in the pouch of its mother, feeding continually all the time;
and it is then a strict parasite. During the four following months it
goes in and out, and strolls about between meals, like other young
ones of its class, and is then an animal at nurse affording thus a
twofold example of the tendency of the great Creator to repeat Himself
in His conceptions, here using for the infancy of the mammal the system
invented for adult insects--elsewhere repeating the butterfly in the
humming-bird, who may fairly be called a vertebrated butterfly, and
reproducing the gnat in the vampire-bat, which I look upon as an
enlarged and perfected revise of the original pattern, whence comes
the scourge of our sweet summer nights.
And now, surely, I have said enough about these parasites, whose very
name, I suspect, will make you shudder after my impertinent application
of it. Never mind: it depends entirely upon yourself to get rid of
whatever you find humiliating in the position I have hinted at. Do all
you can to bring happiness to the parents on whom you live at present,
and who give their life-blood so willingly for your good. God has made
you very different from those little animals who have neither heart
nor reason to guide them. Do not be like them, then, in conduct. By
a little obedience and love--child as you are--you can pay them back
what you owe, and they will never complain of the bargain.
LETTER XXXVIII.
CRUSTACEA--MOLLUSCA. (_Crustaceans and Mollusks._)
_Crustaceans._
Crustaceans consist of cray-fish, crabs, lobsters, and prawns, who may
be considered cousins-german of insects, among which more than one
naturalist has thought they ought to be placed. Like them they are
divided into _grinders_, having the same action of the mandibles;
and _suckers_, who are also parasites, and have tubular sheaths
containing stilettos. Mammals and birds are the victims of parasitical
insects; fishes have been reserved for the crustaceans, who do not
disdain also to fasten upon their humble neighbors, the mollusks; and
even among themselves the little ones settle down on the great. A few
live on land, but an immense majority in water, and seem destined to
represent, in the aquatic world, the aerial class of insects, from
whom, however, they differ in many ways.
The first difference is in that stony crust with which they are
enveloped, like the cockchafer in his horny cuirass, and which you
must know well enough if you have ever eaten lobster. Wherever we meet
with horn in insects, we find stone in crustaceans. The jaws are stony,
and the teeth of the stomach also. They are constructed on the same
plan, only the materials are changed.
The digestive tube is less complicated, and consists merely of one
large stomach, instead of that series of stomachs by which insects
approach the organisation of birds. On the other hand, if among some
of them the liver is reduced to simple tubes, floating loosely in the
body, as we have just seen it in the cockchafer among insects, these
tubes are generally so profusely multiplied, and press so closely
against each other, that they form a large compact lump--a true liver,
to sum up all--from which issues, as from ours, a _choledochian
canal_, a bile duct, _i. e._, which passes out into the intestine at the
entrance of the pylorus.
You recollect that canal of the liver which I was afraid to tell you
the name of because it was so ugly? Well, this is that formidable name!
Now that you have swallowed so many others, you must be strong enough
to digest this.
No chyliferous vessels have been found in crustaceans, whence one may
conclude that the chyle leaves the intestine by oozing from it, just
as it does in insects. There it gives rise to an almost transparent
sort of blood, a kind of sap, or lymph, which is put in motion by a
genuine circulation-apparatus; a real heart, with all its canals. This
heart has only one ventricle, and only sends blood in one direction,
as in the case of fishes; but there is an essential difference between
them, which we must point out. The heart of fishes may be called a
venous heart, since it only receives venous blood, which passes thence
to the gills, while that of crustaceans is an arterial heart. It
receives the blood directly it leaves the respiratory organ, and sends
it, not into one aorta, but into several arteries, which set out at
once, each in its own direction, to nourish the various quarters of
the body. This greatly resembles the system of circulation, with which
we are already acquainted. The veins only are unsatisfactory. They
form a kind of transition between the uncertain currents which convey
the blood of insects from one end to the other of the cavity in which
these strange organs lie bathed, and the closed canals of the higher
animals. But they are not canals, properly speaking. The irregular
intervals which separate the organs, more numerous here, are enclosed
by membranes, between which the venous blood pours, and naturally the
chyle also. The whole thus arrives at certain excavations formed at
the place where the legs are jointed on to the body--reservoirs, so
to speak--where the real canals come to carry it off and convey it
away into the gills.
It is, in fact, by means of gills that crustaceans breathe in their
character of aquatic animals. These gills are made nearly upon the
same model as we have already seen in those of fishes; and although
their form and arrangement differ in different species, yet the
principle is always the same: they are tufts of leaflets springing
from stems, up and down which run two tubes; one which brings the blood
from the venous reservoirs, the other which carries it to the heart.
Crabs, lobsters, and crayfish, who are the "file-leaders" of the
crustacean tribe, have gills enclosed in the body, as fishes have; but
the circulation of the water goes in a contrary direction to theirs,
as does that of the blood. Instead of entering at the mouth and going
out at the sides, as we have seen, it enters at the edge of the bony
shell which covers over the body and comes out near the mouth--a merely
accidental detail which does not in any way alter the play of the
apparatus. All these animals are equally adapted for swimming and for
walking, crabs especially, their gills accommodating themselves without
difficulty to contact with the outer air, as we have seen among certain
fishes; so that one might class them with amphibians. There is even one
crab who has acquired the name of _land-crab_, because, although he has
got gills, he dies in water, the small amount of air he can get out of
it at a time being insufficient for him, and who, therefore, lives
constantly on land. It is true that he seeks out damp spots, for his
gills would also fail him if they became parched, and, like the fishes
who make excursions on dry land, he is provided with an internal
reservoir, which is always filled with a certain quantity of water.
Some aquatic crustaceans have the labor simplified by external gills,
which hang down into the water, sometimes depending from the stomach,
sometimes from the legs. In France you sometimes see at a table certain
little animals, very like shrimps (_squillæ_), the bases of whose
hinder legs are fringed by slender tufts, which are in fact their
gills. They find themselves placed there just within reach of the
venous blood; for in the body opposite the bases of the legs are little
cavities in which it accumulates. Now these gills can only act when
under water, and so the squillæ dies as soon as he is removed from
that protecting element. For the same reason they cannot be kept long,
nor travel far, much to the regret of those who like them and live at
some distance from the sea.
There are other crustaceans, next-door neighbors of the squilla, whose
gills are still more simplified. Here the legs themselves are turned
into extremely thin plates, which play the part of gills, and are thus
organs for two purposes, serving at the same time to swim and breathe
with.
We have in our house one little crustacean, the only one I know of who
associates with men, and that is the wood-louse. You must know the
little grizzly beast, which rolls itself up into a ball whenever it
thinks itself in danger, and who would be taken for an insect by anyone
who was not taught otherwise. The wood-louse has neither gills hanging
down outside, nor anything inside her body which resembles the breathing
apparatus of her great relations. But, on examining her closely, you
will perceive all along her stomach a series of little plates, which
are her breathing-organs, and which come under the class of gills,
because, like other gills, they require a certain degree of moisture
to make them act properly. You will never, therefore, see a wood-louse
strutting about in the sunshine, where he would dry up far too quickly;
but if ever you get into a dark, damp corner, there you have every
chance of finding one.
Animals who breathe through their legs and through their stomachs! You
are astonished, and ask, What are we coming to? What would you say,
then, if I were to go really to the depths of the crustacean world?
We should find there such extraordinary beings as you can form no
notion of, for they all live down below in the sea, and have no special
breathing-organ at all, inasmuch as they breathe through the whole
surface of the body. Do not exclaim yet! I will soon show you one whom
you know perfectly well, and who has no other way of breathing.
But we must keep to the higher crustaceans, if we want to judge of the
class. By going too low, we run the risk of not seeing clearly. Animal
creation is here on a system of experiments: and they are so endlessly
multiplied, and exhibit such a profusion both of deceptive resemblances,
and of differences which disappear by transformations, that
classification no longer knows which way to turn. Worms, crustaceans,
mollusks; to which group do these and those belong? To which ever we
like to refer them, for these groups represent nothing definitely
determined in the plan of creation; and though easy to be distinguished
from each other in the higher branches, they become confused together
in the lower, like mountain summits which spring from a common base,
at the foot of which they are all united together.
On this account, my dear child, you will, I am sure, excuse me now and
henceforth, from entering into details of all the horrible beasts which
swarm in the shallows of the animal world, and whom learned men have
in their wonderful wisdom muffled up in terrible names, in order to
prevent children from coming near them! What would you have thought
of the poor little squilla, so prettily baptised by the fishermen, if
I had taught you that it belonged to the order of _Stomatopoda_?
You will scarcely be able to pronounce the word; but that is no fault
of mine, it is spelt so.
We will content ourselves, then, with having taken a glance at the
most clearly marked individuals; and as I said to you just now, it is
by them that we will arrange our inventory of the groups. Here, as you
may have already remarked, instead of continuing to wander from the
original model whose gradual deterioration we have been following all
this time from one class to another, it would seem that we are retracing
our steps, and regaining some portion of the lost ground. This is
because insects, as I have already stated, are an exceptional case--an
idea apart from the great general plan--a by-lane turning off from one
side of the great line of animal creation.
The crustacean, less perfectly worked out than the insect assuredly,
but more regular, forms, so to speak, the connecting line between that
tiny masterpiece of fancy, so incomplete in its exquisite organisation,
and the shapeless but better constituted lump of the mollusk, who
conceals under his heavy shell the sacred deposit of real organs, those
which we expect to find always and everywhere. An insect outside,
though less refined it is true, a mollusk within, the crustacean reminds
me of what among us is called an _amateur_--that mild lover of
the arts who holds a middle place, as it were, between the artist and
the common citizen.
I regret that you are not at present quite able to appreciate my
comparison fully: but put it by, in reserve, if possible, in your
memory; you will find out hereafter how just it is, and it will,
perhaps, help to prevent you from always setting the lively, noisy
artist, above the quiet and silent citizen. Let this, however, be
between you and me. If they could hear us talking, neither artist nor
citizen would forgive me, and the amateur still less.
_Mollusks._
There is one mollusk universally well known--namely, the oyster--so
we will choose him for discussion. To look on one's plate at that
little mass of soft, compact substance, one feels inclined to ask what
there can possibly be in common between it and us; and if you were to
declare that there was not the faintest trace of resemblance between
the organization of the oyster and our own, I should not be surprised.
Wiser people than you have been caught tripping there; not that they
were ignorant of the points in which the oyster resembled us, but they
paid no attention to them. Viewing it in other respects, they declared
that it was of a structure completely different to our own; and that,
in the construction of this machine, the Creator had worked upon a
particular plan, laid aside afterwards as useless for any other purpose.
I should like to get hold of one of those Academicians, with thirty-six
plans, and confound him before you, in proof of his relationship to
the oyster, by showing you at one sitting that there is an oyster in
himself; nay, further, that he is nothing but an oyster, revised,
amended, and considerably enlarged. And do not imagine that I am only
using a figure of speech here, as the professors of rhetoric call it;
which would be in bad taste: I am speaking literally, and to prove the
existence of the oyster in question in our Academician, I shall only
ask permission to perform a slight operation upon him. You exclaim at
this; but do not alarm yourself, for it is only an operation on paper,
he will not die from it. See now, I cut off his head, his two arms,
and his legs; I take out of his body the vertebral column and the ribs;
I gently place what remains between two shells; and ... there is my
oyster. I willingly admit that it is more carefully elaborated and
richer in details than its sisters in the oyster beds; but all the
principal organs are to be found in them also, and they positively are
beings of a similar construction: you shall judge for yourself.
The mouth--for there is a mouth, though one must look closer than the
oystermen do to discover it--the mouth is exactly what the gullet
(oesophagus) would be in a man whose head had been cut off; that is,
a truncated tube. Then comes the stomach, situated in the very midst
of the liver; which latter may easily be distinguished, even by the
most cursory glance at luncheon, from its dark color. The intestine
also goes right through the liver, doubling backwards and forwards
several times: and thus the digestive tube supplies itself with bile
from the cask (to borrow a commercial expression); and this saves the
expense of a bile-duct (choledochian canal), which would be an
unnecessary mode of conveyance in this case. The animal lives in water;
consequently, instead of lungs he has gills: [Footnote: The land-snail
has lungs.] these are those thin, finely-streaked plates which make
a fringe at the very edge of the shell. Finally, on leaving the gills
the blood is received by an arterial heart, with only one ventricle
like that of the crustaceans, in the shape of a small pear, similar
to ours, having an auricle, and an aorta, branching out so as to
distribute the blood throughout the whole body. And now what do we
find here, let me ask you, in this mutilated man, reduced to the soft
portions of the trunk, whom I have been imagining? A heart, with its
arteries; lungs; a liver; an intestine; a stomach and an oesophagus:
that is to say, merely and simply the organs of nutrition. That is
all, or very nearly so.
As you perceive, then, all the elements of our own feeding-machine lie
between the two shells of a mollusk; in a rough state as yet, it is
true; incomplete, and unruly; as in the case of the intestine, for
instance, which in many of these creatures passes without ceremony
through the heart: but even so they are quite sufficiently indicated
to prevent their being mistaken. Now this machine, it is in vain to
deny it, is the animal itself; but it lives at first, and it is this
which dies in it last. The other matter (the locomotive power),
important as it may seem to us in higher races, only holds a secondary
position in reality: the proof of which is, that here is an animal
reduced absolutely to a mere feeding-machine, who still lives, whilst
there yet remains to be found one who has nothing left but his
movement-machine, and who can yet exist. We cannot disown this primitive
animal, for we have it within ourselves; lost, so to speak, in the
midst of the accessory organs which are successively added to it in
proportion as we rise in the animal scale, but still preserving its
own life, its personality, if I may use the expression. Listen to this,
for here is a history well worth hearing.
I will explain to you, hereafter, how all the actions of the
movement-machine are performed by means of a network of nervous threads
(filaments), whose centre of impulsion is in the brain. How our will
acts upon the brain, and gives its orders to the muscles through the
nervous fibres, I will not offer to explain: it is a fact, let that
suffice us. You say to your foot, "Forward!" and off it starts; "Halt!"
and it stops. Here is an organ under command, a servant of the brain,
where we rule ourselves: with or without explanation, no one will ever
dispute this. The oyster, who has neither head nor brain, has, as his
only instrument of action, certain little masses of nervous substance
scattered right and left, which are called _ganglions_. These
communicate with each other and with the organs by nervous cords, which
are interlaced in all directions, without having any common centre,
and which give the impetus to all parts of the animal.
Well, the human oyster presents to us exactly the same nervous
organisation. It has its ganglions and its nerves to itself, which are
put into communication with the brain by some threads strayed among
his own, but which are not under its orders, and which treat with it
on equal terms. You remember, perhaps, the little republic talked about
when we first entered the digestive tube; you have now the explanation
of it. This republic is the original animal; it is the feeding-machine.
I cannot describe it, and the kingdom of which you are queen, better
than by comparing them to two States having diplomatic relations with
each other, who exchange dispatches and reciprocal influences; and as
to the importance of these respective influences, if one were to compare
them I scarcely know to which side the balance could incline.
We shall return elsewhere to this detail, one of the most interesting
of our organisation, and which here finds its natural explanation. For
the present I will content myself with reminding you that, since the
earliest days of human civilisation, all philosophers, all poets, and
all moralists, whether sacred or profane, have borne witness to that
double life within us, that inward being, blind and deaf, whose
disordered impulses so often carry trouble into those higher regions
where will and reason sit enthroned. Behold him taken in his lair at
last, this mysterious being. I have just unveiled his origin to you.
And here, dear child, I must shelter myself behind a profession of
faith. There will not be wanting people to tell you that it is degrading
man far too much to look so low for the sources of his organisation,
and that this sentence--_the human oyster_--which expresses my
idea so well, is neither more nor less than blasphemy. Let them talk,
but adopt their opinion only when they have proved to you that man had
a special Creator, and that the oyster came from a different hand from
ourselves. I should like to know with what face we could venture to
complain, poor worms that we are, because it has seemed good to our
common Father to carry forward in us his previous creations, and in
what respect human dignity would suffer from this contact with a being
who, like us, is one of the works of God. That human pride may suffer
thereby, I admit, and I am glad it should; but if God has included all
creation in His love, we may well include it all in our respect. Whence
comes our superiority at all, but from the gratuitous gifts of Him who
has made us what we are? Is it to lose it, then, to find ourselves
side by side with inferiors whom the Divine benevolence has visited
like ourselves? Surely not. But enough of the oyster, who has never,
that I am aware of, heard such strange discussions sounding in his
ears before. I have no time nor courage now to speak of the other
mollusks, who offer more or less the same system of organs which I
have just described. I must hasten on to the Worms, who give us the
last clue to the great enigma of the animal machine.
LETTER XXXIX.
VERMES--ZOOPHYTA. (_Worms and Zoophytes_).
_Worms._
The worm of worms, the one you know best, is the earthworm: so he shall
have the honor of representing his group.
He will not take much time to describe. He is, in brief, a tube, open
at both ends, so as to allow food to come in and go out. That is all.
I talked to you before about the ruminants, those food-manufacturers
who are employed in cooking victuals for the stomach, and in disengaging
albumen from the coarse materials among which it is apparently lost,
so as to give it out again in a more acceptable form. The ruminant has
other workmen under him, whom I keep in store for you as the last of
the eaters, and who prepare the raw material for him*. These are the
vegetables, who seek out the elements of albumen in earth, water, and
air, those final sources of all alimentation. The earthworm also is
a _preparer_, but in a peculiar way. Look along the garden-walks
in summer-time, after rainy weather: you will see here and there,
little heaps of earth moulded into small sticks, like dough which has
been passed through a tube. [Footnote: M. Mace's account of the
earthworm's life seems founded on the assumption that it extracts its
nourishment from the earth itself, i.e., from inorganic matter, as
_vegetables_ do, to use his own words. But this notion is so
entirely at variance with present received opinions, and also with the
fact that the animal possesses a gizzard for digesting, as well as an
intestinal canal, that it has been necessary to make considerable
alterations in the description. To dismiss his theory of the primitive
animal, etc., altogether, was, however, impossible, without omitting
the whole chapter; but as young heads are not likely to trouble
themselves about it, and it is very innocent in itself, it will do no
harm; subject to this warning, that M. Macé has taken the earthworm
for a more simply organised creature than it really is.--TR.] This is
the damp soil which the worm has passed through his tube, after
extracting from it, during its passage, the various elements of
fertility he requires for the support of his life. This is what makes
him so particularly fond of garden soil, because it is richer in animal
and vegetable matter than common earth, and proves therefore more
nourishing food. The worm, then, feeds on the fat of the earth, which
he converts into azotic aliment for the use of moles, hens and Chinese.
It only figures, it is true, for want of something better, in Chinese
cookery, so profusely hospitable for all that; but the hen doats upon
it, and you do not despise it yourself when it comes back to you in
the form of a chicken's wing, that second transformation of the matter
of which the soil of your garden is composed. It is told of certain
savage tribes, the victims of constant scarcity, that they swallow
little balls of clay in order to keep down their hunger; and during
the great famines in India the distracted inhabitants may, we are told,
be seen digging up the banks of the rivers to feed on the fertile clay
in which the splendid vegetation of their country is developed. This
is a desperate trial of that primeval system of alimentation which
answers perfectly with the worm, but becomes a cruel mockery in the
case of an organisation as exacting as that of man. Let us examine a
little more closely, then, this wonderful tube.
At first sight one notices, to begin with, that it is composed of
perfectly distinct rings, all quite alike. Inside as well as out each
of these rings is an exact repetition of the other. They are all formed
of circular muscles, enclosed between two coats, which extend from one
to the other. A series of ganglions, arranged in the form of a necklace
along the whole length of the body, set in motion the muscular system
of the rings, each of which possesses its local centre of impulsion.
Each feeds itself in its place from the nourishing juices with which
it is in contact, the interior coat enjoying the double property of
distilling digestive juices and absorbing digested ones. These juices
pass through the muscular partition, and proceed to bathe the outer
coat, which plays, at the same time, the part of coat and lung, and
affords a passage to the air through its soft, damp surface, like that
of gills. From all this results a fine red blood, such as we have not
met with since we left the reptiles, and which is manufactured in all
parts of the body at once.
Each of these rings, then, the worm's only organs, is a little eating
machine to and for itself, and at the same time a little movement
machine also; in fact, a complete animal. Each one could, if necessary,
nourish itself and live apart; and this is what he really does. Learn
hence, to despise nothing in nature. One tramples an earthworm under
foot, and there below one's heel lies a little revealer of secrets,
whose organisation throws the most unexpected light upon one of the
greatest mysteries in our own life.
I said to you before, and I felt at the time that it was rather beyond
you, that "each one of our organs is a distinct being, which has its
particular nature and special office, its separate life consequently;
and our individual life is the sum total of all these lesser lives,
independent one of the other, but which nevertheless blend together,
by a mysterious combination, into one common life, which is diffused
everywhere, but can be apprehended nowhere in particular."
The study of the worm admirably explains this out-of-the-way sentence.
And here observe my adjective--my out-of-the-way--for it is a case in
point. We may call it a literary worm; a worm of four rings, each
perfect in itself, but yet compounded together into a whole with its
own idea.
That which makes this idea of life most difficult to comprehend is,
that one cannot prove it by a direct experiment, since there is not
one of our organs which could exist separately from the others. Although
independent in their special action, yet these multiplied lives are
nevertheless in a state of absolute and mutual dependence, from the
imperative need they have of each other to make them act, each having
for its share only one particular function, the effect of which extends
to all the others. This is called the division of labor; and if you
still do not understand me clearly, I will explain it in another way.
The heart sends to all the organs--does it not?--the blood, without
which they could not live: separated from the heart, the lungs would
die immediately. It is to the lungs the blood goes to find the air,
without which it could not maintain life. Separated from the lungs,
the heart would die immediately. There is nothing belonging to us which
can avoid the inexorable requirements of blood and air;
consequently, there is nothing which can live an isolated life.
I will borrow a simile from human society which you will understand
at once. In civilised countries, where division of labor is established,
the tailor makes clothes, the mason makes houses, and the baker makes
bread. If you could throw them each alone by himself into a wood, the
mason would not be able to dress himself, the baker would sleep in the
open air, and the tailor would not know how to make bread. Or rather,
as not one of them can carry on his trade without the co-operation of
a multitude of hands, they could none of them do anything at all. Each
completely independent in his work, yet each dependent upon the others,
both for living, and even for being able to work, our workmen can only
act when they remain bound in close union with the vast society of
which they form a part; and our organs--those other laborers whom you
have seen working for so long--our organs are just in the same
predicament. But in the primitive societies, among savage tribes, where
each man can make his clothes, his house, his bread (when he has any),
and everything else for himself, you might take such an individual if
you liked, and separate him from the rest of the tribe, and he would
go on living as before. And so with the rings of the worm, that
primitive society of organs. Each of them is a universal workman, who
knows how to make everything. Separate him from his fellows, it will
not disturb him at all, and he will go on living as if nothing was
thematter.
I still remember some profound reflections I indulged in one day some
years ago whilst leaning on my spade and looking at a worm that I had
just cut in two, and whose two halves were walking off one on each
side.
"There was only one creature here just now," I said to myself, "and
now there are two! Have I had power, then, to create one with a stroke
of the spade?"
I had not then got hold of the key which I now give you, and to which
no possible objection can be raised. If there are two beings after the
stroke of the spade it is because there were two before. Nay, there
were even many more, if we may trust to the "Manual of Zoology" by
Milne Edwards, a very good book, excellent for an old scholar like
myself, and which I have found very useful in my country-home, as it
has enabled me to relate to you one after another the mysterious wonders
of life.
He says that, "if one cuts an earthworm across into two, three, ten,
or even twenty morsels, each of these morsels will go on living in the
same way as the whole, and will form a new individual."
Twenty! that seems to me a great many, because, as far as I can trust
to my brief observations as a gardener, it is necessary that some of
the rings should remain united together and afford each other mutual
support, in order to succeed in repairing the bleeding breaches; but
I would much rather believe it than try the operation. My mind is easy
when I am defending the plants that I have sown in my garden from the
gluttonous worm who would rob them of their food; but it would not be
so if I were cutting them up on my table to learn something about them.
Besides, there is no need of an operation to convince oneself of the
particular life of each ring. There is one worm, well known by name
at least, though happily not to be met with every day, and that is the
tape-worm, who establishes himself in the intestine of man, and lives
on the chyme, as the other worm does on garden-mould. They call him
the _Solitary_ worm in France; and if ever one might suppose a
creature appropriately named, it would surely be him; for certainly
there is not much society to be looked for in the dwelling he chooses
for himself! But it happens that this pretended _solitary_ worm,
with his unlimited chain of rings, is only a long row of perfectly
distinct beings, so distinct indeed that, from time to time, some of
the rings let themselves go, fall off like ripe fruit, and go away to
live elsewhere, ready to become the nucleus of a new set, if a happy
accident carries them into another intestine, the only place favorable
to their development.
At last, then, here is a corner of the curtain raised; here we see the
associated organs which constitute an animal, living for once a life
positively and in all respects their own. We are now satisfied about
this; and when at another time we find them bound together in the
chains of a union too ingenious to be severed with impunity--which we
shall discover by seeing their action stop at the moment of separation--
we shall know the cause.
Do not think, my dear child, that a wretched earthworm can prove nothing
as regards other creatures. The worm is the starting-point of all the
organisations which come after him. Of what is he composed? Of a
tubewhich is itself composed of rings. Well, it is upon this very tube
that the whole animal machine has been founded: and these rings, as
they expand and modify themselves in a thousand different ways, give
birth to all those varieties of being which drive classifiers to
despair, because they will not understand that there ought only to be
one animal, since there is only one Creator of animals. Now, this
animal is a digestive tube served by organs; it is a worm, _i.e.,_
which goes on constantly embellishing itself. I said to you long ago,
and at a time when you scarcely knew anything, "Have you ever observed
a worm or a leech in motion? You see a successive swelling up of the
whole surface of its body as the creature gradually pushes forward,
as if there was something in its inside rolling along from the tail
to the head. Such is precisely the appearance which the oesophagus
would present to you as the food passes down it, if you had the
opportunity of seeing it in action; and this has been called the
_vermicular_ movement, in consequence of its resemblance to the
movement of a worm."
And afterwards, in speaking of the intestine:
"If your body were made of glass, so that you could look through it
to watch the intestine at work, it would appear to you like an enormous
worm, coiled up into a bundle, heaving and moving with all its rings
at once."
You have now got hold of the secret, namely, that from the beginning
to the end of the digestive tube, its movements are those of a worm.
What a wonder! and that the worm is a digestive tube which can walk.
This worm, or this tube, whichever you please to call it, has never
ceased crawling under our eyes since we began this study. Lost sight
of in man in the midst of the riches he has picked up on his road,
invisible and coiled backward and forward in his palace like an Eastern
despot who leaves everything to be done by his slaves; behold him here
in his first stage naked, shivering in the air, forced to go off himself
and alone to his pasture--ground! But in the coarse earth with which
he fills himself I can already see the delicate chyme which his numerous
servants will prepare for him later on, and into which the heart-tree
will one day send down its roots--the chyliferous vessels.
A short time ago I called the oyster the primitive animal, but I was
in too great a hurry. The worm is the real primitive animal. He is to
be found in the oyster, as the oyster is to be found in us; and that
poor little beast is, by comparison, an animal of high pretension, who
would be shocked, I am sure, if he could understand what we are saying,
and heard us assert that he is nothing but an embellished worm.
_Zoophytes._
Two centuries ago it was believed that below the worm, animal life,
properly so called, ceased, and the creatures whom I am about to
introduce you to were supposed to be animated plants rather than living
organisms. Hence their name was especially chosen to express that
double nature by which they were thought to have a share in two kingdoms
at one time--viz., the animal and vegetable--_zoon_ in Greek
meaning animal, and _phuton_ a plant. Zoophytes were set down as
animal plants.
And although later discoveries have long ago established the fact of
the complete animality of zoophytes, the old name is still in general
use. But you must not let it deceive you. Zoophytes are animals every
inch of them, however low in the organic scale, and although many of
the compound ones imitate the growth of plants and shrubs so exactly
in their mode of spreading that it is only by the closest observation
we can persuade ourselves they do not belong to the vegetable kingdom.
Of these there are the delicate buff-colored, prettily-branched, horny
specimens found on the shore, which make so beautiful a variety in
seaweed pictures among the red and green colors of the real seaweed;
but of these also are those wonderful stony shrubs which grow on the
submerged rocks of islands in warm seas, and the material which you
know so well by the name of coral--the very coral of which the necklaces
and bracelets in the jeweller's window are composed.
In all cases of compound zoophytes, however, there is one great point
which they have in common with the worm, viz., that there is an
association of distinct lives acting unanimously; or, rather, to the
same end. Plainly as this is seen in the worm, it is still more obvious
in the zoophyte. There is no need here either of cutting them up
yourself or of taking other people's dissecting operations upon trust.
It is enough to use your eyes, with the help, it is true, now and then,
of the microscope's clearer sight.
You know the old oak-tree which stands on the outskirts of the wood,
and is called among the country folk _the patriarch_? Now, this
is clearly not an individual, but a nation. It is not a tree; it is
a forest. Nay, may I not call it a green field? For this trunk, so
truly venerable from ages of growth that one feels inclined to bow to
it as one goes by, is, in fact, a collection of structures, accumulated
by countless generations of fleeting herbs, _i.e.,_ leaves, not
one of which has lived for the space of a whole year round. Every
spring some thousands and thousands of buds open to the sun; each one,
therefore, affording a passage to a little green point; and this point
is an oak, who comes into the world, like the first oak, the grandfather
who formerly came forth from an acorn, under the form of an herb or
tender leaf, which a sheep might have browsed upon. Yet it is so
thoroughly an oak, that you have only to take out the bud carefully
before it has expanded and fasten it into another one's place upon a
tree of the same family, though of a different species, and it will
produce an oak of the same sort as its old companions, and which will,
as it progresses, look quite a stranger among the indigenous branches.
This is the secret of what the gardeners call _grafting_, and I
advise you to try the operation upon rose-trees, for nothing is more
amusing. When the autumnal frosts set in, all these troops of new
little oaks die, and deliver up their leaves to the wind; but they
leave behind, as their summer's work, a tiny morsel of new wood, upon
which, if you look carefully, you will see a fresh bud dawning--the
hope of the coming season. And thus the great life of the tree is
perpetuated from century to century by an uninterrupted succession of
transient lives, reminding one in all respects of the life of a nation;
and the similitude is complete in the evergreen trees, where the new
leaf makes its appearance before the old one has quitted the stem.
And such is the life of the great stone trees and shrubs of various
kinds which grow under tropical seas, and whose makers and inhabitants
are the coral polyps, the undoubted heads of the Zoophyte race.
But before considering the _polypidom,_ or external dwelling
(otherwise called the _coeneciun,_ or "common house"), you must
learn something of its originator, the little _polyp,_ who lives
inside, and belongs to a family so widely spread over the face of the
earth, that there are scarcely any waters, whether salt or fresh,
without them.
In your own neighborhood, if you know how to look for them, are to be
found on the banks of ponds, or along the borders of streams which lie
sleeping in roadside ditches, extraordinary beings which, a hundred
years and more ago, completely bewildered the good Dutch naturalist
Trembley, who had taken it into his head to study them. Picture to
yourself some very tiny bags made of a kind of jelly; gray, brown, or,
most commonly of all, green in color, always transparent, and fastened
by their base to the stalks of _carex,_ water-lentils, or the
confervas, which grow in still water. A hunter on the watch, this bag
shoots out on all sides a number of slender threads, like so many
whip-lashes, arranged within a circle round the edge of its opening
or mouth; and with these whip-lashes all the animalcules which come
within reach are entwined, stifled, and carried away to the ever-yawning
little gulf, where they are digested in less than no time. Whatever
will not digest comes out afterwards by the way it went in. Of what
becomes of the results of this digestion it is impossible to form an
idea. Were you to cut up the bag and put little morsels of it under
the best microscope possible, you would see positively nothing but
solid jelly, without the least sign of any organisation whatever. But
this is not all. Replace these morsels in the water, and come back
tolook at them at the end of five, twenty, or thirty hours. Each one of
them will have become a perfect bag, ready to multiply itself afresh
if you submit it to the same operation. Sometimes, on some part of the
original bag, there suddenly appears a little raised spot, like that
which came on your baby brother's arm the other day after he had been
vaccinated. What would you have said, if this ugly spot had grown
larger and larger without stopping; if it had assumed legs, arms, and
a head, and so become another baby, growing from the arm of the first
one? Yet this is just what the spots do which come on the bag I have
been telling you of; and people have come across bags of a larger
species still--between one and two inches in size, in fact--which in
this way carried twelve young ones on their backs, if one is allowed
to talk of stomachs having _backs_. You perceive at once that
this commencement of animal life is not even a digestive tube, and
that nothing in it can he found but a stomach, opening straight to the
air above and closed up below.
It was Réaumur, the originator of the famous thermometer, who gave a
name to the wonderful bags discovered by Trembley. Aristotle had
previously bestowed the title of _polypus_ (many feet) upon a
mollusk outwardly formed upon a similar model [Footnote: This is the
cuttle-fish, called _polypus_ by old naturalists. We shall speak
of it fully hereafter in the history of the movement machine.] with
large whips disposed regularly in a circle round the mouth, and intended
for a similar use, only that they have another function besides; that
of carrying the body along in the capacity of feet by clinging on to
the rocks with their suckers as they go. Réaumur transferred this name
to the newcomers, and called them fresh-water polyps, to the infinite
amusement of Voltaire, who had declared that they were only blades of
grass; a new proof, among many others, that in natural history all the
intellect in the world is not worth a pair of good eyes.
But it was soon found out that, in collecting these bits of living
jelly near the Hague, Trembley had laid his hands on little beings of
immense importance on the surface of the globe, and that he had
discovered under his microscope the explanation of a mystery which had
spread itself, setting human science at defiance, over some thousands
of square miles.
I talked to you just now of the jeweller's coral, of which ornaments
so becoming to dark-haired people are made. That is one of the stony
polypidoms I spoke of as stone trees found at the bottom of the sea,
where it grows attached to the rocks in the form of a charming little
shrub, stretching its red branches in all directions. The Greeks, who
were never at a loss, relate that Perseus one day laid down upon the
sea-shore the famous head of Medusa, the sight of which had the property
of turning everything to stone, and that the nymphs, in sport, showed
it to the coral shrubs; a fact which explained everything quite
naturally. Without exactly holding this mythological explanation,
modern philosophers had not got much farther, and coral was still a
puzzle to them, which they were not fond of troubling themselves about;
till, roused by Trembley's revelations, they examined it more carefully,
and discovered in its soft extremities (hitherto unnoticed) those same
living jelly-bags or sacs, with their circlets of legs, or rather arms,
charged with supplying them with food. These were marine polyps, which
grow, like those in fresh water, one upon another, but each in its own
crusty cell; and like the buds of the oak, these buds of the stony
tree form each its special deposit, which it bequeaths in dying to the
general mass. In short, as the tender shoot of the oak is filled by
degrees with the wood which forms within it, and hardens into a branch,
that goes on increasing by perpetually new growths, so the jelly polyp
of the polypidom hardens below into stone and dies incessantly at the
base, while it lives on indefinitely above in its constantly-renewed
summit.
Do not get tired of all this phantasmagoria, my dear pupil: it is a
matter of the highest interest. Here is the point of junction--the
bond, as it were, between the three kingdoms: an animal growing
vegetable-wise produces a mineral mass, extracted from the waters of
the sea by an infinity of little living crucibles, who carry on under
our eyes the work begun in the first ages of the globe, and quietly
manufacture continents for the use of future generations. This ought
to console you, my dear child, for being little. It is by little things
that God loves to effect what is truly great. He did not seek out the
elephant or the whale to form these worlds; He chose workmen no bigger
than a pin's head. I have spoken to you about jeweller's coral, which
is made into toys or presents for ladies to adorn themselves with; but
its brethren, the madrepores of the Pacific Ocean play a very different
part. They have formed in front of the shores of New Holland a barrier
of reefs three hundred leagues in extent and twenty wide. What are all
our buildings after this?--those pyramids and cathedrals which seem
so gigantic to us? This ever-increasing wave of coral polypidoms will
one day shut against navigators the entrance to one part of the sea's
tropical region; and lands not to be found on the map to-day will then
lie stretched out under the sun, covered with plants and animals; and
this in places where ships now plough the ocean. Know, also, that a
great portion of the soil which we tread under foot has no other origin.
It was manufactured formerly in the sea by infinite myriads of beings,
often infinitely small. Each one, whether polype or shell, produced
its grain of stone, and from all these grains God, who directed their
work, has made our country.
But it is time to bring this chattering to a close, for it will never
end if I do not force myself to stop. I leave it with regret; but all
these paths through which I have threaded my way one after another
without counting them, have already made a volume which may possibly
be considered too large for you. There are many other zoophytes besides
the coral polypes, and all of them beautiful and curious. They all
inhabit the fertile depths of the waters where God has deposited the
first germs of life. I cannot describe them to you now. But to make
amends, I will give you a piece of advice which will perhaps make some
people stare. Ask your papa to lend you Michelet's book, _The Sea_,
and look there for what is said about the mysterious animals which lie
hid beneath the waves. His book was not written for you as this one
is: and if, in spite of all my good intentions, I have not always
succeeded in being as comprehensible as I meant to be, Michelet, who
never thought about little people when he took up his pen, will
certainly startle you now and then. But do not be disheartened by a
word. You will find there, that which will be forever plain to you,
the poesy of nature, and children comprehend that better than learned
men.
LETTER XL.
THE NOURISHMENT OF PLANTS.
One more word before we part about the last of the eaters, about
Vegetables. They will furnish you with a new and very clearly marked
proof of the uniformity of the fundamental conditions to which the
Author of life has subjected all organised beings.
Let us look once more at this oak, of whose manner of growth I was
obliged to give you a sketch beforehand, in order to show you the ties
which unite it with its immediate neighbors in the animal kingdom. How
does it feed? I need not tell you this. It feeds by its roots, which
suck up in the bosom of the earth the water charged with the juices
which form its nourishment. Are you aware that every large branch had
its subterranean fellow or representative, and that the annual shoot
at the top of the tree is reproduced at the base by fresh fibres, which
extend themselves in the soil of the earth, in proportion as their
sisters above make their way in the air? And thus, by means of organs
ever young, the life and progress of the great association is kept up,
while those members whose day of work is over still remain there as
the supports of the edifice. It is the same with human societies. They
are sustained by what is old, but they live and progress only by what
is young. The sap, then, which is the name given to the moisture or
water sucked in by the young roots, having once got into the cells of
which the tissue of the fibres is composed, passes from one to another,
and travels thus to the top of the tree, where it is wanted by the
leaves.
There is no obvious machinery here, however, to impel it forward. It
journeys on of itself, as it were, under the action of laws which have
never been satisfactorily explained, but all of which are dependent
on the vital force or life-power of the tree, inasmuch as without it
there is no circulation. One agent, but by no means the principal, or
it would act as well in a dead tree as a living one, is _capillary
attraction_; and, if you wish to know what that is, you have only
to think of what happens to a towel, if you hang it upon a peg, and
leave the end of it soaking in water. Does not the "wet" seem to climb
up it thread by thread, till it is damp from one end to the other? A
little in this way--but these similes are very imperfect, and will not
bear close application--the sap rises in a tree, stealing up branch
by branch; and it is then called _ascending sap_. [Footnote: M. Macé
speaks of this sap as the _blood of the tree_, and of the leaves only as
_lungs_. These statements have been modified so as to meet the fact that
_ascending sap_ consists of, and conveys the raw elements of _food_ to,
the leaves; that in the leaves this food is _digested_, as well as
brought in contact with the air, and that it is thus converted into that
nourishing fluid, the _descending sap_, which certainly plays the part
of steward to the tree as our blood does to us, and therefore may now be
called the blood of the tree. It must be remembered, however, that each
tree has its own sort of steward, as the case of the _Euphorbia_ (quoted
afterwards) plainly shows. The analogy with the more general substance
of blood is therefore not very complete.-TR.]
It arrives at last at the leaves, which it enters as our food enters
our stomachs, and for the same purpose; for in them takes place, as
in all true stomachs, that process of digestion by which the elements
of the crude sap-food are decomposed from their first condition, and
converted into a nourishing chyle; in each tree of a sort "after its
kind."
But more than this. Like the outer coat of the earthworm, the coat of
the leaf affords a passage to air and moisture through its surface;
and here, therefore, takes place that mysterious exchange which is
everywhere the essential condition of life. Here is the charcoal-market
as before, only the bargainers have changed parts. The air, which in
the other case received the _carbon,_ delivers it up, now, and
receives oxygen in exchange; exactly the reverse of its traffic with
animals. In other words, the tree inhales through its leaves the
carbonic acid gas thrown into the atmosphere by our lungs. On its own
responsibility it breaks through the alliance between the carbon and
oxygen contracted in our organs; keeps the carbon for its own use, to
restore it to us another day under the form of wood, or, by the aid
of the charcoal-burner, in the pure and simple state of charcoal; and
sets at liberty the oxygen, which once more goes off in search of new
lungs and a fresh alliance. Thus a constant equilibrium is maintained
in the atmosphere; and thus, by a system of perpetual rotation or
everlasting merry-go-round, the same substances serve, indefinitely,
to support life of every opposite description.
Now there are two things to be remembered in this inverted respiration
of vegetables. In the first place, it occurs only in the parts which
are _green_. Flowers, fruit, the root, and every part of any other
color, do as we do when we breathe; _i.e._ deprive the air of its
oxygen, charging it with carbonic acid instead. For which reason,
by-the-by, we ought not to keep flowers in a bedroom at night. Charming
as they are, they are _poisoners_, and a headache is what we may
fairly expect after sleeping shut in with them in the same room. It
is almost as bad to allow green boughs to remain there either, for,
in the dark, even the green parts cease to purify the air, and begin
like the others to manufacture carbonic acid, at the expense of course
of their carbon, which thus by degrees is used up. Now, as it is the
carbon which constitutes the solid fibres of plants and produces their
green color, they soon become yellow and limp when deprived of light.
You may, perhaps, have wondered why the gardener amused himself with
smothering his poor lettuces by tying them up at top like a knot of
"back hair," instead of letting them grow freely in the air and
sunshine. It is, my dear, to make them more tender and delicate for
you to eat; and those beautiful, crisp, yellow leaves, so delicious
to the tooth, would have been green and tough, had they not slowly and
quietly let out a great portion of their store of carbon in darkness
during the last few days, before being gathered. Even without playing
the gardener, you may assure yourself of this fact in a still more
simple manner. Put a flat board upon the lawn and leave it there for
three days; then take it up again, and you will find just where the
board has prevented the light from reaching the grass, a yellow mark
so distinctly traced as to be seen from the other end of the garden.
But to return to the sap, which we left undergoing a change from air
and solar influences in the leaves. The ascending sap was to all
appearance only clear water. When it returns from the leaves, charged
with carbon, it is a thick juice having almost the consistency, and
sometimes even the color of milk, and is possessed of properties
altogether new. The most striking example that I can give you of
thedifference of the two states of sap is the Euphorbia of the Canary
Islands, whose digestive or descending sap is a violent poison. When
the natives of the country are accidentally pressed by thirst, they
carefully remove the bark in which the fatal juice circulates, and are
then able to refresh themselves safely by sucking the stem, which
yields only the watery sap sucked from the ground, and as yet unaltered
and harmless.
Each of these two saps, in fact, has its path distinctly traced for
it: the first rises through the wood, the second descends through the
bark, whence it is called descending sap. If you wish to satisfy
yourself of this, fasten a rather tight knot of pack-thread round a
young branch, and after a time you will see it pine below the knot and
become swollen above it, an unanswerable proof that the nutritive
juices flowed downward through the bark; for the wood inside the branch
will have been uninjured by the strangling pressure. Remember this,
my dear, when you are playing in the garden, and do not injure the
bark of the young trees your father likes so much to see flourishing.
It is by the bark that they are nourished, and you might even kill
them by treating it too roughly.
And now I must show you how the nutrition is carried on, or, if you
like better, how the tree grows by means of this descending sap. See:
here is a fir tree, which has just been cut down to the ground. Now,
if you like, I will tell you in a moment how old it is. I will even
tell you the age of every branch, little and big ones both, without
making a mistake in a single year; and you know as well as I do that
I am no conjuror. You see these small circles so delicately drawn, as
it were, upon the face of the sawn trunk, each wider than the last,
as if they were composed of a set of tubes, of unequal sizes, fitting
exactly into each other. Now count them; and you will perhaps find
twenty-five; and as each of these circles represents the work of one
year, you will know that the tree is twenty-five years old. In spring,
when the sap begins to move more briskly, it deposits everywhere between
the wood and the bark, from the trunk to the farthest boughs of the
tree, a uniform layer of a thick liquid, which moulds itself exactly
upon the wood already formed. This layer stiffens during the year; it
gets filled with the carbon left in it atom after atom, by each drop
of the descending sap as it goes by, and thus insensibly becoming
organised and hardened. When winter arrives to interrupt the work, it
will have formed two _ligneous, i.e._ woody layers, as they are
called. Of these, one belongs to the wood, and will never move again
so long as the tree lasts, for it will be covered over, and as it were
buried, by the successive layers yet to come; while, on the contrary,
the other (layer) belongs to the bark, and is doomed to find itself
perpetually forced outwards by the fresh layers, which will after a
while insinuate themselves between it and the wood.
It is for this reason that the bark of old trunks of trees is so deeply
furrowed, and that the dry scales may be picked off the surface without
the slightest injury to the tree. It is part of the original bark,
dead long ago. The old wood also is dead inside, and even when it is
altogether gone, the glad youthful branches growing green in the
sunshine will scarcely find it out! This accounts for those oaks which
time has hollowed without destroying, as those of Allonville in
Normandy, in which mass is said, and which is moreover the greenest
tree in the country. But without going so far, who has not seen those
hollow old willows, sometimes pierced with holes letting in daylight,
yet proudly crowned above by a forest of young boughs, as green and
full of vigor as if the trunk were still in its prime? What was dead
has departed, but all that has life in it remains, and that is enough
for the tree.
Need I add that the descending sap, this steward of the vegetable, has
also his workmen to supply with materials, as in our case, and that
he is always falling in on his road with organs, all of which want
different things from him? That here a flower has to be formed, there
a fruit, there a leaf, or a bit of wood, and so on: and that a
mysterious intelligence--the same that we have found everywhere
else--presides over all these varied constructions, the materials for
which are mixed together pell-mell, in the imperceptible thread of sap
which oozes from the leaf to the bark? I recollect just as I am about
to conclude, my dear child, that I once told you, you were a small
temple in which God perpetually attests His presence, by a permanent
miracle. You may now henceforth look upon a tree as something more
than a bit of wood, yielding a pleasant shade. God is in it also.
CONCLUSION.
And now, my dear little pupil, to what conclusion do we come from all
this? To that which I announced to you from the first. Throughout the
length and breadth of creation, from the highest to the lowest grade,
every living thing is subject to the same law. Everything eats, and
eats nearly in the same manner, since everywhere the same substances
furnish the feast. I laid down in my first letter that our feeding
machine was reproduced even to the farthest limits of the animal
kingdom, though always becoming more simple as the species descends
in the scale. And afterwards, where we began the study of animals, I
told you that in this machine lay the uniformity of their construction.
Was I not right? and what could I add to all the proofs which have
developed themselves one after another, to establish the fact of this
uniformity of plan in the animal machine, in all its essential points?
And it will be to the lasting renown of the illustrious Geoffroy St.
Hilaire that it was, in the face of all the Academies and under the
fire of very learned indignation, he proclaimed this truth, which one
cannot lose sight of without losing one's way in a crowd of arbitrary
fancies.
I return, then, to the definition which I gave you in speaking of the
worm, and which is the final word of the ideas I have been endeavoring
to make you understand. _An animal is a digestive tube served by
organs._
In the first place it must eat, and for this therefore the Creator
provided first. All the rest came afterwards in order to enable it to
eat more readily, to secure its prey more easily, and to make the most
of it when eaten. The movement machine, therefore, whose history I
have promised you, is only an assistant, and not the principal feature
of the organisation, and it is not by it, therefore, that the question
can be decided, whether God has made three, four, or five animals, or
whether he has only made one.
And now, my dear little pupil, I will bid you adieu, or rather say as
the French do, "Au revoir," which means "Good-bye till we meet again,"
begging you to excuse any awkward expressions that may have escaped
me, as also my having now and then talked about things because they
have interested me, without perhaps sufficiently considering whether
they might have an equal interest for you. Yet, while the pen is still
in my hand, I will not leave you my concluding definition of an animal
without adding a word of explanation. You know nothing about such
matters yourself, but to some people my words might have the air of
a parody upon another definition, applied by those grave gentlemen the
Philosophers to man, whom they have denominated _An intelligence
served by organs_. My definition is applicable only to the animal,
and not to man, observe. Man in the natural, physical machinery of his
body, is very decidedly an animal; yet as certainly is he, by the
divine reflection which shines within him, something much more and
greater; but _what_, is so far beyond the reach of definitionthat I
shall not attempt to give you one. "Man," as Jesus Christ has
said, "lives not by bread alone, but by every word that proccedeth out
of the mouth of God." What it is that is nourished in us by that word,
is precisely what I cannot attempt to define for you; yet I think you
have understood my meaning.
Go, then, and eat your food in peace, like the pretty little animal
that you are; but do not forget to nourish also the other part of your
being; that indeed which is of the most importance, and which enables
you to ascend to your Creator.
THE END.
POSTSCRIPT.
In going through the preceding pages (Part II) with a comparative
anatomist, it became evident that some few popular and other errors
and misconceptions had crept into this portion of M. Macé's usually
clear and accurate work.
Naturally it was not in his power to verify all the statements he had
to make on so many and such varied subjects, and he appears occasionally
to have trusted to works of old-fashioned or doubtful authority.
In these cases I have considered it desirable to make such corrections
as should secure the trustworthiness of the descriptions as far as
they pretend to go.
It would not, however, have been in my power to accomplish this, but
for the kind and efficient aid I have received from a scientific student
of these subjects; and I am glad of this opportunity of acknowledging
how much I am indebted to him for his assistance in making the necessary
alterations, as well as for confirming the correctness of the greater
portion of the work.
MARGARET GATTY.
January, 1865. January, 1865.
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