To-day we have to begin by making acquaintance with a new term. I would
willingly have spared you this, if I could, for the word is neither
a pretty, nor a well-chosen one, but we cannot get on without it.
You are aware now that the learned, unknown sponsors, who gave names
to the different parts of the body, bestowed the odd-enough one of
_chyme_ on that pasty substance which passes out of the stomach when the
cooking is over. We have said quite enough about it, and you know enough
of it I am sure. Well! the people seem to have had quite a fancy for the
word _chyme_, for they adopted it again, with only a very slight
alteration, when they wanted to specify separately the quintessence of
the _chyme_ (the useful part that is), which has to unite with the
blood, and which we have been speaking of as the _gold_ of the
aliments--this then they called _chyle_. I give you the name as I
received it, but have no responsibility in the matter.
In concluding the last chapter I said we were sure to find there was
a plan for extracting the best part of the _chyme_, viz. the _chyle_,
from the intestinal canal; and a very simple one it is. A complete
regiment of those little scavengers lately described, are drawn up in
battle-array along the whole length of the small intestine, but
especially round about the _duodenum._ There, a thousand minute pipes
pierce in all directions through the coat of the intestine, and suck,
like so many constantly open mouths, the drops of _chyle_ as fast as
they are formed. They are called _chyliferous vessels_ or chyle-bearers,
just as we might call hot-air stoves _caloriferous_ or heat-bearers--from
the Latin word _fero,_ which means to carry or bear. I mentioned
before that there were, within the intestine, certain elastic valves
which obstruct the progress of the _chyme,_ and oblige it to be
constantly stopping. There are in fact so many of these, and the skin
which lines the intestinal canal is so folded and plaited, that if it
were stretched out at full length on a big table, it would cover at
least as large a surface as that other skin, with which you are so well
acquainted, which entirely clothes the body outside.
Now, the _chyliferous vessels_ we have been speaking of insinuate
themselves into all the plaits and folds alluded to, and thus they
reach at last the very centre of the _chymous_ paste, and not a single
drop of _chyle_ can escape them. They do their work so well, that the
separation is effected long before the paste reaches the large
intestine; and when that has forced its way through the door which
guards the entrance, and which prevents its ever returning again, the
_chyle_ is already far off on its mission. It has threaded its way along
the little pipes, and, always creeping nearer and nearer, is on the
high-road to the heart, where it is anxiously expected.
And what becomes of the rest? There is nothing further to be said about
it, but that it shares the fate of everything else which, having
answered its purpose in its place, is no longer wanted and must be got
rid of. Thus in works where iron-stone smelting is carried on, the
refuse that remains after the ore is extracted, though available for
road-making or other purposes, is thrown out of the manufactory as a
useless incumbrance there.
Our history requires us to follow the fate of that golden aliment the
_chyle,_ which is now in a condition to support the life of the body,
and every drop of which will turn into blood--the blood which beats at
our hearts, nourishes our limbs, and sets at work the fibres of our
brain.
I ought to tell you first that the _chyle,_ when it leaves the
intestine, is very like milk. It is a white, rather fatty juice, having
the appearance, when you look closely at it, of a kind of _whey,_
in which a crowd of globules, or little balls if you prefer it,
infinitesimally small, are swimming about. Some people, whose curiosity
nothing can check, have put the tips of their tongue to it; so I am
able to tell you, if you care for the information, that it has rather
a saltish taste.
At this point it is what may be called new-born blood, and to carry
on the metaphor, blood whose education has yet to be completed. All
the elements of blood are there already, but in confusion and
intermingled, so that they cannot yet be recognised. A wonderful fact,
and one of which I have no explanation to offer you, because among the
many mysteries which are silently going on within us is this, that the
education of the new-born blood begins entirely of itself in the vessels
which are carrying it along. During their very journey, the confused
elements are setting themselves in order and forming into groups. In
short the _chyle,_ when it comes out of the chyliferous vessels,
is already much more like blood than when it entered them, and yet one
cannot account for the change. It is changed, however; its whiteness
has already assumed a rosy tinge, and if it is exposed to the air it
may be seen turning slightly red, as if to give notice to the observer
of what it is about to become.
You know that all our scavengers uniting together deposit their
sweepings in one large canal, which is called the _thoracic duct._
The _chyle_ scavengers arrive there just like the rest, and there
our poor friend finds himself confounded for a moment with all the
dross of the body, as sometimes happens to men who devote themselves
to the public good. But the crisis passes in an instant. A little
further off, the _thoracic duct_ pours its whole contents together
into a large vein situated close to the heart, and the blood has no
difficulty in recognising and appropriating what belongs to him.
Here, my dear little scholar, we conclude the first part of our story.
To eat is to nourish oneself; that is, to furnish all parts of the
body with the substances necessary to them for the proper performance
of their functions. The mouth receives these substances in their crude
condition, the intestinal canal prepares them for use, and the blood
distributes them.
After the history of the _preparation,_ comes naturally that of the
_distribution._
The first is called the DIGESTION. It is the history of the _chyle,_
which begins between the thumb and forefinger while as yet invisible,
hid in the thousand prisons of our different sorts of food, and ends in
the _thoracic duct_, when, disengaged from all previous bonds, purified
and refined by the ordeals of its intestinal life, it leaps into the
blood, carrying with it a renewal of life and power.
The second history is that of the CIRCULATION. It is the history of
the _Blood,_ that indefatigable traveler, who is constantly
_circulating_ or describing a circle (the Latins called it _circulus_)
through the body; by which I mean that it is continually retracing its
steps, coming out of the heart to return to it, re-entering it only to
leave it again, and so on without intermission, until the hour of death.
The history of the _Digestion_, which we have just gone through,
goes on quietly from one end to the other without any complication.
That of the _Circulation_, which we are about to begin, is mixed
up with another history, from which it cannot be kept separate while
the description is going on, although the two histories are in reality
quite distinct from each other. The blood describes two circles, to
speak correctly: 1st. A wide one, which extends from the extremities
of the body to the heart, and back again from the heart to the
extremities. 2d. A more contracted one, which goes from the heart to
the lungs, and back from the lungs to the heart. Whilst circulating
in the lungs, it encounters the air we breathe; and here takes place,
between it and the air, one of the most curious transactions imaginable,
without which the blood would not be able to nourish the body even for
five minutes. This is called RESPIRATION, or the act of breathing.
Digestion, circulation, respiration, the three histories together form
but one--that of NUTRITION, or the act of nourishing; in other words,
of supporting life. This is what I called _eating_ at first, that
I might not mystify you at the beginning with hard words. But now that
we are growing learned ourselves, we must accustom ourselves to the
terms in use among learned people, especially when they are not more
formidable than those I have just taught you.
Our next subject for consideration, then, Will be the circulation; and
we will begin with the heart, since that is to the circulation what
the stomach is to the digestion--viz., master of the establishment.
He is a very important person, this heart, as I hardly need tell you.
Even ignorant people speak respectfully of him, and I am sure beforehand
that his history will interest you very much.
Do you feel as I do, my dear child? I am quite happy at having brought
you thus far on our journey, and at being able to take a rest with you
at the gateway of the new country into which we are about to enter,
like travelers sitting down upon a boundary frontier. What a distance
we have come, since the day when I took you by the hand to conduct you
inside this little body, of which you were making use without knowing
anything about it! How many things we have learned already, and how
many more remain to be learned, of which you have at present no idea!
I assure you I should be almost afraid myself of what is before us
yet, if I did not rely upon my own strong desire to instruct you, and
the tender affection I bear to you. Believe me, the greatest of
constraining powers is love; and when I get bewildered in the midst
of some difficult explanation which will not come out clearly, I have
only to place before me those laughing eyes of yours, where sleeps a
soul that must soon awaken to consciousness, in order to make the
daylight come into my own!
Must I add, too, that I am not working for you only? We are all placed
in this world to help each other, and in striving to bring down light
into your intellect, and good sentiments into your heart, I am thinking
also of those to whom you, in your turn, may render the same good
service hereafter, provided I have the happiness of succeeding now
with you. This ought to be so, ought it not? You should resolve to be
numbered one day among those who have not lived altogether for
themselves, but who have given the world something worth having as
they passed through it. To-day's labor will have been well employed
if, later on, it turns out that this history of the _chyle_ has
not been told you in vain!