If you have thoroughly understood the story I last told you, my child,
it will have revealed to you the whole mystery of the _circulation
of the blood,_ and you are at the present moment wiser than all the
learned men of antiquity and the middle ages, for they had none of
them the faintest surmise of the truth.
It may, perhaps, seem odd to you that men should have existed for
upwards of five thousand years without making inquiry into a matter
which so closely concerned them, and which was so easy to find out.
Is it not almost incredible that so many hearts should have beaten for
so long a period without any of their owners having felt a wish to
know exactly _why?_ Yet so it is. The action of the heart and the
flow of the blood have not been understood for much more than two
hundred years, and the man whose name is attached to this great
discovery richly deserves that we should say a few words about him.
He was called Harvey. He was an Englishman; physician to King Charles
I., who was beheaded in 1648; and when he first ventured publicly to
teach that the blood was constantly circulating from one end of the
human body to the other, perpetually returning and retracing its steps,
a great scandal was created in the world. He was called a fool,--an
impertinent innovator,--a madman. His words shattered old doctrines,
and he only received for his reward all the petty annoyances which men
are apt to lavish so freely upon any one who tells them something new;
because--do you see?--it is so disagreeable to be disturbed in one's
habits and preconceived ideas.
Harvey is not the only one in the history of mankind who has committed
the sin of being right in defiance of the opinions of his age. It is
true posterity takes account afterwards of the labors of genius, and
inscribes a fresh name upon her list. But one must pay for this glory
in one's lifetime. One cannot have everything at once.
This is an old story, my child, but always new nevertheless; and for
my own part it is, I own, one of my pleasures to amuse myself by
reflecting how much cause for laughter three-fourths of the great men
of the present day are providing for the little girls who shall be
alive two centuries hence. Time is a great avenger, and puts many
things and men in their proper places.
Let us pause here a moment while we are speaking of Harvey. I should
be curious to know what any one of the courtiers of Charles I., bedecked
in feathers, ribbons and laces, would have said to the valet who would
have placed the excellent Harvey, with his insane invention, above his
most gracious majesty, the lord and king of all Great Britain! And yet
what is his most gracious majesty to you to-day? What do you owe to
him? in what does he interest you? While you can never hear the name
of Harvey pronounced without remembering that you are under many
obligations to him! A thousand years hence, when society shall have
made the great progress which may reasonably be expected, the name of
Harvey will be familiar to every one who owns a heart, while that of
Charles I. will be only a vanished shadow; a souvenir lost in the maze
of history.
Our debt of remembrance paid, let us return to the heart--the little
closed bag which labors so prettily. We must now inquire the real names
of whatever has figured in our story.
The two great compartments are called _ventricles,_ the two small
pouches _auricles,_ and they are also distinguished as being on the
right or left side;--_right ventricle, left ventricle, right auricle,
left auricle._
The inner doors on which depends all the action of the machine, are
called _valvelets._ By-and-bye, when the pump and the steam-engine
are explained to you, you will meet again with these treacherous doors,
which never allow what has once entered to go back again; but then we
shall call them _valves._
The air-reservoir, I need scarcely tell you, is the _lung,_ to
which the blood goes to put itself in contact with the air.
The subterranean watercourse, of which I hope we have talked long
enough, is _the small intestine,_ in which the _chyle_ collects; and
the tubes which run into it are, of course, the _chyliferous vessels,_
the only channels by which anything reaches the heart which has not
previously gone out from it.
The tubes of distribution, which run out from the machine in all
directions, are called with us _arteries_; the return tubes, which
bring back the water to the machine, are called _veins._
Finally, we have not exactly the _filters_ employed to clear the
water from the impurities contracted as it goes along, for no such
thing exists in us. There are in our case the refuse-chambers of which
I have already spoken, in connexion with the liver, where the blood
disembarrasses itself of any useless materials, and from which it comes
out with clean pockets, so to speak, reverting to the comparison of
which we have already availed ourselves.
As you see, then, everything comes round again; and the bright idea
which our professors hit upon in order to satisfy the caprice of the
banker is exactly carried out in your own body, only a thousand times
more perfectly than could have been done by them all, even with all
their science added to all his money.
I mentioned that the shrewdest of the party boasted about making an
artificial heart. But, let me tell you, there is one thing I would
have defied him to imitate, by any expedient he could devise, and that
is the inimitable construction of the _arteries_ and _veins,_ and the
incomprehensible delicacy of their innumerable ramifications.
Let us talk a little about these marvellous tubes, and begin with the
arteries, which have the most important part to play.
Did you ever see a doctor try the pulse of his patient? Take hold of
your own wrist and search a little above the thumb. You will soon find
the place and feel something beating against your finger. There is an
artery which passes there, and the little beating you feel is the
rebound of the pulsations, of your heart. Every time that the left
_ventricle,_ by contracting itself, chases the blood into the arteries,
these, of which the tissue is very elastic, become distended all at
once, and then contract again, repeating the process whenever a fresh
gush of blood arrives, so that their movement is exactly regulated by
the movement of the heart. It is true the two movements are in a
contrary direction; that is to say, the artery becomes distended, while
the heart contracts, and contracts when the heart enlarges itself; but
that makes no difference to the doctor. What he wants to know is, with
what force and rapidity the heart of the patient beats, and I will
explain why. It is an interesting point in the history of circulation.
When you were very little--very little indeed, my dear child--your
heart beat from 130 to 140 times in a minute. Afterwards the beats
sank to 100 per minute; then to fewer still. At present I cannot tell
you the precise number: perhaps, about ninety. When you are a grown-up
young lady, it will beat about eighty times in the minute; when you
are a mother, about seventy-three times; when a grandmother (if such
a blessing be granted you), only from fifty to sixty times, perhaps
even fewer. People tell of an old man of eighty-four whose heart beat
only twenty-nine times in the sixty seconds.
Observe that in all my calculations I have taken special care to prefix
the word _about_ to the numbers mentioned. And this because, in
point of fact, the heart is a capricious creature, which has no exact
rules to go by. It changes its pace on every occasion--fear, joy, every
emotion which agitates the soul, quickens or retards its movements;
and derangements of health may be detected by its pulsations, which
are infinitely varied in character. In fever, for instance, which is
nothing but a race of the blood at full speed, the hearts of grown-up
people beat as quickly as those of little children; sometimes, indeed,
more quickly still. In certain maladies it goes with great sudden
leaps, like a galloping horse; in others it trots in little jerks;
while in some cases it moves slowly and wearily, and its throbs are
so weak that one can scarcely feel them.
These pulsations, then, afford important revelations to the doctor.
The heart is for him a gossiping confidant, who lets out the secrets
of illnesses, however closely they may fancy themselves hidden in the
remote depths of the body. When the doctor lays his finger on the
patient's pulse, it is precisely the same thing to him as if he had
laid it on his heart, only with this difference, that the one is much
less difficult to do, and much sooner done than the other.
The artery of the wrist is in fact a small heart, not only because it
follows all the movements of the large one, but because it carries
forward the work which the other begins, and assists also in propelling
the blood to the furthest extremities of the limbs, driving it on in
its turn at each of its own contractions. Imagine a fire-engine, whose
pipes should take up and drive forwards along their whole length the
water which is thrown upon the fire, and you will have some idea of
the marvellous machine which is at work in our behalf within us. Nor
are you to suppose that the wrist-artery is a specially privileged
one, because it has been chosen to hold intercourse with physicians.
All the others are equally serviceable; and if they cannot all be
used for "feeling the pulse," it is because they are generally more
deeply buried in the flesh, where it is not easy to reach them.
Observe your mother when she is packing a trunk, and you will see that
whatever she is most afraid maybe spoiled, she is most careful to put
in the middle, so that it may be least exposed to accidents. And this
is what a kind Providence has done with the arteries, which have the
utmost cause to dread accidents; whilst the veins, which are much
better able to bear rough usage, are allowed to wander about freely
just under the skin. But when the bones happen to take up a great deal
of room, and come near the skin themselves, as is the case in the
wrist, the artery is forced, whether he likes it or not, to venture
to the surface, and then we are able to put our fingers upon him.
And there are others in the same sort of situation; the artery of the
foot for instance. But only just think how far from agreeable it would
be to have to take off your shoe and present your foot to the doctor!
The artery which passes to the temple, just by the ear, is another
affair. That would answer the purpose very well in fact, and I even
advise you to make use of it when you want to feel your own pulse. It
is more easily found than the other even, and its pulsations are still
more easily perceptible. Nevertheless, when all is said and done, it
is better for the doctor to take his patient by the hand than by the
head. Merely as a matter of good manners.
I will now make you acquainted with the principal arteries, and the
manner in which they distribute the blood through the body.
The whole of the blood driven out by the left ventricle at each of its
contractions, passes into one large canal called the _aorta_. The
_aorta_ as it goes away at first ascends; then bends back in a curve;
and from this curve, which is called the _arch of the aorta_ (from its
shape) diverge right and left, certain branch-pipes which carry the
blood into the two arms and on each side of the head; and which are, in
fact, the beginning, or upper end, of those whose pulsations we feel
with our fingers in the two wrists and at the temples.
The supply to the upper part of the body being secured, the _aorta_
begins to descend. But now imagine of what importance it must be, that
this head-artery--the foster-father of the whole body--should be
sheltered from every accident. The _aorta_ once divided, death is
inevitable; you might as well have your head cut off at once; and
thus it has been fixed in the best--that is to say, the safest--place.
Of course you know what is meant by the _backbone_ or _spine_, called
also the _vertebral column_, in consequence of its being made like a
sort of column composed of a series of small bones fastened together,
which are named _vertebræ_. Touch it and feel how solid it is, and how
few dangers there can be for anything placed behind it. Well, that is
the rampart which has been given to the _Aorta_. As this descends, it
slips behind the heart and takes up its place in front of the _vertebral
column_ which it follows all the way down the back, just to the top of
the loins. There it is, so to speak, almost unassailable; in fact hardly
any cases are known of the _Aorta_ being wounded; to get at it, it would
be necessary to bestow one of those blows which used to be given in the
time of the Crusades, which cut the body in two. There was an end of the
_Aorta_, as of every thing else then; it was unfortunately not worth
talking about any longer!
The next time you see a fish on the table, ask to be shown the large
central bone. It is the fish's _vertebral column_, and it will give you
an idea of your own, for it is constructed on the same plan. You will
perceive a blackish thread running all along it--that is _the aorta_.
As it descends, the _aorta_ sends off on its passage a great number of
arteries which carry the blood into all parts of the body. Arrived at
the loins it forms a fork; dividing into two great branches, which
continue their descent, one on each side the body, down to the very
extremities of the two feet.
As you perceive, dear child, this is not very difficult to remember.
A large fork, whose two points are at the tips of the feet, the handle
of which curves at the top like the crook of a crozier; from this curve
come four branches, which pass into the two arms and to the two sides
of the head--and this is the whole story. But of course, it would be
another affair were I to enter into the detail of all the ramifications.
Here it is that all engineers, past, present, and future, are baffled,
defeated and outdone! Choose any place you please upon your body, and
run the finest needle you can find into it what will issue from the
puncture?
"Thanks for the proposal," you say; "I have no occasion to try the
experiment, to discover that blood will come out."
You say that very readily, young lady; but have you ever asked yourself,
what is implied by your being so sure before hand that you can bring
blood from any part of your body if you choose to prick it, though
never so slightly? It implies that there is not on your whole frame
a spot the size of a needle's point, which has not its own little canal
filled with blood; for if there were such a one, there at any rate the
needle would pass in without tearing the canal, and causing the blood
to flow out. And now count the number of places from the top to the
bottom of your dear little self, on which one could put the point of
a needle, and even when you have counted them all, do not fancy you
have arrived at the number of the tiny tubes of blood. Compared to
these, your needle is a coarse stake, and tears not one but a thousand
of these little tubes in its passage.
That seems to you rather a strong expression, does it not? But let me
make good my boldness. A needle's point is very fine, I admit; but a
person who could not see it without spectacles must have very poor
sight. Whereas the last subdivisions of the blood-tubes are so
attenuated, that the best eyes in the world, your own included, cannot
distinguish them. You are astonished at this, and yet it is nothing
compared to what follows.
No doubt you have heard of the microscope,--that wonderful instrument
by which you may see objects a thousand, a hundred thousand, a million
times, if necessary, larger than they really are. With the microscope,
therefore, as a matter of course, we can see a good many of those tiny
canals which elude our unaided sight. But, alas! we discover at the
same time that these are by no means the last subdivisions. The canals
invisible to our naked eyes subdivide themselves again into others,
and these into others again, and so it goes on, till at last--the man
at the microscope can see no more, but the subdivisions still continue.
You were ready to exclaim, at my talking of thousands of canals being
torn by a needle in passing through; but had I even said millions, it
may be doubted whether I should have spoken the whole truth.
Besides, when you consider the office of the blood, you can easily
understand that if there were a single atom of the body left unvisited
by him, that atom could never be nourished. Do I say nourished? I have
made here a supposition altogether inadmissible; it could have no
existence at all, since it is the blood only which produces it.
These imperceptible canals of blood have been called _capillaries_,
from the Latin word, _capillus_, which means a hair; because the
old learned men, who had no suspicion of the wonders hereafter to be
revealed by the microscope, could think of no better way of expressing
their delicacy, than by comparing them to hairs. Very likely they
thought even this a great compliment, but your delicate fair hairs,
fine as they are, are absolute cables--and coarse cables too, believe
me, compared to the _capillary vessels_ which extend to every portion
of your body.
Observe further, that each of these arterial _capillaries_ is
necessarily composed (being the continuation of the large ones) of
three coats enclosed one within the other, which can be perfectly
distinguished in arteries of a tolerable size; add to this that within
these coats there is blood, and in the blood some thirty substances
we know of, not to speak of those we do not know; and then you will
begin to form some notion of the marvels collected together in each
poor little morsel of your body, however minute a one you may picture
to yourself.