trunks separately, it is evident that the relation existing between
them is extremely variable, that it is affected by the manner of the
death, by the diseases that have preceded it, by the habits of the
subject, &c. Let us disregard then, upon this point, as upon every
other, all calculations, even if they have a solid basis, if they do
not lead to a useful result.
Injections are also a deceptive means of estimating this relation;
in fact, they dilate the trunks much more than the branches, and
especially than the smaller branches. The internal jugular injected,
for example, becomes of an enormous size when compared with the sinus
that empties into it. The two venæ cavæ, the azygos, the subclavians,
&c. dilate a little less than the jugular; but their size however is
remarkable when they are injected, in comparison with that of their
branches injected.
_Anastomoses._
The veins communicate in general more frequently than the arteries.
1st. In the ramifications there is a real net work, the anastomoses are
so numerous. 2d. In the smaller branches, they are not so frequent. 3d.
In the branches, they are still less numerous; but still we find many
of them, and it is this that particularly distinguishes these branches
from the arterial, which are almost always separate from each other.
The communications between the branches of the veins unite immediately
in an evident manner the cutaneous to the deep division; thus there
is a communication between the cerebral sinuses and the temporal,
occipital veins, &c.; between the external and internal jugular by one
and even two considerable branches; between the basilic, cephalic, and
their numerous divisions spread upon the fore arm, on the one hand; on
the other, the brachial, the radial and cubital, by different branches
that penetrate deep into the muscles; between the saphena and crural,
tibial, peroneal, by analogous branches.
Though separated, the two great venous divisions can then evidently
supply the functions of each other by mixing their blood. Hence why,
1st, by agitating the muscles of the fore arm, we increase the throw of
blood in venesection, though the muscles do not furnish many branches
to the open vein, which then receives the blood from veins, from which
it is forced out by the muscles; 2d, why in external pressure that
obstructs or even entirely stops the motion of the superficial venous
blood, the circulation continues as usual; why, for example, if a
ligature is left for a long time applied to the arm, the superficial
veins at first swelled, gradually become empty, by pouring their blood
into the deep ones; why, notwithstanding tight bandages in fractures
and luxations, the venous blood returns as usual to the heart, though
it passes in less quantity by the superficial veins. 3d. If a strong
band is applied high up on the leg, and the saphena vein is injected
below, it does not fill above the band, but the injection goes into the
crural. In the same manner the internal jugular may be filled by the
temporal, &c.
The anastomoses between the superficial and deep veins are more
necessary in man than in any other animal, on account of his clothing,
by which the neck, the ham, the arms, &c. are subjected to compressions
that would be dangerous without these anastomoses. We can say that
upon them alone is founded the possibility of a variety of modes in
clothing. That they show in fact that these modes are less dangerous
than some physicians have thought; that the danger of apoplexy from a
tight cravat, of varices from tight garters, &c. is much less than they
have said.
When a single trunk is compressed, the blood passes easily into the
neighbouring ones; but if the compression is made upon all the trunks
of a limb, a certain time is requisite for this fluid to dilate the
anastomoses. It experiences, before this dilatation takes place
completely, a kind of stoppage in the capillary system, a stoppage that
explains the momentary redness of the fore-arm in women, when the arm
is covered with too tight a sleeve, that of the hand or the foot when
the bandages of the fore-arm or the leg are too tight.
The mode of the venous anastomoses is very analogous to that of the
arteries. Sometimes the smaller branches anastomose with the trunks,
sometimes the trunks communicate among themselves.
In the last mode, 1st, there is merely a branch of communication,
and this is the most common case; we see this between the jugulars,
between the deep and superficial veins of the thigh, the arm, &c.
2d. Two branches unite by their extremities and form an arch, the
mesenterics afford an example of this. 3d. Sometimes instead of a
trunk, there is an interlacing of the smaller branches that form a real
venous plexus; such as that which surrounds the cord of the spermatic
vessels.
In general, where there are the most obstacles to the blood, there the
anastomoses are the most numerous. Hence why the veins that surround
the spermatic cord communicate so frequently together, why the smaller
branches of the hypogastric vein which are spread in the bottom of the
pelvis, form there a plexus so extended, that it is a real net work in
which the course of no one branch can be traced, so numerous are the
communications. Notwithstanding this, these two portions of the venous
system are the frequent seat of varices; they are even found more
frequently dilated in the dead body on account of the difficulty the
blood experiences there in rising against its own weight.
This leads us to a general reflection upon the venous system in
relation to the anastomoses, and that is respecting the necessity there
is for the communications being more numerous in this than in the
arterial system. In fact, if we compare the course of the black blood
with that of the red, we shall see that there are many more causes to
modify that of the first.
The black blood evidently obeys its weight in certain cases. 1st. If
we remain standing a short time the veins swell, especially after
diseases in which the forces have been diminished; this swelling
soon disappears if the leg is inclined; it increases if it remains
perpendicular. 2d. There are many cases, in which the forces being very
weak, the circulation cannot go on in perfection, except the legs are
in a horizontal or inclined position. The influence of position upon
many tumours and ulcers of the legs is undoubted. 3d. We know that the
first effect of the attitude with the head reversed, is a giddiness
produced by the difficulty the blood experiences in rising against its
weight. 4th. The valves are particularly destined to counteract the
effect of gravity.
Every violent motion communicated to the black blood, and independent
of gravity, can also disturb the course of this fluid; it is thus that
when we move violently in a circular direction, the venous cerebral
blood receives, if we may so say, a centrifugal motion, which, turning
it from its natural direction, and preventing it from going entirely to
the heart, produces a stoppage of it, and hence the dizziness that is
experienced.
It is not only gravity and every other external cause of motion, which
influence at every moment the motion of the blood in the veins, but
there are also external and internal pressures, and a variety of other
mechanical causes.
On the contrary, that of the arteries is independent of most of the
causes, of weight especially, and of the internal motion. Why? because
the rapidity of the motion is so great which the heart gives to the
red blood, that the influence of gravity and every other analogous
cause is necessarily nothing. Let us take a comparison; the greater
the force with which a projectile is thrown into the air, the less
influence the weight has in making it deviate; in the case of the blood
its influence is still less. If the blood was driven in empty vessels,
gravity would have some effect in the arteries; but in the sudden shock
impressed upon the whole fluid that fills them, a shock, the effect of
which is felt at the extremities at the same time as at the origin,
it is evident that its effect is nothing. For an opposite reason, we
can understand why it is so powerful in the veins, in which there is
no agent of impulse, in which the parietes and capillary system alone
produce the motions, where the motion is consequently slow, &c.
From these considerations, it is easy to see the reason of the very
different arrangement that the arteries and veins exhibit in their
branches, as it respects anastomoses, which are as rare on one side as
they are frequent on the other.
IV. _Termination of the Veins._
The veins terminate by two principal trunks, the superior and inferior
venæ cavæ. There is also another, viz. the coronary vein, which empties
separately into the right auricle; but as this trunk only brings back
the blood that went to the heart, we shall pay but little attention
to it in our general remarks, and but little to those small venous
branches that empty separately from it into the same auricle.
Some authors have thought, that the two venæ cavæ were continuous
and formed but one vessel; but it is easy to see how different their
direction is. It is particularly in the fœtus, that their separation
can be well perceived, since one corresponds with the right auricle,
and the other with the left. There is behind the right auricle a kind
of continuity of the membrane between the one and the other; it is the
membrane of the black blood that is common to them, and which passes
from the inferior to the superior; but in this respect there is no more
continuity between them, than between the right side of the heart and
the pulmonary artery, between the left and the aorta, &c.
By considering the whole of the trunks and the branches as a cone, we
can say that there are two great venous cones distinct from each other;
one for all the parts which are above the diaphragm, the other for all
those that are below it.
The superior vena cava does not answer, then, entirely to the union
of the arteries that form the aorta of the same name, which is only
destined to the neck, head, and superior extremities, whilst the
other belongs moreover to the chest by the vena azygos. For a contrary
reason, the descending aorta has a destination much more extended than
the inferior vena cava.
The limit between the two cones of the ascending and descending venæ
cavæ, is placed at the diaphragm. It is especially in this respect that
we can say that this muscle divides the body into two parts. Has not
this arrangement some influence upon the difference that is observed in
certain diseases between the superior and inferior parts? Should not
this cause be connected with those pointed out under the article upon
the fœtus? As yet there is nothing certain with regard to this, but I
think it not improbable.
Though forming each a distinct cone, the two venæ cavæ communicate,
however, especially in the neighbourhood of their common limit, that is
to say, in the neighbourhood of the diaphragm; the azygos is the great
means of communication. We know, in fact, that its trunk opens into
the right renal, into the vena cava itself, or into some of the lumbar
veins, and that the semi-azygos that arises from it, goes also to the
left renal or to the lumbar of the same side. This anastomosis is very
important; physicians have not paid sufficient attention to it. It
proves that when an obstacle is situated in the trunk of the inferior
vena cava, a great part of the blood of this trunk can flow into the
superior. Much has been said of the compression of this trunk by the
enlargements of the liver, in the production of dropsies. But, 1st, it
is ascertained by the numerous examinations of dead bodies in modern
times, that the production of these diseases belongs to every kind of
organic affection; that the lungs, the heart, the womb, the spleen, &c.
can likewise occasion them in the latter periods of the alteration of
their texture; and that, in this respect, they are but a symptom in the
greatest number of cases, and a symptom wholly disconnected with any
sort of compression. 2d. By supposing that the liver could exert upon
the vena cava an analogous compression, in the place where this vein
crosses its posterior part, it is evident that the anastomoses of which
I have just spoken, would prevent the effect of this compression, at
least in great measure.
By supposing that an obstacle was encountered in the vena cava
superior, the same anastomoses would undoubtedly answer the same end;
but as the azygos is inserted very near the auricle, as the course of
the trunk of the vena cava superior is consequently very short, it is
evident that it is especially to counteract the obstacles the inferior
may experience, that these anastomoses have been established.
When the blood of this vein passes thus into the superior, it goes
through certain branches in a direction opposite to that which is
natural to them. For example, suppose that the anastomosis takes place
in the renal, which most often happens; then the blood of the trunk
of the vena cava enters by one extremity of this vein; that from
the kidney comes by the opposite extremity, and both pass into the
azygos. A similar motion evidently supposes the absence of valves in
the renal, from the vena cava to the insertion of the azygos. Now the
renal veins never in fact have these folds; the capsular, the adipose
of the kidney, all the lumbar, are also destitute of them, as Haller
has seen, and I have ascertained it to be uniformly so. This absence of
valves at the places of the anastomoses of the azygos, is a remarkable
phenomenon; it proves very well the use that I attribute to the
communication of the two venæ cavæ by means of this.
ARTICLE SECOND.
ORGANIZATION OF THE VASCULAR SYSTEM WITH BLACK BLOOD.
I. _Texture peculiar to this organization._
This organization is nearly the same for the whole system, in the
common membrane that forms the great canal in which the black blood is
contained; but it differs in the textures that are connected exteriorly
with this membrane. In the heart the texture is fleshy; it is analogous
to the texture of the divisions of the aorta, in the pulmonary artery;
it has a peculiar character in the veins; it is this that will now
particularly engage our attention.
_Membrane peculiar to the veins._
In order to see this membrane, it is necessary to remove, 1st, the
loose cellular texture that unites the veins to the neighbouring parts;
2d, the cellular layer of a peculiar nature that immediately covers
them, and of which we have spoken in the article upon the cellular
system. Then we distinguish in the great trunks, longitudinal fibres
all parallel to each other, forming a very fine layer, often difficult
to be seen at first view, but always having a real existence. When the
veins are much dilated, these fibres being more separated, are less
evident than in a state of contraction. These longitudinal fibres are
seen more clearly in the trunk of the inferior vena cava than in that
of the superior. In general it may be said, that they are also more
marked in all the divisions of the first than in those of the second;
dissection has convinced me of this. Undoubtedly this arises from the
greater facility that the blood experiences in circulating in the
second than in the first of these veins, in which it mounts against
its own weight; this is moreover a proof that man was designed to go
erect.
I have uniformly made another remark, it is, that in the superficial
veins these fibres are much more evident than in the deep-seated ones;
the internal saphena is a remarkable example of this. It suffices to
open it in its course, to see very distinctly its fibres through the
common membrane, especially if it is a little contracted. By cutting
the crural vein to compare it with this, it is easy to perceive the
difference, which arises without doubt from this circumstance, that the
neighbouring parts assist the circulation in the deep veins, whilst
there is less of this assistance given to the superficial ones.
The branches have fibres in proportion greater than the trunks; hence
the proportional excess of the thickness of their parietes, their
greater resistance to the blood, their less frequent dilatation, &c.
At the place where any branch arises from a trunk, we observe that the
fibres change their direction and go upon the branch, a circumstance
that distinguishes them from arterial branches, whose fibres are not a
continuation of those of the trunk.
Venous fibres oftentimes approach each other, are united, and give
a greater thickness to the vein; this is frequently observed at the
origin of the saphena. I have also seen this arrangement in the
hypogastric vein; Boyer has likewise noticed it.
In general, the venous fibre, except in these places, is remarkable
for its delicacy, for the little thickness that it consequently gives
to the membrane that it forms. The peculiar membrane of the arteries
infinitely exceeds that of the veins in this respect; it is this
delicacy that favours to a great degree venous extensibility. Observe
that the structure of each kind of vessels is adapted to their peculiar
circulation. If the blood circulated in the veins with parietes like
those of the arteries, its motion would be continually disturbed. A
thousand causes retard the venous blood; when its motion is languid,
the capacity of the vessels is increased; now, the arterial textures
not allowing of this dilatation, it is evident that the circulation
would be interrupted. If then the agent of impulse, placed at the
commencement of the arteries, requires a firm and unyielding texture,
the slow motion of the blood in the veins, the frequent causes that
retard its progress, demand a texture of an opposite character.
What is the nature of the venous fibre? Its appearance, its want of
elasticity and brittleness, its great extensibility of texture, its
softness, its colour, its direction, distinguish it completely from the
arterial fibre. Is it muscular? it does not appear to be irritable,
and it does not look like the muscular fibres. I believe that it is of
a peculiar nature, essentially different from that of all the other
textures, having its peculiar properties, life and organization; I do
not think it capable of much motion. We have, however, but few data
upon this point.
The venous fibre, though infinitely more extensible than the arterial,
is also more resisting; it will support without breaking, very
considerable weight. The experiments of Wintringam have proved this. In
the superficial and inferior veins especially, this is very remarkable.
There is a great difference in individuals as it respects the venous
fibres. In some they are very apparent; in others, they are hardly
distinguishable upon the great trunks; but then they are always very
evident in the branches, particularly in the superficial ones.
There are places in the venous apparatus where we cannot discover
either external fibres, or external cellular texture; this is the
case with the cerebral sinuses, which have the following arrangement.
The jugular vein at its sinus, loses its peculiar texture, and keeps
only the common membrane, which, entering the lateral sinus, lines
it, and extends below into the inferior longitudinal sinus, and
above into the superior; in a word, into all the sinuses of the dura
mater. Hence every sinus supposes, 1st, a separation of the layers
of the dura mater; 2d, the common membrane of the black blood lining
this separation. It is not then upon the dura mater that the blood
circulates; it is upon the same membrane that it flows elsewhere; it
is easy to establish this fact in the superior longitudinal sinus.
This sinus is triangular when considered in relation to the separation
of the layers of the dura mater; but in opening it, we see clearly,
that the common membrane, by passing over its angles, makes it round;
this is very evident. It is easy, also, in many other sinuses, to
separate in certain places this membrane from the dura mater; but
in the greatest number the adhesion is close, like the union of the
arachnoides with the internal surface of the dura mater. This common
membrane of the black blood is spread over the folds of the superior
longitudinal sinus; it forms a singular net-work, which I shall
describe in the cavernous sinuses.
From this general outline, it is evident that the coats of the dura
mater supply in the sinuses the place of the venous fibres and their
external dense cellular texture; the common membrane is always the
same; but the texture that is added to it externally is different.
At the place where each cerebral vein opens into a sinus, the common
membrane of that sinus connects itself with it in its passage and lines
it to its extremities. I know of no author who has thus considered the
cerebral sinuses, as having the common membrane of the black blood
extended into all the separations of the dura mater. How little soever
we examine the internal surface of a sinus, it is easy to see that
this surface differs as much from the texture of the dura mater, as it
resembles the internal surface of the veins.
The cerebral veins, of which the sinuses are the terminations, are
analogous to the arteries of that part in the extreme tenuity of their
parietes, a tenuity that appears to be owing to the absence of the
cellular coat, and which is so great, that you might believe that there
was only a common membrane.
There are no circular fibres in the veins.
_Common Membrane of the Black Blood._
This membrane generally extended from the general capillary system to
the pulmonary, is every where nearly of the same nature. It differs
essentially from that of the red blood in a great number of respects.
1st. It admits of much greater distension; consequently it is less
brittle. Tie a vein, and it will not break, unless the constriction
be excessive; it is almost as pliable as the cellular coat. This
pliability renders it much easier of dissection than the common
membrane of the arteries. 2d. It appears to be much more delicate; we
have a proof of this in the valves, which at first view are hardly
visible from their extreme tenuity, when they are lying against the
external surface of the vein. 3d. This common membrane is never
ossified in old age, like that of the arteries; its organization
seems to resist the deposition of phosphate of lime. When it does
take place, it is an unnatural state; whereas the ossification of the
common membrane of the red blood is almost a natural state in old age,
as I have before observed. This difference between the two common
membranes of the black and red blood, gives a distinctive character to
the diseases of the heart. We never see ossification in the tricuspid
valves, or in the semilunar valves of the pulmonary artery, whilst
they are so frequent on the left side; this is the uniform result
of observations made at the Charity; in the bodies of old people
dissection has always shown me the same thing. So the pulmonary artery,
though analogous to the aorta by its peculiar membrane, is never the
seat of these ossifications, because the common membrane differs
essentially from its own. This single phenomenon, so striking in both
these membranes, would incontestibly prove their organic differences,
while it establishes the necessity of considering them in a general
manner, whether, in the black blood, they line the veins, the pulmonary
artery, and the right side of the heart, or in the red blood, they are
spread upon the arteries, the left side of the heart, and the pulmonary
veins.
_Of the Valves of the Veins._
The common membrane of the black blood has numerous folds that are
called valves. These folds are wanting in the pulmonary artery, except
at its origin, where we find the semilunar valves; in the heart, the
tricuspid valves are in part formed by this membrane; but the venous
valves are wholly made by it; it is with them that we are particularly
concerned.
The form of these valves is parabolical; their convex edge is
attached, and most remote from the heart; their straight edge is
loose, and nearest that organ. There is between them and the vein a
space analogous to that of the semilunar valves of the aorta and the
pulmonary artery. They have not, like these valves, a granulation upon
their loose edge. On a level with the attached edge, the venous texture
is firmer; there is a kind of hardening, which makes a prominent line
of the same curved form as that edge. This hardening supports the
valves, like the one corresponding to it in the semilunar valves. It
appears to be of the same nature as the venous texture, the direction
of whose fibres are changed to form it. When the common membrane
arrives at this prominent line, it is folded to form the valve; so that
it seems to be made of two layers, which are separated with difficulty,
from its extreme tenuity.
The venous valves exist in the inferior vena cava, as in the superior.
In the first, the divisions of the hypogastric, of the crural, tibial,
internal and external saphena veins, &c. are full of them. The second
presents many of them in the external jugular, in the azygos, in the
facial veins, in the veins of the arms, &c. Many veins have no valves,
as we see in the trunk of the inferior vena cava, in the emulgents, in
the cerebral sinuses, &c.
The size of the valves is always in proportion to that of the trunks
in which they are found; very distinct in the azygos, less so in
the saphena, and still less so in the plantar veins. If we compare
them with the caliber of the trunk they occupy, we shall see that
sometimes they can entirely obliterate its cavity, and that at others
they are too narrow to produce this effect. All authors have noticed
this arrangement; they have thought that it depended upon primitive
organization; but I am convinced that it arises wholly from the state
of dilatation or contraction of the veins. In the first state, the
valves being drawn and not dilating in proportion, become smaller
compared to the caliber of the veins, whose cavity they cannot entirely
obliterate when they fall down. In the second state, as they do not
contract in proportion to the vessel, they become more lax and are
capable of closing it completely. All that has been written by authors
upon the size of the valves, depends then wholly upon the state of the
veins at the moment of death. This is so true that they appear large if
the animal dies of hemorrhage, and small if he dies of asphyxia. I have
twice proved this fact.
From what has just been said, it is evident that the reflux of black
blood takes place much easier and extends much further when the vein
is dilated; and that consequently the first pulsation, the effect of
this reflux, does not extend as far as the second, nor this as far as
the third and so on. It is this that happens in the cases that we have
spoken of before. The reflux never extends to the capillary system,
especially in parts at a distance from the heart, because there being
many valves and each checking in a degree the blood, it soon stops by
losing all the motion received from the heart.
The existence of valves is generally constant, but their situation and
number are very variable. Sometimes they are very near each other, at
others at a greater distance, in this respect there is a great variety.
Generally in the small trunks they are nearer, and at a greater
distance in the large ones.
They are rarely arranged three by three, most often in pairs, and
sometimes they are insulated; this is the case especially in the small
vessels, in those of the foot, of the hand, &c. We find in the works of
Haller very minute descriptions of the general arrangement, form and
position of the vascular folds of which we are treating.
These folds perform, as we shall see, an important part in the venous
circulation; by them we are enabled in most operations, to dispense
with tying the venous trunks, if they are not very considerable. In
fact, without them, the blood poured by the collateral branches into
the open vessel, would easily escape by a retrograde motion, and then
we might fear the effusion of all that, which passes in the whole
course of this vessel, whilst now none can escape except what flows
between the opening and the first or second valve.
The valves constitute an essential difference between the veins and
the arteries. Let me observe, that the want of them in these last
vessels is a proof in addition to what has been already named, of
the absence of vital contractility in their texture. In fact if they
contracted like the heart to drive the blood, this fluid, tending as
much to return towards the heart by the effect of this contraction, as
to go to the extremities, there would be at intervals in the arterial
tubes, valves to counteract this first motion; now we only see them
at the origin of the aorta; why? because it is only necessary in the
arteries to resist the effect of the contractility of texture, which,
exerting itself without a jerk, by a mere contraction, can return but
very little blood to the heart. A single obstacle at the beginning of
the arterial system, is sufficient then to prevent the derangement
of the circulation, which might be the effect of the reflux caused
during the systole by the contractility of texture of the arteries,
a reflux which only takes place in certain cases; for ordinarily the
return of the arteries upon themselves, is produced as I have said, by
their containing less blood, which has been driven through them during
the diastole. In order that this reflux might take place, it would be
necessary that the effect of the contractility of texture should in the
systole exceed what the arteries have lost of blood in the diastole.
_Action of re-agents upon the Venous Texture._
This texture exposed to drying, becomes yellowish, remains pliable and
can be bent in any direction; so that the dried venous bands, might in
this respect, be applied to uses, to which the arterial could not in
the same state.
This texture becomes putrid also more easily than the arterial, but
less so than the others, particularly the muscular. To ascertain
this, I have exposed at the same time, venous trunks and portions of
intestines of fine muscular layers, to the contact of a moist air.
It resists maceration less than the arterial texture, but more than the
others; water in which it has been macerated by itself is much less
fetid than that in which an equal portion of muscular texture has been
placed.
The horny hardening of the venous fibres is very evident when they are
plunged into boiling water or the concentrated acids. They contract
then more than half, at the same time they become more evident; in
this way they can be studied better; I have used it often; their
contraction thickens the parietes of the vein. When they are hardened
in this way, if they remain in boiling water or the acids, they become
soft very soon in the second, more slowly in the first. Boiling acts
upon them quicker than upon the arterial fibres; they can also be
reduced by long ebullition to a pulpy state, to which we can never
bring the arteries.
The caustic alkali seems to have a very remarkable action upon the
veins. After remaining a short time in a solution of this alkali, they
become diaphanous, diminish in size, do not entirely dissolve, it is
true and become liquid, as in the acids, but evidently lose their
elementary principles, give a remarkable precipitate, and always render
the liquor less strong, by the new combinations which it forms.
II. _Parts common to the organization of the Vascular System with Black
Blood._
_Blood Vessels._
The veins have in their texture little arteries and veins, which take
very much the same course as in the arteries. They ramify at first in
the cellular membrane, send small branches to the neighbouring parts,
then penetrating the venous fibres, wind there in a thousand different
directions and finally terminate about the common membrane, which when
injected has appeared to me to receive more than in the arteries.
_Cellular Texture._
The veins, like the arteries, have around them two kinds of cellular
texture; one which is exterior and of the same kind as that which is
found in the interstices of all the organs; it contains fat and serum,
and serves only to connect the veins with the adjacent organs; the
other dense and compact, forms for them a proper coat. No author has
yet distinguished the cellular system of this particular texture from
that which is generally spread over the organs, though it differs from
it so essentially in its filamentary texture, in its dryness, its
uniform want of fat and serum, its remarkable power of resistance, &c.
When we raise it, by tearing it with the fingers from the veins, it
appears as if it was formed of an infinite number of little filaments
interwoven with each other.
After having formed this external covering to the veins, this cellular
texture of a peculiar nature analogous to the sub-arterial, sub-mucous,
&c. passes between the longitudinal venous fibres, separates them,
forms for them a kind of sheath, and terminates in the common membrane,
which appears to contain it in its texture, and which owes perhaps in
part to this circumstance, the great extensibility that it possesses.
I would observe that the presence of the cellular texture in the venous
parietes is a distinctive and striking character that distinguishes
them from those of the arteries, with which their texture has in other
respects no kind of analogy.
_Exhalants and Absorbents._
It appears that there is no exhalation upon the internal surface of
the veins. This surface is always moist in the dead body, though the
vessels are empty; but I attribute this phenomenon, as in the arteries,
to a transudation that has taken place after death. If there was in
fact a fluid exhaled, it would prevent the adhesions of the venous
parietes, when during life the blood ceases to flow through them. Now
every vein that is empty is obliterated into a sort of ligament, like
the arteries in similar cases.
There is no more absorption upon the internal surface of the veins,
than exhalation. To satisfy myself of this fact, I have tried upon
the external and internal jugular veins, the same experiment before
noticed, as having been made upon the carotid artery; I obtained the
same result and drew from it the same conclusion. I have been induced
to make these experiments, from the opinion of many distinguished
anatomists, who thought that the absorbents arose immediately from the
veins and the arteries. It is possible that this is the case in the
smaller branches, in the capillary system especially, as I shall say in
the absorbent system; but I do not believe that any thing similar can
be demonstrated in the trunks.
It appears then that the exhalants and absorbents of the venous
parietes, like those of the arterial, are confined to the nutritive
functions, and that they are consequently few. This remark is
applicable not only to the veins, but to the whole of the vascular
system with black blood.
_Nerves._
1st. The veins differ essentially from the arteries by the few nerves
of the ganglions that accompany them. Whilst these nerves form for most
of the arteries a kind of covering, they are scarcely spread at all
upon the veins. By laying bare the venæ cavæ, jugulars and azygos, it
is easy to observe this. 2d. The side of the heart with black blood,
receives as many nerves as that with red; this proves that they have no
influence upon the contraction, as it is evidently weaker on the right
side than the left; whereas if it was produced by the nerves it would
be equal, as there is an equal distribution of them. 3d. The pulmonary
artery has but very few nerves. I know not as yet the relation that
exists between it and the pulmonary veins in this respect.
It appears from this general survey, that the system with red blood has
many more nerves than that with black. In fact being nearly equal at
the heart, and the difference being very sensible in this particular
between the aortic arteries and the veins that go to the right
auricle, although the pulmonary artery may have a few more than the
corresponding veins, which I think very probable, yet the short course
of these vessels would not prevent the disproportion from being very
apparent.
ARTICLE THIRD.
PROPERTIES OF THE VASCULAR SYSTEM WITH BLACK BLOOD.
The veins are in general but little elastic, soft, and loose; they
partake of the character of many of the animal textures, and are
essentially distinguished in this respect from the arteries, which
as we have seen are very elastic. We shall now treat of the vital
properties and the properties of texture in these vessels.
I. _Properties of Texture. Extensibility._
The veins have in regard to this property, an arrangement entirely
opposite to that of the arteries, which are very extensible
longitudinally, but very little so transversely.
The veins stretch but little in the first direction. When drawn out
of a stump after amputation upon the dead body, they lengthen but
little in proportion to what they dilate in varices, though here they
experience an actual increase of size. Perhaps however this depends
less upon the deficiency of extensibility of texture, than upon the
circumstance that the folds are less evident than in the arteries, and
of course the development is less. Whatever may be the cause, the fact
is certain and uniform.
Few organs, on the other hand, exhibit a greater degree of
extensibility transversely, than the veins. In the dead body, they can
be enormously dilated, by injections of air, water, fatty substances,
&c. In the living, we know the varicose dilatations, which arise in the
great trunks, from the obstacles to the course of the blood in the
lungs. While the arteries do not appear very often more than to double
their diameter without breaking their common and peculiar membrane, the
veins treble, quadruple, and even quintuple their diameter without this
rupture's taking place.
We have however numerous examples of this accident. Haller has related
many in his great work. We see these ruptures take place during
pregnancy in the veins of the lower extremities; there are examples of
them also in the external veins of the head in violent headaches. We
have seen the venæ cavæ, the jugulars, the subclavians suddenly break
and produce death. Every one knows of the hemorrhages that arise from
the rupture of the hemorrhoidal veins, &c. I think that the extreme
tenuity of the parietes of the cerebral veins exposes them to being
frequently torn by blows upon the head, wounds upon that part, &c. When
there is an effusion in the tunica arachnoides, it can certainly come
from no other source than the venous trunks, which being surrounded
by a fold of the arachnoides, pass through this cavity to go to the
cerebral sinuses. Now we know that this case is very common, and
that it even takes place at the same time with that, in which the
dura mater being detached from the cranium, is found separated by an
effusion. Is not apoplexy a sudden rupture of the venous extremities?
I have already observed that we have no data upon this point. All
these cases are very different from arterial aneurism; they often take
place when the dilatation is infinitely less than in many instances
where the veins remain whole. Very commonly this does not happen. The
whole of the vein, with the cellular tunic containing it, bursts. The
arterial rupture in true aneurisms, is on the contrary uniform; when
the dilatation is carried to a certain point it always happens. The
two arterial coats break easily, the cellular remains whole. I do not
believe that there is a solitary instance of a great aneurism, without
rupture. Why? because the arterial extensibility can only yield to
a certain point. The ruptures take place then from a want of this
property; they are disconnected with this cause in the veins. We do not
know yet how they are produced. In a great number of cases certainly,
there is an affection of the venous texture; this is undoubtedly the
case in hemorrhoids, &c. Let us be content to point out the differences
between arterial and venous ruptures, and wait till further observation
shall discover to us all their causes.
If we bear in mind, that the arterial fibres are very numerous and
all circular, that the venous, on the contrary, are on the one hand
longitudinal where they exist, and on the other that they are very
thinly scattered on their vessels, we shall then see why the first
resist much longer a distension in the direction of their diameter
than of their axis, and why the opposite phenomenon is observed in the
second, though much less decided.
_Contractility._
This corresponds with the extensibility. Slight in the longitudinal
direction, much greater in the transverse. 1st. It produces the
contraction upon themselves, of the parietes of the umbilical vein,
of any trunk that is tied, &c. 2d. It produces in a trunk that is
pricked, the sudden evacuation of the blood contained between the
two ligatures by the return of the parietes upon themselves. 3d. It
manifests a decided influence on the flow of blood in venesection. 4th.
The numberless varieties of caliber that the veins exhibit after death,
according to the quantity of blood they contain, are the result of
their extensibility and contractility of texture. 5th. During life, the
superficial veins appear very various; dilated in summer, contracted in
winter, expanded in the warm bath, as we see the saphenas, especially
in pediluvium, lessened in the cold bath, prominent by a long
continued perpendicular position, flattened by a horizontal one, &c.
they present to him who observes them, at different times, numerous
varieties. I very much doubt whether those who have calculated so much
the capacity of the vessels, the velocity of the blood, &c. would have
undertaken their labours, if they had opened many bodies, or made many
experiments upon living animals; now all the varieties depend upon the
extensibility and contractility of texture.
II. _Vital Properties._
_Properties of Animal Life._
Have the veins sensibility? The following is the result of my
experiments upon the subject. 1st. Irritated externally by any
mechanical instrument, pain is not produced, as Haller has seen; 2d, a
ligature put upon them gives no pain, whether it is done upon living
animals, or in certain surgical operations, in great amputations, for
example, in which it is recommended to tie the vein as well as the
artery. 3d. Irritated internally, they exhibit the same phenomenon. I
have many times pushed a stilet very far into one of these vessels,
without making the animal cry out. I would observe also, that this
is a good method of examining the sensibility of the heart, without
producing in the chest a disturbance, that would increase, diminish,
or alter this property in any manner, by the general derangement that
it would occasion in the economy. I force then a long stilet into the
right external jugular vein, opened as it is in the operation for
bleeding. This stilet goes to the heart, without any accident, by
straightening out the venous angles. The animal oftentimes gives no
sign of pain; sometimes, however, he does; the motion of the pulse is
always accelerated. We might easily reach in a man, without accident,
with a stilet, the right side of the heart, by introducing it into the
right external jugular vein. Why, in certain asphyxias, in syncopes
which resist all other stimulants, &c. might we not employ this method
to re-animate the action of the heart? 4th. When we inject a foreign
fluid into the veins, however irritating it may be, the animals rarely
show any sign of pain. Urine, bile, wine, the narcotics, &c. are
transfused with impunity in this respect. 5th. On the contrary, when
a bubble of air enters them, the animal cries out, is agitated, and
struggles before dying; is this owing to the contact of the fluid upon
the common membrane? I believe not; for usually there is an interval
between the cries and the injection of the air. It is possible that
the pain happens at the instant when the air strikes the brain, after
having passed through the lungs, a passage which is constant, as I have
observed elsewhere.
There is evidently no animal contractility in the veins. The same
experiments that demonstrate its absence in the arteries, prove it also
as it respects the veins. I have made them at the same time upon both
kinds of vessels. I refer, then, upon this subject to the preceding
system.
_Properties of Organic Life. Sensible Contractility._
This property does not appear to be an attribute of the veins. Haller,
by irritating them in different ways, perceived no sensible motion in
them. I have usually made the same observation, whether I employed
internal or external irritation.
It has appeared to me, however, in two or three cases, that a manifest
contraction took place. As the venous fibres are only longitudinal, and
as they are very few, it is evident that in admitting that they are
muscular, it would be very difficult to observe the effect of irritants
applied to them, though it might be real. The question is not, then,
fully settled, though I incline much more to the belief that there is
no venous irritability. As the venæ cavæ have evident fleshy fibres
at their origin, it is evident that they possess at that place the
contractility of which we are treating.
A proof of the great obscurity of the sensible organic contractility
in the veins, is, that it is never increased in disease. All the
organs, in which this property exists, are remarkable for its frequent
increase, which constitutes in the heart the quickness and the force
of the pulse, in the stomach vomiting, in the intestines diarrhœa, in
the bladder incontinence of urine, especially in children, &c. Now the
veins never exhibit a derangement, which, corresponding to these, would
make us believe in the existence of a power of which this derangement
is the excess, if I may so say.
Observe, that this observation is also applicable to the arteries;
never in a determinate portion of the arterial system, do we see this
local disturbance, this insulated derangement, which certain portions
of the intestinal canal sometimes exhibit. The irregularity of the
motion of the blood is always general, because it arises from a single
cause, viz. the irregular impulse of the heart.
Observe, that this way of discovering the presence or absence of this
or that vital force in a part, by the affections which increase that
force there, deserves an important consideration in the examination
of these forces. Authors have not employed this method of discovering
them, of pronouncing consequently upon their presence or absence in the
organs.
_Of the Venous Pulse._
The pulsation that the veins have under certain circumstances, must not
be taken for an effect of the venous irritability. It is an effect of
the reflux of the blood, which not being able to go through the lungs,
stagnates in the pulmonary arteries and in the right side of the heart;
so that when this contracts, as the blood finds an obstacle in the
ordinary course, it flows back whence it came, as when the aliments
are unable to pass down, they take the other direction. This reflux
takes place, to a certain distance, notwithstanding the valves; it is
often very evident in the jugular vein, when animals, submitted to
experiments, breathe laboriously; then it is discontinued; it takes
place three or four times, then ceases, and returns irregularly; it
is observed also in the last moments of life, when the lungs are
embarrassed.
The vein is then sensibly dilated; then it contracts. But if you
apply the finger above, you do not experience a sensation analogous
to that of the pulse; you will perceive only a wave of blood which
flows back. The reason of it is plain; 1st, there is no locomotion;
2d, as the venous parietes are loose, they could not strike the finger
sufficiently strong, if there was a similar change of place. Observe,
that it is less the blood than the artery itself which by its firm
texture gives the sensation of the pulse; if it could straighten itself
when empty, as it does when it is full, it would produce nearly the
same sensation; this is a remark that should be added to what I have
said upon the pulse in the preceding system.
The contraction of the veins in the motion of the reflux, of which we
are treating, is only the contractility of texture. When the heart
ceases to propel the blood in its cavity, it contracts, after having
been dilated; it is nearly the same in the dead body, in which we fix
a syringe in the veins; when they are very full of water, if we draw
back the piston a little, immediately the fluid returning, the vein
contracts; it is as when it contracts from a puncture that evacuates
the blood; this does not imply any irritability.
I believe that sometimes this reflux may depend upon an irregular
motion of the heart, which contracts in an opposite direction to the
ordinary one, though there is no obstacle in the lungs. What induces
me to think so, is, that frequently in experiments, at the moment the
animal begins to suffer much, the reflux takes place before the lungs
have had time to be disturbed. A very remarkable thing in experiments
is the quickness with which pain disturbs the motion of the heart,
accelerates it, renders it irregular, &c. We can always at will hasten
respiration, by making the animal suffer; now the acceleration of the
pulse is always prior to that of respiration, which appears to be
determined by it. I am persuaded that if the diseases of the heart were
as frequent on the right side as the left, they would often produce
this reflux and this pulsation of the veins.
The limits of the reflux of the venous blood vary. Haller has observed
it as far as the iliacs. In general, it rarely goes beyond the great
trunks, on account of the valves. I have demonstrated in my Researches
upon Death, that the colour of those who die of asphyxia, of those who
are drowned, &c. does not depend on this, because it cannot evidently
extend to the capillary system, which receives the black blood that
colours it, from the arteries that then circulate that kind of blood.
The reflux of the black blood in the veins, produced in the preceding
cases, either by an obstruction in the lungs, or by a sudden
derangement in the action of the heart, takes place in a natural
state, though in an infinitely less degree. In fact, when the right
auricle contracts, all the blood does not pass into the corresponding
ventricle; the veins being open, a portion flows back into them. It
is difficult to determine the extent of this natural reflux, of which
all authors have spoken. When the thorax is opened, we observe it
distinctly; we might then ascertain its extent; but in this case,
respiration not being performed as usual, it is evident that we cannot
judge by it of what ordinarily takes place.
_Insensible Contractility._
This property, which, like the preceding, is inseparable from the
organic sensibility, exists in the veins as in the other parts; it
presides only over nutrition; it appears more evident than in the
arteries; at least the diseases which particularly increase it are more
frequent in the veins. The texture of these vessels is often inflamed.
1st. Bell relates cases of it, the effect of external violence. 2d.
Every one is acquainted with the inflammation of the hemorrhoids. 3d.
The cicatrization of venous wounds after bleeding is a product of
inflammation. Without doubt this cicatrization is promoted by the want
of impulse, to which the arteries are subjected; but certainly these
last would not in like circumstances heal so fast, if they did at
all. When an artery has been tied, it is necessary that its parietes,
inflamed by the action of the thread, most often cut by it, and brought
into contact, should form adhesions, that the cure may be complete, and
the ligature come off without danger. Now, nothing is more difficult
and slower than their adhesion, from the difficulty with which the
arterial texture inflames. Hence the frequency of hemorrhage after the
operation for aneurism and other great operations. The blood often
bursts out at the end of twenty, thirty, or forty days; the surgeon
should always be upon his guard when he has tied these great trunks,
from the want of disposition in the arterial texture to inflame.
Frequently when the artery is obliterated, it is not by inflammation.
Whilst the ligature stops the blood, the portion of artery comprised
between it and the first collateral branch, closes gradually by the
contractility of texture, and forms a kind of ligament, which arrests
the blood after the thread has fallen off. I do not know but that
these cases are more numerous than those of inflammation. Now the
veins always adhere soon when they are tied; their wounds cicatrize
immediately. In great wounds it is almost always useless to tie them at
the first moment, on account of the valves, as I have said above, and
afterwards, because the cut ends contract, and soon inflame and adhere.
If there are venous hemorrhages, it is at the time of the injury, and
not as long after as in the arteries.
Every thing proves, then, that the vital activity is much greater in
the venous than in the arterial system, in respect to the tonic powers.
The absence of the cellular texture in the second and its presence in
the first, may have an influence upon this phenomenon.
_Observations on the motion of the Black Blood in the Veins._
From what has just been said, it appears, that the blood is beyond the
influence of the heart when it arrives in the veins. It is evident,
then, that the veins can have no pulse. 1st. This phenomenon depends
upon a single impulse, suddenly received by the contraction of the left
ventricle; now, the blood is poured from all parts by the capillary
system into the veins, this agent of impulse is wanting; the cause of
the pulse does not exist in the veins. 2d. The necessary conditions for
its production in the texture of the vessels in which it takes place,
are elasticity and resistance, which are also wanting in the veins.
They are only susceptible, then, either of a pulsation which occasions
the reflux of the blood in the derangement of the lungs, or in the
irregular motions of the heart, or of an undulation of which they are
the seat, when arterial blood accidentally circulates in them; now, in
either, the heart is the principle of motion, and it could not exist
without it.
This is what takes place in the venous motion. The capillary system, by
its insensible contractility, pours continually into the venous system
a certain quantity of blood. This fluid, added to what is already
there, communicates a general motion to it. Now, as the whole venous
system is constantly full, it is necessary that while the fluid enters
at one side it should go out at the other; if not, the venous parietes
would dilate; but, as they have a resistance by which they can act to a
certain point upon the blood, this fluid not being able to dilate the
veins, flows towards the heart.
The impulse given by the insensible contraction of the capillary
system, is too weak, however, to extend instantaneously from one
extremity of the veins to the other, especially where the blood rises
against its weight. As this fluid enters these vessels, the weight
of that which is before it not being overcome, it would produce a
general dilatation, and the blood would not reach the heart; but the
valves counteract this, by supporting at short distances the column of
blood. Weakness of the venous parietes and the existence of valves are
necessarily connected. If the veins were as strong as the arteries,
unable to dilate when the blood enters them, they would necessarily
transmit the surplus to the heart, if they were destitute of valves;
but on the other hand, their circulation would be every instant
embarrassed.
It appears that it is not only the insensible contraction of the
capillary system which propels the blood in the veins; but that the
ramifications of these vessels have a kind of absorbent power, by which
they draw blood into this system. Now the insensible motion produced
by this power tends evidently from the ramifications towards the
trunks, as in the lymphatics; then, when, on the one hand, the blood
is propelled in the veins, and, on the other, as it were, attracted by
them, it is evident that the primitive source of motion that it obeys,
is in the capillary system.
This impulse communicated to the blood, exceeds but very little
the resistance which this fluid experiences in its motion; so that
the least resistance deranges this motion. Hence, as we have seen,
the necessity of anastomoses. Hence also the necessity of other
assistance to aid this motion, such as, 1st, the muscular action, the
influence of which we cannot doubt, when we see the flow of blood in
venesection accelerated by the motion of the muscles of the fore-arm,
the palpitations of the heart, produced by the blood that flows there
after a rapid circulation; when we observe that varices are as rare
in the veins situated among the muscles, as they are common in the
sub-cutaneous ones, &c.; 2d, the pulsation of those arteries which
are in many places joined to the veins, and which communicate to
them a kind of motion; 3d, the motion of certain parts, like that
of the brain, which continually rising and falling, accelerates the
circulation of the blood of the sinuses in an evident manner; so
also the constant locomotion of the gastric viscera, propels it in
the veins of the abdomen, and that of the pectoral viscera, in those
of the thorax. It is so true that the veins derive assistance to
their circulation from external motions, that if a limb is a long
time immoveably fixed when fractured, these vessels often dilate.
4th. External frictions, if they are not so violent as to embarrass
the venous circulation, evidently facilitate it; this is one of the
advantages of dry frictions. 5th. A slight compress, not sufficient
to check the venous blood, often promotes its circulation, when the
external organs are weakened. We know, since the time of Theden and
Desault, the advantage of tight bandages, for varicose ulcers, even for
varices, &c.
Since the principle of the motion of the venous blood is generally
spread throughout the whole general capillary system, instead of
being concentrated, like that of the arteries, in a single organ, it
is evident, that this motion cannot be uniform, that it must vary
according to the state of the capillary system in the different parts;
that it can be more rapid in some veins, and slower in others. This is
in fact what we see, especially externally where the veins are more
or less swelled, according as the blood circulates there more or less
rapidly. In the arteries on the contrary, the motion is every where the
same; it is a general and sudden shock, an impulse, which, every where
felt at the same time, is necessarily every where uniform; so you never
see some arteries more full, others more empty, as it happens in the
veins.
There are numerous researches to be made on the motion of the blood
in the veins. Notwithstanding all that authors have written upon this
question, there is an obscurity in it in which we perceive but few
rays of light. These difficulties arise from this, that we do not know
precisely what is the kind and form of motion communicated to the blood
in the capillary system, what is the influence of the vascular parietes
upon this fluid, &c. &c. Our knowledge upon this point is reduced to
certain views which I have just presented, and which are particularly
relative to the parallel between the motion of the blood in the veins
and the arteries. I believe that this parallel carried further at some
future day, will throw much light upon the venous circulation; in fact,
as the first motion is much more easily understood than the second,
we must proceed from what is known to what is unknown, and place in
opposition what we are acquainted with in one, with that which we seek
to know in the other. This is the summary of this parallel, though
imperfect; 1st, General pulsation in the arteries, absence of this
general pulsation in the veins. 2d. Rapidity of the course of the blood
in the arteries; slowness of the same course in the veins. 3d. Greater
capacity and thinner parietes in the veins; less capacity and greater
thickness in the parietes of the arteries. 4th. Necessity for accessory
assistance for the venous circulation; the inutility of this assistance
for the arterial circulation. 5th. The blood flowing per saltem, from
the second, the uniform flow from the first. 6th. The susceptibility
of the blood in the veins, to be influenced by its gravity and other
accessory causes; there is some of this influence in the arterial
motion. The following are the phenomena, which, from what we have just
said, evidently depend upon the existence of an agent of impulse at the
origin of the arteries, and of the absence of this agent at that of the
veins.
1st. Constant uniformity of the motion in the arteries; variety
of motion in every part of the venous system; 2d, dilatation and
contraction generally the same in all the arteries of dead bodies;
extreme variety in this respect in the veins of the different parts;
these are the other phenomena which arise from the unity of impulse in
the first, and from the varieties of the principle of the motion of the
blood in the second, &c.
Some authors have insisted much, in explaining the causes of the
difference of the arterial and venous motion, upon this, that in the
arteries the blood is propelled in decreasing vessels, to the capillary
system that resists; in the veins on the contrary it flows in vessels
always increasing till it arrives at the right auricle, which offers
no resistance. But the black abdominal blood is also carried without
the agent of impulse, in a series of decreasing tubes to the capillary
system of the liver, and yet the motion is analogous to that of the
veins.
_Sympathies of the Veins._
The sympathies of the veins are very obscure, like those of the
arteries. As the textures of these two kinds of vessels are rarely
affected, as inflammation and the different kinds of tumours do not
frequently exist in them, and as they are hardly ever the seat of pain,
we know but little of the influence they exert upon the other textures.
However when we transfuse substances into the vessels, we have often
seen acrid and irritating ones upon being introduced into the veins,
produce sudden convulsions in different muscles.
As to the influence that the other organs when affected, exert upon
the veins, we know also but very little. As they are every where
disseminated, like the arteries and the nerves, it is difficult often
to know if it is the vein itself or the organ that it forms, which is
the seat of the sympathetic phenomenon.
ARTICLE FOURTH.
DEVELOPMENT OF THE VASCULAR SYSTEM WITH BLACK BLOOD.
I. _State of this System in the Fœtus._
The veins have in the fœtus an arrangement inverse of that of the
arteries; they are in proportion much less developed. It is not in the
great trunks, as in the venæ cavæ, subclavians, iliacs, &c. that we
should compare these vessels, because the reflux of the blood at the
moment of death often dilates these trunks, so as to make us believe
that they are much larger than they really are in a natural state.
It is in the branches and the ramifications that we should make the
comparison; now it is easy to see there, that the veins nearly equal
the arteries, but are not superior to them, as is uniformly the case in
the adult.
However, the side of the heart with black blood, and the pulmonary
artery which make a part of the system with the veins, are
proportionably larger than these. This arises not only from their
receiving and transmitting the blood of these vessels, but also that
of the umbilical vein. It is to this last circumstance that must be
attributed also an anatomical fact always existing in the fœtus, viz.
that the very short trunk of the vena cava, which is extended from the
liver to the heart, is found in proportion much greater than the trunk
of the superior vena cava, which is not the case in after life.
The less development of the venous system, compared with that of the
arteries, appears to arise in the fœtus from this, that much substance
being employed for nutrition which is very rapid in the early periods,
less returns by the veins. This phenomenon however is not peculiar
to the black blood. We shall see that the excretories transmit less
fluids by the glands, and that the exhalants pour out less upon their
respective surfaces. Much blood enters the general capillary system of
the fœtus; hence why the arteries are very large. There remains in the
organs, much of the substances that it contains, to nourish them; but
little goes out of the general capillary system for secretions, and
exhalations; little returns by the veins.
The more the fœtus advances in age, the more of this blood is carried
in the veins. In the early periods, almost all remains in the organs
to form them. Towards the period of birth, these things approximate to
what they will be in the adult.
In this general phenomenon of the venous system in the fœtus, the
proportions are always preserved between the veins of the different
parts, according to the increase of them. It is thus that most of the
superior parts, the brain in particular, being in the fœtus the seat
of a more active nutrition than the inferior, the veins there are also
more developed.
We can hardly distinguish fibres at this age in the venous parietes,
though they no doubt exist. I have only remarked, that they then
contain much fewer small vessels in proportion than the arteries, whose
trunks are covered with them, as it is easy to see upon the aorta.
Though less dilated than afterwards, the veins appear to be as strongly
organized; their parietes are very resisting; they dilate less easily;
this continues during the whole of youth. It is to this that I
attribute the absence of varices at that age. As on the one hand less
blood circulates in the veins, and on the other they appear to be in
proportion more resisting, it is evident that they must yield less.
II. _State of this System during growth and afterwards._
A remarkable revolution takes place at birth, as we have seen, in the
system of black blood. The right auricle and ventricle receive the
whole of the blood, of which a part until then went immediately to the
right side by the foramen ovale. This difference has not much influence
upon the size of the right auricle and ventricle; differences only
in their form take place, which I shall point out in the Descriptive
Anatomy.
During the first years of life, the veins have a real inferiority as
it respects the arteries. This inferiority continues during the whole
time of growth; of this you may be satisfied by examining the external
veins; they are never as evident, or as much developed in children as
in an adult. Compare the arm of a man with that of a child, and the
difference will be perceptible.
The proportion of the cerebral veins over the others, is gradually
lost as we advance in age, because the brain does not continue to
predominate so much in its nutrition.
At the period of puberty, and towards the end of growth in height, the
veins partake of this general plethora, which seems to manifest itself,
and which is, as we have seen, the source of many diseases.
When the growth in length and thickness is completed, the veins begin
to have a larger diameter; they become more prominent externally;
it appears that more blood constantly passes through them. Make the
muscles of an adult man contract strongly, and you will see all the
veins considerably swelled. The same experiment will not produce a
proportional effect upon a young man; ligatures applied show the same
difference.
III. _State of this System in Old Age._
In the last years of life the veins become much developed compared
to what they are in youth; we can say that in this respect, the two
extreme ages exhibit an inverse arrangement. In considering the
external appearance in the two ages, we may be convinced by the
examination of the superficial veins, of the truth of this assertion.
Let us not think, however, that this greater development supposes an
addition of substance in the venous parietes, as for example, the
increased size of the bones depends upon the super-abundance of the
phosphate of lime. It is a simple dilatation of these parietes, which
are weakened, and become more slender, instead of increasing. This
dilatation is owing to the loss of their elasticity and to the greater
quantity of blood they carry. In fact the motion of decomposition
evidently predominates in old age over that of composition. More
substance is taken from the organs than is added to them, at this
period. I know not but that the bones receive a greater quantity of the
substance that nourishes them. In all the other organs, an opposite
phenomenon is evident; hence their horny hardening, their withering,
if I may use the term. Now, as the system with black blood is that in
which is poured all the residue of the decomposition of the organs, it
is not astonishing that it should be dilated in old age; so the system
with red blood, which carries the materials of their composition,
predominates in the first year of life.
The superabundance of black blood in old age however, is to a certain
degree deceptive; it depends in part upon the slowness of the
circulation in the veins, in which the blood, moved with difficulty on
account of the weakness of the capillary system, tends to stagnate,
and dilate them, as I have said before; so that though there would be
less black blood returning from the organs, there would be more in
the veins, than in the adult; the velocity of the circulation then
would be much less. There takes place in the whole system, what exists
in a varix, for example, in which the blood accumulates because its
velocity is diminished. It is not necessary then to believe, that the
superabundance of the black blood in old age, supposes a plethora
like that of the red blood in infancy, in which, on the one hand, the
arteries contain more fluid, and on the other they propel it with
greater velocity. We know from this that the dilatation of the veins
in old age is a further proof of the principles established above;
viz. that the capacity of the veins is always in an inverse ratio to
the velocity of the fluids that go through them. It admits of but
an inaccurate comparison, though it may give an idea of what passes
in the venous system; a river which is very broad above a bridge,
flows slowly; but its bed being much contracted under the arches, its
velocity is much increased; so that the equilibrium may be established.
So in the veins, there is little velocity and much capacity in old age,
and much velocity and but little capacity in infancy.
Anatomists know very well the difference of the arteries and the veins
at the two extreme ages of life; they choose old subjects to study the
veins; on the contrary, these subjects are wholly improper for arterial
injections, which succeed so well, and sometimes too well, in infants,
in whom every thing appears to become vascular, and in whom the
examination of the veins would be very difficult, and even impossible.
The veins of the inferior parts are generally more dilated in old age
than those of the superior; this arises from the habitual weight of
the column of blood, which constantly acting, produces finally a real
effect; for, as we have said, the venous circulation is much influenced
by mechanical causes, owing to the want of power in the cause that
circulates it; hence why varices are infinitely more frequent in the
inferior than the superior parts, in which they are hardly ever found.
In women who have had many children, we see this dilatation of the
veins of the inferior parts in a very evident manner; very often
there are varices in them. Observe that this disease seems to be the
companion of old age more particularly than that of every other age. On
the contrary, we rarely see aneurisms in old people. The rupture of the
veins has been almost constantly observed at this or the adult age. I
hardly know an example of it in infancy.
The pulmonary artery does not dilate in old age in proportion to the
veins; because, removed from the action of foreign bodies, and provided
at its origin with an agent of impulse formed of a firm and resisting
texture, it has not been in the habit of yielding like them.
IV. _Accidental development of the Veins._
The veins are accidentally developed in two ways. 1st. In cancerous
tumours, in fungi, &c. in which more red blood enters, they acquire
a size in proportion to that of the arteries; now, as they are
superficial, we see more easily their increase than that of the
arteries; this increase, which has been taken for a characteristic
of cancers and other analogous tumours, is only a consequence of the
increase of nutrition. The motion of the blood is as rapid there as in
the other veins; there is no obstruction to it. 2d. There are cases on
the other hand, in which the veins dilate, because the blood cannot
easily circulate in them, and because the velocity of its course is
diminished. For example, the whole venous system of the abdominal
parietes is often increased in ascites; it is not because there is more
blood circulated; there is less than in the ordinary state; but it is
because the venous parietes having in part lost their elasticity, like
the neighbouring parts, the circulation becomes slower; now the slower
it is, the more the blood accumulates and the more the venous parietes
are dilated. It is then a kind of general varix in a division of the
veins. There is not more blood brought by the arteries, as in the
preceding case; the same thing in part happens in old age.
ARTICLE FIFTH.
REMARKS UPON THE PULMONARY ARTERY AND VEINS.
Though in the exposition of the two systems of black and red blood,
I have considered the pulmonary artery as making a part with the
veins, and the pulmonary veins as a continuation of the arteries, yet
their nature is wholly different. There are in truth but two general
membranes, forming the two great tubes in which are contained the two
kinds of blood, which are every where of the same nature, from the
capillary system to the pulmonary. The textures added to the exterior
of these two common membranes are essentially different. Thus the
texture of the pulmonary artery, though added to the membrane with
black blood, is, in point of thickness nearly of the same nature as
that of the aorta and its divisions. So the texture of the pulmonary
veins, though united to the membrane with red blood, is the same as
that of the other veins.
This uniformity in texture supposes an uniformity in the functions,
and this is really the case. The mechanical laws of the circulation of
black blood are the same in the pulmonary artery as those of the red
blood in the aorta. So the laws of the general venous circulation are
the same with those of the pulmonary veins; inspection proves this;
and, moreover, it must be so, since the relation of the heart to the
two kinds of vessels, the veins and the arteries, is the same.
Each system of blood, then, has its two modes of circulation. Sudden
motion, generally communicated, and not the progressive undulation of
the fluid; a pulsation by a real locomotion, a general straightening of
all the divisions of the same trunk at each impulse of the heart; these
are the general mechanical characters of the artery with red blood,
as well as that with black. Absence of pulsation, slowness in the
course of the blood, want of straightening, &c.; these are the general
attributes of the veins of each kind of blood.
There are no doubt general modifications that arise from local causes.
Thus, on account of the short course of the pulmonary veins, the weight
has scarcely any influence upon the blood; they never become varicose;
the motion of the fluid is more rapid in them, since they have less
time to lose that which is communicated to the blood in the pulmonary
capillary system, &c.; thus the artery of the same name, whose branches
are less tortuous, does not seem to me to have pulsations as evident
as those of the aorta, &c. But these general phenomena are always the
same; they are but different modifications.
This is why the general arrangement is nearly the same in the veins and
in the arteries, whether they circulate red blood or black. Thus, for
example, each of the two arteries go off from a ventricle by a single
orifice, necessary for the unity of the impulse of the blood, for the
uniformity of its course in the divisions of its great vessels, and
for the simultaneous pulsations in all the divisions. On the contrary,
the veins pour into the heart the red and black blood by many separate
orifices; this is of no consequence, since, as we have seen, the motion
of this fluid in the veins is not uniform, but may be accelerated or
retarded in a part, by the influences it receives; thus, it may pass
with velocity through the opening of the vena cava superior, and slowly
through that of the vena cava inferior, &c.
From the preceding considerations, it seems, that if we have no
regard but to the mechanism of circulation, that it is almost of no
consequence whether we consider with the ancients the small and great
circulation by studying first the course of the blood in the artery
and the pulmonary veins, then in the aorta and the general venous
system; or of studying, as we have done, the course of the blood, first
in the pulmonary veins and the aorta, then in the general veins and
the pulmonary artery. But if we consider this great function in the
important relations of nutrition, secretions, exhalations, for which
they furnish the materials, of the general stimulus it carries to
all parts, and which is indispensable to the support of life, of the
introduction of foreign fluids in the body of the animal, and of the
change of these fluids into its own substance; then I think it must be
described as I have done it.
ARTICLE SIXTH.
ABDOMINAL VASCULAR SYSTEM WITH BLACK BLOOD.
_Situation, Forms, General Arrangement, Anastomoses, &c._
There is in the abdomen a system of black blood wholly independent
of the preceding, arranged precisely like it, with the difference,
that its course is shorter, and that it has no agent of impulse. This
system, usually known by the name of Vena Porta, is found in most
animals.
It arises from that part of the general capillary system which
belongs to the intestines, the stomach, the omentum, the spleen, the
pancreas, &c. and generally to all the abdominal viscera connected
with digestion. This origin is remarkable. The viscera in the abdomen,
foreign to the phenomena of digestion, are also foreign to the origin
of this system. The kidnies and their dependancies, as the glandulæ
renales, the ureters, the bladder, the urethra, &c. the genital organs,
the diaphragm, &c. the abdominal parietes themselves, &c. &c. pour
their black blood into the preceding system. Why are the digestive
viscera, in their whole extent, different from the others, in the
destination of their black blood? To answer this question, we must know
the uses of the system of which we are treating; now, of these we are
ignorant.
Thus rising from the whole gastric apparatus, this system forms into
two or three trunks, which soon unite into a single one, which occupies
the superior and right part of the abdomen below the liver.
This common trunk soon divides again into many branches, which spread
in the liver into an infinity of ramifications, and are spent upon the
texture of that organ.
This system, then, presents the same general arrangement as the
preceding; it is composed of two trees united by their lopped summits,
that intermix with each other. Place an agent of impulse at these
summits, the arrangement will be the same as in the two preceding. The
blood is moved from one capillary system to another. Divided at first
into small streams, it is formed into masses constantly increasing to a
certain point, then it is divided again, and is carried in streams not
larger than the first.
In the abdominal portion, the ramifications, the small branches, the
branches and the trunks are arranged very nearly as in the general
venous system. The ramifications are found in the organs, the small
branches in their interstices, most of the branches are situated in the
layers of the peritoneum, there accompanying the arteries, and the
trunks wind along the subjacent cellular texture. As to the hepatic
portion, contained wholly in the liver, it is divided there nearly like
the preceding.
The anastomoses present the following arrangement in the system of
which we are treating. 1st. Its hepatic portion appears to want them;
all the branches, smaller branches, and ramifications, go separately.
As the circulation is not subject in the liver to increase or
diminution, the solid texture of this organ protecting the vessels,
the blood has no occasion for the means by which it can deviate from
one place to another. Thus the great divisions of the pulmonary artery
and veins, which go immediately into the lungs where they are wholly
distributed, do not communicate with each other. Thus the branches of
all the arteries and of all the veins contained in the interior of a
viscus, as in the kidney, the spleen, &c. are most commonly without
communication. 2d. As to the abdominal tree, its anastomoses are very
frequent in the smaller branches. We see all along the small intestines
arches exactly like those of the mesenteric arteries; less frequent in
the great intestines, they are, however, very evident in them, as upon
the stomach; in the branches and the trunks they do not exist.
The anastomoses in the system of black abdominal blood are necessary
there from the frequent delays that this fluid may experience. For
observe, that the circulation is performed for the abdominal portion
according to the same laws as in the other veins, and that consequently
that the force that can circulate the blood there, can yield to the
least effort. Now in the different motions of the small intestines,
often too great a fold, the pressure of these organs filled with
aliments upon the veins, when we are lying on the back or the side,
and which pressure the veins support only by their resistance, and a
thousand other causes, impede the course of the blood in one branch,
and force it to flow by anastomoses into others. Observe also, that an
obstacle which is of no consequence to the red blood, on account of the
very strong impetus that is given to it, is very important to the two
circulations of black blood, which receive but a feeble impulse.
The influence of gravity is evident in the blood of this system, as
in that of the preceding. Thus you see the hemorrhoidal veins, more
exposed than all the others to this influence by their position, become
much more frequently varicose; and it is even rare to find dilatations
in the superior mesenteric veins, splenic, gastro-epiploic, &c. &c.
whilst there is no part in which they exist more often than in the
hemorrhoidal. Thus we have seen the preceding system dilated rarely
above, but very frequently below.
The system with black abdominal blood communicates but very little with
the general system; if there are anastomoses, it is only in the last
divisions; do these anastomoses exist? I believe we may consider these
two systems as independent of each other.
_Organization, Properties, &c._
Many authors, Haller in particular, considering that the system of
which we are treating is destitute of an agent of impulse, have
admitted in them a force of structure superior to that of the other
veins; but after examining it attentively, I am convinced that it is
precisely the same. The cellular covering, of a peculiar nature, which
surrounds it, and which is analogous to that of the other vessels, is
only a little more evident; this makes these veins at first appear
thicker; but by raising this covering we see that the internal membrane
is of the same nature, only perhaps a little less extensible. We do not
discover the venous longitudinal fibres so well as in the preceding
system; I doubt even if they exist in the trunks, in which we should
be able to see them better.
The two portions of this system, the hepatic and abdominal, appear to
be completely uniform in their structure. Only the first is every where
accompanied by a kind of membrane, which appears to be cellular, but
whose nature is not yet well known, and which is called the capsule of
Glisson. This capsule, intimately connected with the substance of the
liver, adheres more loosely to the veins; so that when they are empty,
there is often a space between them and it; it is this that makes them
fold up when we cut the liver in slices. I think that we are entirely
ignorant of the object of this anatomical arrangement.
The analogy between the systems with black blood, the abdominal and
general, supposes them the same in properties, sympathies, affections,
&c. I have often irritated the mesenteric veins, upon which it is
extremely easy to act, by drawing through a small wound of the abdomen
a portion of the intestinal canal; the results have always been the
same as in the preceding system. Only when we inject air, the animal
does not struggle, does not appear to suffer, and the experiment is not
fatal; this proves still more, that it is not by its contact upon the
veins or the heart, that the air is injurious, but by its action on the
brain.
The common membrane of the system of which we are treating, is
distinguished from that of the preceding, in this, that it is wholly
destitute of valves. This appears to be owing to two causes, 1st, to
this, that the course of the blood being shorter, it has less need of
being supported; and 2d, to this, that the middle part of this system,
wanting an agent of impulse, there is no reflux as in the preceding
system. In fact, at every contraction, the right auricle sends, as
I have said, a portion of its blood into the veins, which resist by
the valves. Here, on the contrary, the course of the fluid is always
uniform from one capillary system to the other; there is no cause of
retrograde motion.
_Remarks upon the motion of the Black Abdominal Blood._
This uniformity in the course of the motion of this black blood, is
not merely the result of the absence of the agent of impulse, but also
of this, that the liver does not present as many obstacles to it, as
the lungs do to the preceding black blood. Observe also that the liver
occupies in regard to this system, the same place as the lungs in
regard to the other; it is the termination of the circulation of which
we are treating. Having no dilatation or contraction, deprived of the
fluid which acts incessantly upon the lungs, and which, loaded with
different foreign substances, can often alter the vital forces of these
organs, so as to interrupt the passage of the blood, &c. The liver,
having a solid and granulated substance, in which no extraordinary
motion can take place, except those of the general locomotion of the
organ, is evidently incapable of frequently interrupting the course
of the black blood, which the abdominal system sends there. Add to
this the want of the agent of impulse, and you will understand, 1st.
why, when the abdomen is open, we never see a pulsation, a reflux
in the veins of the abdominal system, as we observe in those of the
other system; 2d. why we always find there nearly the same quantity
of blood; 3d. why, consequently, we do not discover, either in the
common trunk that corresponds to the heart, or in its branches, the
numberless varieties of dilatation and contraction, which the right
side of the heart, and all the great venous trunks so frequently
exhibit, so that scarcely two subjects are alike in this respect,
whilst here the arrangement is always nearly the same; 4th. why the
liver is not subject to the innumerable varieties in size that the
lungs are. This deserves a particular consideration. You will rarely
find the lungs twice containing the same quantity of blood; the weight
varies enormously in this respect. Now this arises from the greater or
less obstacles the blood has met with in passing through these organs
in the last moments of life. We can make them more or less heavy in
an animal, by making him die of asphyxia or hemorrhage, consequently
by filling with blood, or emptying the extremities of the pulmonary
artery. Whatever on the contrary is the kind of death, the hepatic
extremities of the abdominal system, contain always nearly the same
quantity of blood; suppose, that more remains than usual in this system
at the moment of death, it is generally distributed, because there is
no agent of impulse, which, at the last moments, drives the greatest
quantity to the liver, as happens to the lungs. We understand from
this, why the liver exhibits a firm, resisting texture, not extensible
like that of the lungs. Sometimes the blood enters it in greater or
less quantity, it is even, more or less heavy according to the kind
of death. But these varieties belong only to the hepatic veins, which
enter into the vena cave inferior just below the heart; they arise from
the greater or less reflux of blood that takes place there, as in all
the great venous trunks; they consequently arise almost always from the
lungs; so that when we see that they are loaded with blood, the right
auricle consequently distended, we may also be sure that the liver
contains more of this fluid than usual. But this phenomenon, of which I
shall speak when treating of the liver, is wholly disconnected with the
system which I am describing.
The mechanism of the circulation of the abdominal part of this system,
is precisely the same as that of the veins. As to that of the hepatic
part, it is unlike that of any other part of the economy. It has no
analogy to that of the arteries, for in them the heart is almost every
thing, and here there is nothing to correspond to that system; for
certainly there is no kind of contraction in the common trunk of the
two trees, as I have been frequently convinced. It is then the same
motion, which is continued from the gastric viscera to the liver. There
is still much obscurity to be removed concerning this motion, as well
as the preceding. Every judicious mind perceives that there is a great
void, in reading what has been written upon the motion of the general
venous blood, and upon this.
We cannot deny but that external agents do much in this last
circulation as in the first. The uniform elevation and depression of
the diaphragm, the corresponding motion of the abdominal parietes,
the alternate dilatation and contraction of the hollow viscera of the
abdomen, the constant locomotion of the small intestines, &c. all
these causes certainly have an influence upon the motion of the black
abdominal blood; and I even think, that the absence of most of them
contributes to retard this motion in the hemorrhoidal veins, and to
occasion varices in them.
This influence is not however such as Boerhaave thought, that the
circulation could not go on without it. In fact, when the abdomen of
an animal is opened, the blood is transmitted the same to the liver,
and spouts in the same manner from an open vessel; but we observe
a sensible weakness in a short time, and this before the general
circulation is enfeebled.
_Remarks upon the Liver._
The use of the liver, in being the termination of the black abdominal
blood, as the lungs are that of the black blood of all the rest of
the body, gives it an importance unknown to all the other secretory
organs. Some authors, in observing the enormous size of this viscus
compared to the quantity of fluid secreted by it, have suspected that
it had another use, besides the secretion of this fluid. This suspicion
appears to me, to amount almost to certainty. Compare the hepatic
excretories and reservoirs, with the same parts in the kidnies, the
salivary glands, the pancreas even, and you will see that they hardly
surpass them, and that they are inferior to those of the first. Then
compare the size of the liver with that of the kidnies, of the salivary
glands, &c. and you will see the difference. If on the other hand, we
examine the bile, voided with the stools which it colours, if we open
the intestines at the different periods of digestion, as I have done,
to see the quantity of this fluid that is poured out; if we keep an
animal without food in order to let it accumulate by itself in the
intestines; if we tie the ductus choledochus to retain the bile, &c. it
is impossible not to be convinced, that the quantity of this fluid is
disproportioned to the size of the liver. This viscus is alone equal in
size to all the other glands united; now, place on one side, the bile,
and on the other, all the secreted fluids, the urine, the saliva, the
pancreatic juice, the mucous juices; &c. you will see how enormous the
difference is.
Since then the secretion of bile is not the only object of the liver,
it must have some other use in the economy. What this is we are
ignorant; it is however undoubtedly connected with the existence of
the system with black blood of which it is the termination, and is
especially relative to this system. The following considerations appear
to prove that this use is among the most important.
1st. The liver exists in all classes of animals. In those even in
which most of the other essential viscera are very imperfect, it is
well developed. 2d. Most of the passions affect it particularly, many
of them have an exclusive effect upon it, whilst a great number of
the other glands hardly perceive them at all. 3d. In diseases, it
takes as evident a part as the first viscera in the economy. In many
nervous affections, in hypochondria, melancholy, &c. it has a great
influence compared to other glands. We know how easily its functions
are deranged. It has undoubtedly no connexion with some affections
called bilious, and which are seated exclusively in the stomach, but
it certainly has a part in most of them. Since there is no doubt that
the jaundice depends wholly upon a serious affection of this viscus,
we ought certainly to conclude that the yellow tinge of the face in
many of these affections, arises from a cause existing in this viscus,
and which is not sufficiently powerful to produce jaundice. Whether
in order to produce this tinge, the bile circulates or not with the
blood, is of no consequence; it is incontestible that it is occasioned
by affections of the liver; now the numerous cases in which it takes
place, prove how much this viscus is often affected; there is certainly
no gland in the animal economy so frequently. 4th. Shall I speak of
organic affections? compare in the examination of bodies, those of the
liver, with those of all the other organs of the same class, and you
will see that there is no one equal to it in this respect; the kidney
approaches it, in the frequency of the alteration of its texture, but
it is far from being equal to it. 5th. Who does not know the influence
of the liver upon temperaments? Who does not know that its predominance
gives to the external appearance, the functions, the passions, the
character even, a peculiar shade which the ancients have noticed, and
which modern observations have confirmed? Now see if the other glands
have a similar influence in the economy. 6th. The liver is, with the
heart and the brain, the organ that is first formed; it precedes all
the other organs in its development; it is incomparably superior, in
this respect, to all the glands.
From all these considerations, and from many others that I might
add, we may conclude, I think, that the unknown part which the liver
performs in the animal economy, besides the secretion of bile, is among
the most important. The study of this part, is one of the points most
worthy of arresting the attention of physiologists.
It has been said latterly, that the liver corresponded to the lungs in
their functions of removing from the blood its hydrogen and carbon. I
know not how this fact can be proved by experiment; but I am positive
that the liver does not turn the black blood of the abdominal system
into red. 1st. The blood of the right auricle is of the same colour
as that of the vena cava inferior; now if the blood went red from the
hepatic veins, it would certainly give a brighter tinge to that of the
auricle. 2d. Having opened the abdomen and thorax of a dog, I tied with
a curved needle the vena cava at its entrance into the heart and above
the kidney, then by detaching the liver from behind, I cut the portion
intercepted between the two ligatures, and where the hepatic veins
opened; the blood came out as black as that of the rest of the system.
3d. Tear out the liver of a living animal, examine immediately its
veins, you will see that they contain a blood analogous to that of the
others. 4th. This viscus, cut in slices in a living animal, pours out
behind an analogous fluid, except some small red streams furnished by
the last small branches of the hepatic artery; this is wholly different
in the same experiment made upon the lungs.
If the black abdominal blood receives any modifications of its nature
in the liver, they certainly have no influence upon its colour, its
consistence, or sensible qualities.
The general opinion is that the black abdominal blood serves for
the secretion of bile, and that the hepatic artery is only destined
to nourish the liver; this is what Haller has adopted; I have also
admitted it; but I am far from considering it as clearly demonstrated
as it has generally been thought to be; the following observations
prove, that we ought to consider it as an hypothesis somewhat uncertain.
1st. It is said that the hepatic blood, blacker, more oily, impregnated
with the vapours of the excrements, of a bitter taste even, approaches
nearer the nature of bile than the arterial blood, and that it is
consequently more proper to form it. I do not know whether this
blood has been analyzed comparatively; but I have certainly not
found any difference in its external attributes; I did think that
in an experiment I observed fatty drops swimming in it; different
experiments have convinced me that it was an error. I doubt whether
it could ever be demonstrated that the alkaline particles of aliments
and of excrements pass into the vena porta; this passage is a
gratuitous supposition. 2d. It is said that the volume of the liver is
considerable compared to the hepatic artery; this is true; but it is
not with the size of this viscus that we should compare that of this
artery, to know if it furnishes the materials of secretion, since we
have seen that it is impossible that the whole substance of the liver
should be destined to secrete bile; it is with the biliary ducts and
their reservoir, that we should make the comparison; now this artery
is exactly proportioned to these ducts; there is between them nearly
the same relation as between the renal artery and the ureter; on the
contrary, the biliary ducts are manifestly disproportioned to the vena
porta. 3d. It is said that the slow motion in this vein, is favourable
to the secretion of bile. But upon what positive data is this assertion
founded? Why is slowness of motion more necessary for this secretion
than for others? 4th. It is said that the hepatic artery having been
tied, the secretion of bile continued. But when we know the relation
of parts, the least reflection is sufficient to convince us, that a
ligature of this kind cannot be made without producing a derangement
that will prevent us from distinguishing any thing. I attempted it
once, but could not finish it; I was almost persuaded of it before.
5th. It is said that the black blood is more proper to furnish the
materials of the bile than the red. But what is the reason of it? is
it because this blood contains more carbon and hydrogen? But it is
then the black blood that furnishes the fat also; now all anatomists
are agreed, that it is exhaled from the exhalant extremities of the
arteries; the same is true of the marrow, the wax, and in general of
all the oily fluids. 6th. A fine injection, made in the hepatic portion
of the abdominal system with black blood, passes into the biliary
vessels. But a similar passage takes place in an injection from the
hepatic artery. 7th. It is said that the black abdominal blood in the
spleen has qualities essential to the bile. But the secretion of this
fluid can evidently take place without the spleen; many experiments
prove this. 8th. It is said that at the instant the vena porta is tied,
bile ceases to be secreted; it is undoubtedly less difficult to tie
the trunk of this vein below the duodenum than the hepatic artery. How
can we examine what is going on in the liver? Do we judge by the fluid
flowing from the hepatic duct? But open the duodenum, and you will
not very often see the bile running out at the opening of the ductus
choledochus, undoubtedly because the air contracts and irritates this
duct. This phenomenon, observed after a ligature is applied, is not
then conclusive; moreover there does flow towards the time of digestion
but too little bile by the ductus choledochus, to be able to estimate
it. In fine, what inference can be drawn from an animal whose abdomen
is open?
These different reflections prove, I think, that we have not
sufficiently direct proofs, to decide whether the secretion of bile
is from the abdominal black blood or the red. I do not attribute this
function more to one than the other; I say that these things should be
subjected to a new examination, and that this example is a proof that
the opinions most generally received in physiology, those consecrated
by the assent of all celebrated authors, often rest upon very uncertain
foundations. We are yet far from the time when this science will be
only a series of facts rigorously deduced from each other.
The hepatic artery has been said to resemble the bronchial, and the
hepatic vena porta the pulmonary artery; this is true in the general
arrangement; but what is the proof of it as it regards the functions?
On the contrary, I have proved above that those of the two last
vessels are not similar. Let us wait, before deciding, for further
and positive researches; let us doubt till then; let us not attribute
the secretion of bile to the hepatic artery, nor the vena porta, nor
to them unitedly. Certainly it is by one of these three means; but
which? what vessel furnishes the secretion of bile? what part does the
black abdominal blood perform in the liver, if it is not from it that
this fluid is secreted? what, in fine, is the function of the hepatic
artery, if it is not connected with this secretion? These are questions
to be resolved.
Physicians have also hazarded opinions upon the influence of the
black abdominal blood in diseases. Undoubtedly the expression, _vena
portarum, porta malorum_, contains a very true meaning; but certainly
in the present state of our knowledge, it is, in a strict sense, only a
play upon words. If we would express by it the frequency of affections
of the liver, it is without doubt just; but if it is employed to
express the influence of the vena porta in diseases, it is vague and
does not rest upon any positive fact. The more we open dead bodies, the
more we shall be convinced, I think, of the necessity of a precise and
accurate language, freed from all these ingenious, hypothetical ideas,
which do honour, it is true, to their author, but which retard science,
by introducing into it a manner of seeing hypothetically, and contrary
to the spirit of observation.
_Remarks upon the course of the Bile._
Though this question may be to a certain degree foreign to my object,
yet as the black abdominal blood has perhaps a real influence upon the
secretion of the bile, as my experiments upon this point determine
with precision the course of this fluid, I do not think it useless to
relate them here. All that is known further upon the uses, mechanism,
&c. of this secretion is to be found in works of physiology, to which I
refer.
There has been much discussion to ascertain if there was cystic and
hepatic bile, if one was of a different nature from the other, if their
quantity increased or varied, &c. Contrary and even opposite opinions
have been supported by numerous experiments made upon living animals,
as Haller has observed. These experiments, though at first view
contradictory, are not so, however, as I was convinced by repeating
them at different periods of digestion and during the abstinence of the
animal; it had not been done with precision. The following is what I
have observed in dogs, which I have used in my experiments.
1st. During abstinence, the stomach and small intestines being empty,
we find the bile in the ductus hepaticus and ductus choledochus
yellowish and clear; the surface of the duodenum and jejunum tinged by
bile which has the same appearance; the gall-bladder much distended by
a greenish, bitter bile, much deeper coloured and more abundant if the
abstinence has been long. 2d. During digestion in the stomach, which
may be prolonged for a length of time, by giving to a dog large pieces
of meat, which he swallows without masticating, things are nearly in
the same state. 3d. At the beginning of the intestinal digestion, we
find the bile of the hepatic duct always yellowish, that of the ductus
choledochus deeper coloured, the gall-bladder less full and its bile
already becoming clearer. 4th. At the end of digestion and immediately
after, the bile of the hepatic duct, of the ductus choledochus, that
in the gall-bladder, and that which is found upon the duodenum, are
of precisely the same colour as the common hepatic bile, that is, of
a clear yellow, and a little bitter. The gall-bladder is about half
full; it is flaccid, not contracted.
These observations, repeated a great number of times, evidently prove
that this, during abstinence and digestion, is the manner in which the
flow of bile takes place; 1st, it appears that at all times the liver
secretes a certain quantity, which is increased during digestion;
2d, that which is furnished during abstinence is divided between the
intestine that is always coloured with it, and the gall-bladder which
retains it, without pouring out any portion of it by the cystic duct,
and in which, thus retained, it acquires an acrid character and a deep
colour, necessary, no doubt, to digestion which is to follow. 3d.
When the aliments, having been digested by the stomach, pass into the
duodenum, then all the hepatic bile, which was before divided, flows
into the intestine, and even in greater abundance. On the other hand,
the gall-bladder pours also that which it contains upon the alimentary
mass, which is then completely penetrated with it. 4th. After
intestinal digestion, the hepatic bile diminishes, and a part begins to
flow into the duodenum, and a part to flow back into the gall-bladder,
in which, if then examined, it is found clear and in small quantity,
because it has had neither time to be coloured or accumulate.
There is then this difference between the two biles, that the hepatic
flows almost in a continued manner into the intestine, and that the
cystic flows back, except during digestion, into the gall-bladder, and
flows, during this function, towards the duodenum; or rather it is the
same fluid, of which a part always preserves the same character that
it had at its exit from the liver, and the other assumes a different
one in the gall-bladder. The diversity of colour in the cystic bile,
according as it has been retained long or not, has much analogy to the
colour of the urine, which is found more or less deep coloured, as it
has been for a longer or shorter time in the bladder.
As to the course of the bile in relation to the stomach, I believe
that this viscus contains a certain quantity of it at all times. When
empty, we find there a mixture of gastric juices and mucus more or
less abundant, sometimes mixed with small bubbles of hydrogen, which
burn when brought in contact with flame, and almost always tinged
with a yellowish colour from the bile that has flowed up through the
pylorus. Haller says that this reflux of bile into the stomach does not
always happen; Morgagni says that it always does in men. I have never
opened a dog, in whom it has not been seen when the stomach was empty,
especially if it had been so for some time. Human dead bodies are not
proper to decide this question, because the kind of disease alters
almost inevitably the course, the nature, and even the colour of the
bile. I shall say in another volume what conclusion we should draw from
this, as it respects bilious vomitings.
In a state of fulness, it has sometimes appeared to me impossible
to estimate the reflux of the bile; in other states, between the
alimentary mass and the parietes of the stomach, I have seen yellowish,
gastric fluids; but this mass itself never has this colour.
The bile that flows into the stomach has always appeared to me to be
hepatic bile, from its light colour. I think that I have opened a
sufficient number of living animals to convince me, that this bile is
hardly ever found very green, and that it acquires this colour from the
gall-bladder; and that it is this that is brought up by vomiting in
some affections. The reflux of this bile appears to be an effect of the
affection itself. This observation agrees with that made above, viz.
that the hepatic bile alone flows into the duodenum in abstinence. It
alone can then, as we may be convinced, flow into the stomach. During
intestinal digestion, in which the cystic bile flows, it is evident,
that the aliments going continually out of the pylorus, prevent it from
passing there and entering the stomach; that which we find during
fulness, was there then, or entered there before the peristaltic motion
had begun to evacuate this organ.
When we open the gall-bladder in a dead body, we see that the bile
there exhibits, according to its diseases, a variety of shades of
colour, from that which is black as ink to a kind of transparent
fluid. Ought we then to be astonished, if the vomitings in which the
cystic bile is brought up, that has flowed into the stomach against
the ordinary course of things, should contain matters of such various
colours?
_Development._
In the fœtus, the system of black abdominal blood is not insulated; it
becomes a part of the two others, by means of the ductus venosus. There
is then truly but one vascular system in the fœtus, whilst after birth,
there are three separate ones, two with black blood and one with red.
In the fœtus, it is especially with the umbilical vein that the
abdominal system with black blood is continued. The liver is a centre,
in which both arrive from two different sides, and in which they unite,
in a common trunk. The two columns of blood that they circulate, do not
meet directly; their course forms a very remarkable angle.
When we examine attentively the orifice of the ductus venosus in the
trunk, made by the union of these two veins, we see that it presents
itself naturally to the blood of the umbilical vein; that that of the
vena porta, on the contrary, cannot enter there. In fact, there is a
little fold in the form of a valve, less evident, it is true, than
many others, but yet existing. This fold is only a kind of projection,
placed between the end of the vena porta and the ductus venosus, and
which contracts the orifice of this, so that it is evidently narrower
than the caliber of its own canal. The blood coming from the vena
porta and passing at the side of this fold, presses it against the
orifice, and thus forms an obstacle; that coming from the umbilical
vein, falling, on the contrary, perpendicularly on this orifice,
removes this fold, and enters the canal.
It hence follows that the ductus venosus is evidently destined to carry
to the vena cava the residue of the blood of the umbilical vein; I say
the residue; in fact, as this vein is very large and the ductus small
in proportion to it, it is evident that the greatest part of the blood
penetrates the liver, by the different ramifications that enter its
substance.
The abdominal vascular system is less developed in the fœtus than
afterwards; it consequently carries less blood to the liver; this is
the same arrangement as in all the other veins. I would observe, that
the small quantity, however, which the liver receives in this way, is
more than compensated by that of the umbilical vein. This viscus is,
then, habitually entered in the fœtus, by a greater quantity of fluid
than at any of the other ages. Hence, 1st, why its nutrition is so
developed and its size so great; 2d, why it is, in proportion to its
size, heavier than in the after ages; 3d, why when we cut it in slices,
there flows out a greater quantity of blood; 4th, why, when we dry
slices of the liver of a fœtus, of the same thickness as others taken
from the liver of an adult, and especially of an old person, they are
reduced to a less size.
The disproportion of the size of the liver of the fœtus is more
evident, the sooner it is examined after conception; this is the
same as with the brain. As the fœtus advances towards birth, the
liver approximates in its proportions to the other organs, that which
it will have in the adult. From the observations of Portal, it is
especially till the seventh month, that the liver is predominant. This
circumstance appears to arise from this, that the umbilical vein
transmits as much more blood in proportion to the fœtus, as it is less
advanced in age.
At this age, the blood of the umbilical vein and that of the vena
porta evidently mix, at least in a great measure, in the common trunk.
Is their nature analogous? There is no experimental knowledge upon
this point. But Baudelocque has many times observed that that of the
umbilical vein is redder, and even approximates the nature of arterial
blood. I have not accurately observed this fact in any animals except
guinea pigs, in whom the want of transparency in the cord does not
allow us to see a great difference in the blood of the arteries and of
the umbilical vein; but this difference can be in fact more evident
in man; now, in this case, the umbilical blood appears to lose this
redness in the liver, for very certainly it is uniform beyond this
viscus in the circulation of the fœtus, as I have often ascertained.
At the period of birth, the blood ceasing to come by the umbilical
vein, the liver becomes only the termination of the black abdominal
blood. Then a kind of revolution takes place in this viscus. The
different tubes that carried to it umbilical blood do not close up, but
they transmit exclusively that of the vena porta, which increases a
little in size, because digestion, which begins in the gastric organs,
calls to them more arterial blood, and consequently more is returned by
the veins. This slight increase does not compensate for the absence of
the umbilical blood; thus the liver diminishes proportionally in size
in an evident manner.
As to the ductus venosus, it is obliterated by the effect of the
contractility of texture. The blood coming in the vena porta, has not,
as I have said, any tendency to pass through it, because this canal is
not in its direction; it passes rather into the hepatic vessels, and
the circulation of the liver is established then, as it will always
continue to be.
This then is the difference that birth brings to the hepatic
circulation; 1st, less blood and only one kind entering the liver; 2d,
an interruption of all communication between the general and abdominal
black blood; 3d, proportional diminution of the size of the liver.
Hence there is an inverse phenomenon for this organ and for the lungs.
The latter increases, the other diminishes in activity and size.
The great quantity of blood that enters the liver before birth, and the
size of this organ, compared to the small quantity of bile that escapes
from it, are an evident proof then that it is destined for other uses
besides the secretion of this fluid. There cannot be a doubt upon this
point; it is a proof moreover, that in the adult the disproportion
of the organ to the fluid, though less sensible, supposes also in it
another important function of which we are ignorant.
There ought to be a precise relation between the obliteration of the
ductus venosus, of the foramen ovale and the ductus arteriosus, between
the increased activity of the lungs and the diminished activity of the
liver at birth, &c. We judge of this relation, without knowing it,
because a veil is still spread over the circulation of the fœtus. I
would only observe that the predominance of the liver before birth,
does not suppose any in the system of black abdominal blood; it arises
exclusively from the umbilical vein; thus the proportional volume of
this organ is constantly diminishing afterwards, especially on the
left side, where this vein is distributed, as Portal has observed. It
is difficult to name the period, at which the equilibrium is generally
established.
In youth, the abdominal system of black blood, like the general, is
weak. It is towards the thirtieth or fortieth year, that it seems to
be in its greatest activity; this is the age of gastric diseases, of
hemorrhoids, and of melancholy, which is connected with the state of
the liver.
In old age, the dilatation of the system of black abdominal blood is
much less sensible than that of the preceding system; its vessels
have nearly the same caliber as in the adult age; which supposes a
less diminution in the velocity of the course of its blood, from the
principles established above. It never becomes the seat of any kind
of osseous incrustation, a phenomenon that evidently assimilates
its common membrane to that of the veins, and distinguishes it in a
peculiar manner from that of the arteries.
END OF VOL. I.
* * * * *
Transcriber's Notes
Obvious typographical errors have been silently corrected. Variations
in hyphenation, spelling and punctuation remains unchanged.
Italics are represented thus _italic_.
The large TABLE OF PHYSIOLOGY used curved braces to indicate groups.
For clarity these have been replaced by rectangular braces. In
addition, to fit within page width considerations, the first column of
these tables has been transposed into individual table section headings.