OF THE INFLUENCE OF THE DEATH OF THE LUNGS OVER THAT OF THE HEART.
We have already said, that the functions of the lungs are of two
kinds, mechanical and chemical. Now the activity of this organ
ceases sometimes by the former, and sometimes by the latter of
these functions.
Any wound, which exposes the lungs on both sides, for a
considerable extent, occasions their sudden collapse; any division
of the spinal marrow, which suddenly paralyses the intercostals,
and the diaphragm; any very strong compression exerted at the same
time upon the whole of the thorax, and the parietes of the abdomen,
any sudden injection of a large quantity of fluid into this cavity,
are all of them causes which begin the death of the lungs, by
putting an end to their mechanical functions. Those which influence
in the first place their chemical functions, are the different
sorts of asphyxia, strangulation, submersion, and a vacuum, in
whatever manner produced.
I. _In what manner is the death of the heart occasioned by the
interruption of the mechanical functions of the lungs?_
The interruption of the functions of the heart, can only succeed
in two ways to that of the mechanical functions of the lungs: 1st.
Directly, because a mechanical impediment is put to the circulation
of the blood, by a state of collapse in the lungs. 2dly.
Indirectly, because in such state the lungs no longer receive the
materials, upon which their chemical functions are exerted, and
therefore cannot transmit them to the heart.
Physiologists have all of them admitted the first mode of
interruption, in the Pulmonary circulation. Reflected on
themselves, the vessels of the lungs have not appeared to them, to
be capable of transmitting the blood, on account of the numerous
angles which they make. This idea they have borrowed from the
phenomena of hydraulics, and it is their reason for the death which
ensues, in consequence of a too long continued expiration.
Notwithstanding all which, it has been proved by Goodwyn, that
in such case there remains a sufficient quantity of air in the
air vessels, for dilating them enough to allow of the mechanical
passage of the blood; he proves in consequence, that an unnatural
permanence of the state, in which the lungs are placed from the
act of expiration, does not affect the blood in the way, which is
commonly believed. This is one step towards the truth, but we shall
approach it much more nearly, and even attain it, should we be able
to prove, not only that there remains a sufficiency of air in the
lungs to permit the transmission of the blood, but that the very
folds produced in the vessels by a state of collapse in the organ
are not a real impediment to its course. The following observations
and experiments will assuredly determine this fact.
1st.--I have already proved, that a state of fulness or emptiness
in the stomach, and in all the hollow organs in general, produces
no apparent change in the state of their circulation; and that
the blood in consequence, will traverse the vessels, when bent or
doubled upon themselves, as easily, as when they are distended in
every direction. For what reason should a different effect be
produced in the lungs, by the same disposition of the parts?
2dly.--There are different vessels in the œconomy which we may
alternately bend or extend at pleasure: such are those of the
mesentery, when exposed by an incision into the abdomen of the
animal. Now in this experiment, which has been already made to
prove the influence of the tortuous direction of the arteries
upon the mechanism of their pulsation, if one of the mesenteries
be opened, and then either bent or extended, in either case the
blood will be thrown out with the same degree of violence, and in
equal times will be emitted in equal quantities. I have always
obtained the same result in this experiment which I have many times
repeated. From analogy we might expect the same from the vessels of
the lungs;[79] and from the following experiment it may be proved.
3dly.--Take a dog, cut the trachea, and adapt the tube of an
injecting syringe to it, then make a vacuum in the lungs, and cut
the carotid artery. It is evident, that according to the common
belief, the circulation should be immediately suspended, in this
experiment, since the pulmonary vessels from their ordinary state
of distension, must have passed to the greatest possible degree
of collapse, in consequence of the total abstraction of air;
notwithstanding which the blood will be violently thrown out from
the divided arteries for a certain time, and must consequently
traverse the lungs: it will afterwards cease by degrees, but this,
from causes which I shall explain hereafter.
4thly.--The same effect may be produced by opening, on both sides,
the breast of a living animal, because the warm and rarified air of
the lungs, will be more than balanced by the pressure of the colder
air without;[80] now, neither in this case does the circulation
experience any sudden change. For the sake of greater exactness,
the little air remaining in the cells of the organ may be voided
by a syringe.
Along with these observations let us place the facility with which
the pulmonary circulation continues to be made, when collections of
water, pus, or blood, are lying within the pleura, or pericardium.
In these cases the air vessels are often prodigiously contracted,
and consequently the vessels of their parietes doubled and
bent.[81] If this state be taken into consideration, we shall have
sufficient data for concluding that the tortuous disposition of the
vessels, can never be an obstacle to the passage of the blood; and
therefore, that the interruption of the mechanical functions of the
lungs, can never directly put a stop to the action of the heart,
though it may do so indirectly, in impeding the exercise of the
chemical functions of the lungs.
If then we can determine why the heart remains inactive, when the
latter phenomena are annihilated, we shall have resolved a double
question.
Many authors have asserted that the death, which ensues after a too
long continued inspiration, is owing to the mechanical distension
of the pulmonary vessels by the rarified air, a distension impeding
the circulation. But this reason also is as false a one, as that
which we have already disproved. Inflate the lungs as powerfully as
may be, then tie the trachea and open the carotids, and the blood
will flow as impetuously as when the respiration was perfectly
free.[82]
II. _Why does the heart cease to act, when the chemical functions
of the lungs are interrupted?_
According to Goodwyn, the reason why the contractions of the heart
are stopped, when the chemical functions of the lungs have ceased
to be performed, consists in the want of that excitement which the
red blood only can produce upon the red-blooded ventricle. This
ventricle, says he, has not a sufficient stimulus in the black
blood, and death is occasioned because it no longer is capable of
transmitting any thing to the different organs. In this case death
must happen, as it would from ligature of the aorta--precisely in
the same way as when its source is exclusively in the heart. The
other parts die only for want of blood, just as when in a machine,
the principal spring being taken away, the others cease to act,
because they are not put into action.
On the contrary, I am persuaded that there is a general affection
of all the parts, whenever the chemical functions of the lungs
are suspended; I am persuaded that the black blood continues to
be pushed on for some time by the aorta, and that its influx into
the organs is the occasion of their death; that the organs die in
fact, not because they do not receive blood, but because they do
not receive red blood; in a word, that they are penetrated by the
material cause of their death; so much so, that we may asphyxiate
any isolated part at will, by injecting it with venous blood while
all the others shall continue to receive the red blood of the
heart. At present I shall inquire into the phenomena of the contact
of the black blood with the parietes of the ventricle, and refer
the reader to the following chapters, for its effects upon the
other parts.
The movements of the heart may be stopped and made to cease
altogether from the influence of the venous blood in two
ways.--1st. As Goodwyn has said, because the left ventricle is
not excited by it upon its internal surface.--2dly. Because such
fluid, when carried into the substance of the heart by the coronary
vessels, must act upon the muscular fibre of the heart in the
same way as it does upon the other muscles. Now, for my part, I
am assured that the black as well as the red blood, will excite
into contraction the internal surface of the aortic ventricle. The
following observations and experiments will confirm my assertion.
1st. If asphyxia were to be followed by the consequences which
Goodwyn has supposed, it should influence the heart in the first
place; the annihilation of the functions of the brain, as in
syncope, should be only secondary; nevertheless, asphyxiate an
animal, by stopping up the trachea, by placing him in a vacuum, by
opening the chest, or plunging him into carbonic acid gas, and it
will in every instance be observed, that his animal life is the
first to be interrupted, and that the creature externally is dead;
but that within the heart continues for some time afterwards to
act, and the pulse to be felt.
In this way the symptoms of asphyxia are not the symptoms of
syncope. In the latter the cardiac and cerebral actions are
suspended at the same instant, in the former the heart survives,
as in cases of strong concussion of the brain for many seconds. It
follows, that in asphyxia, the different organs do not cease to
act, because the heart has ceased to supply them with blood, but
because it no longer supplies them with that sort of blood by which
they can be stimulated.
2dly. If the trachea of an animal be stopped, and an artery
opened, the colour of the blood which it emits, will gradually be
changed, and at last become as black as that of venous blood. Now,
notwithstanding this phenomenon, which is as apparent as it can be,
the fluid for some time afterwards is thrown out full as strongly
as it would be, were it red. I have seen a quantity of black blood
discharged in this way, more than sufficient to kill the creature
from hæmorrhage; were it not already dead, in consequence of its
asphyxiated state.
3dly. In the last-mentioned experiment, it may, indeed, be alleged,
that some remains of air in the air cells, might, as long as the
black blood continued to flow, have communicated to it a principle
of excitement; but to put it out of all doubt, that the venous
blood does really pass into the aortic ventricle, unaltered in its
passage from the corresponding cavity, the air may be entirely
pumped out of the lungs with a syringe, by exposing the trachea, in
the first place, and then adapting the instrument to the transverse
section of the tube; after this, let the carotid be opened; now
as soon as the red blood contained in this artery is exhausted,
the black blood will succeed to it, and that, without undergoing a
variety of gradations in colour; in this case also for a time, the
jet will be very powerful, and only be gradually weakened; but if
the black blood were not an excitant to the heart, its interruption
should be immediate.
4thly. The following is another proof of the same nature. Expose
the breast on one side by sawing exactly through the ribs before
and behind: when this is done, the lungs on that side will
collapse. Proceed to open one of the pulmonary veins; fill a
syringe warmed to the temperature of the human body with venous
blood, then push it into the red-blooded ventricle. Now, according
to the common opinion upon the subject of asphyxia, such fluid
should at least diminish in a sensible way, the movement of that
cavity, notwithstanding which, in four successive experiments, I
could not observe any such diminution. On the contrary, in one
of them, on pushing the piston, the strokes of the heart were
augmented in number.
5thly. If the black blood be not an excitant to the heart, it can
only want such power, because it contains more carbon and hydrogen,
than the red blood;[83] but if the heart of an animal, which has
been killed expressly for the experiment, by lesion of the brain or
of the lungs, has ceased to beat, it may, notwithstanding, be made
to contract as long as it preserves its irritability, by throwing
into the aortic ventricle either hydrogen gas, or carbonic acid
gas. It follows, that neither hydrogen gas nor carbon can act as
sedatives to the heart.
The experiments which I made and published last year, on the
emphysemata, produced in different animals with these gases, have
established the same truth with respect to the muscles, since they
do not cease to move in consequence of such experiments, and after
death, preserve their irritability as they usually do.
Lastly. I have often succeeded in re-establishing the contractions
of the heart, which have been annihilated in different sorts of
violent death, by the injection of black blood into the red-blooded
cavities, with a syringe adapted to one of the pulmonary veins.
Thus it is proved, that the red-blooded heart does actually push
the black blood into all parts of the body; and in this way is the
colour given to the different surfaces, of which, in one of the
following chapters, I shall offer a sketch.
Neither does the simple presence of the black blood act in a more
sedative way upon the internal surfaces of the arteries.[84] If,
in fact, while the tube adapted to the trachea is shut, the blood
be made to flow from an artery of the foot, it will be thrown out
for some time, with the same force which it would have been, were
the pipe to be open. The action, then, which it exercises in its
passage from the heart, upon the parietes of the arteries, does not
diminish the energy of these parietes. When this energy decreases,
it is at least in part from a different cause.
From the above experiments we may conclude, that the black blood
arriving in mass at the red-blooded ventricle, and correspondent
arterial system is able, from its sole contact with them, to
occasion the action of these cavities; we may be equally certain,
that were not the functions of these parts suppressed from other
causes, the circulation would continue to be made in a very
sensible manner, at least, if not with force.
Of what nature, then, are the causes which interrupt the
circulation in the heart and arteries when they are supplied with
venous blood? for when this has been flowing for some time, the jet
of it is gradually weakened, and ceases at last entirely; yet if
the cock of the pipe be opened, it will be restored with vigour.
I am persuaded that the black blood acts upon the heart as it
does on all the other parts, as we shall see that it affects the
brain--that it affects the voluntary muscles, the membranes, and
the system in general; the tissue of which it penetrates and
operates within it as a debilitant upon each individual fibre. I am
fully of opinion, that the circulation would be almost as quickly
interrupted as in the preceding cases, were it even possible to
supply the coronary arteries of the heart with red blood, while the
black blood is transmitted to the various parts of the body by the
aortic auricle and ventricle.
The black blood operates by its contact with the fleshy fibres, at
the extremity of the arterial system and not by its contact with
the internal surface of the heart. Thus it is only by little and
little, and when each fibre has been as it were injected, that
the powers of such fibres diminish and cease. On the contrary
supposition, their cessation and diminution should be almost sudden.
It may be demanded in what manner the black blood acts at the
extremities of the arteries, upon the fibres of the different
organs. Is it upon the fibres themselves, or upon the nerves
which are distributed to them? I am rather inclined to suppose
the latter to be the fact, and to consider asphyxia as an effect
produced in general by the black blood upon the nerves, which
every where accompany the arteries of a certain diameter: for as
we shall presently see, the debility which in such case the heart
experiences, is only a particular symptom of a disease in which the
organs in general are the seat of a like debility.
It might be demanded also in what way, that is to say, by what
manner of influence, the black blood acts upon the nerves or
fibres. Is it from the principles which it actually contains, or
from the absence of those which are proper to the red blood? Is
oxygen the principle of irritability--are hydrogen and carbon the
reverse?
These questions have been sufficiently disputed.--Let us stop when
we arrive at the limits of rigorous observation. Now, I think, that
we shall establish an assertion the most strictly conformable with
such principle, in saying generally and without determining the
manner, that the heart ceases to act, when the chemical functions
of the lungs are interrupted, because the black blood with which
its fleshy fibres are penetrated, is not of a nature to keep up
their action.
From this manner of regarding the phenomena of asphyxia with
relation to the heart, it is evident that both the ventricles
should be equally affected by it, because their parietes must be
equally injected with venous blood. Nevertheless, it is constantly
observable, that the movement of the red-blooded heart is the
first to stop; that the black-blooded heart in every case the
ultimum moriens; but this phenomenon does not suppose a more
real, a more decided debility in the one, than in the other
heart; for as Haller observes, the fact is common to every kind
of death in the red-blooded animal, and not the case particularly
in asphyxia.--Besides, were the red-blooded heart the first to
be absolutely affected, as the theory of Goodwyn supposes, the
following would be the appearances on opening the asphyxiated
subject.--1st. A distension of the corresponding auricle and
ventricle, by the black blood which they would not be able to expel
into the aorta.--2dly. An equal fulness of the pulmonary veins and
lungs.--3dly. A consequent fulness and swelling of the pulmonary
artery and the black-blooded cavities. In a word, the congestion of
the blood should be the greatest in that of its reservoirs, whose
action is the first to cease.
But this is contrary to observation--for 1st. In the asphyxiated
subject, the red-blooded cavities and pulmonary veins, contain but
a very small quantity of blood in proportion to that which distends
the opposite heart. 2dly. The place where the blood has stopped,
is found to be principally in the lungs, in the lungs must we
begin to follow its accumulation into the venous system. 3dly. The
arteries are as full of blood as their correspondent ventricles,
and consequently it cannot be in the ventricle more than elsewhere,
that death has been begun.
But what is the reason why the black-blooded heart is the last to
beat? because, says Haller, it is the longest excited; because it
contains a greater quantity of blood; because the blood is sent
into it from the largest veins of the system, and regurgitates from
the lungs. The famous experiment is well known by which in emptying
the black-blooded cavities, and tying the aorta so as to retain
the blood within the red-blooded cavities, the contractions of the
latter are prolonged so much beyond the contractions of the former.
But in this experiment it is manifestly the black blood which
accumulates in the aortic auricle and ventricle, because the breast
must be preliminarily opened, and therefore the lungs collapse.
Should a more direct proof be required, immediately before the
experiment, let the trachea be closed with a syringe, and the air
of the lungs be voided; the experiment will just as well succeed;
besides, the operator to be sure of the colour of the blood in the
aortic cavities, has nothing more to do than to open them, as soon
as he has finished his experiment.
We shall conclude that the black blood is almost as powerful a
stimulus as the red blood to the inner surface of those cavities,
which usually contain the latter only: the reason why they are
the first to be arrested in their action, is, because they do not
receive so large a quantity of blood as the others.
Notwithstanding what I have said, I do not entirely reject the
idea of the red-blooded ventricle being not excitable by the black
blood. It may indeed be less excitable by this sort of blood, than
by the other; but I believe that the preceding considerations will
reduce this difference of excitement to a mere trifle.
The following, however, is an experiment where such difference
would appear to be very manifest. If a stop cock be adapted to the
trachea, and an artery opened, the blood will blacken, and continue
for some time to be thrown out with its ordinary force, but at
last the jet will gradually grow weaker. If, after this, the air
be admitted, the blood will almost immediately become red and its
jet be visibly augmented. In this case the sudden augmentation
appears at first to depend upon the simple contact of the red fluid
with the sides of the aortic ventricle, since it has not had the
time to penetrate the tissue of the heart; but let things be a
little attentively examined, and it will soon be seen that this
impetuosity of impulse, depends on the movements of inspiration and
expiration, to which the animal is obliged, on the admission of
air into the lungs. The heart excited at its exterior, and perhaps
a little compressed by these movements, is the occasion of such
phenomenon, and expels the blood with a force which is far beyond
that which results from its habitual contractions.
What I have here advanced is proved, by the manifest diminution of
the jet, as soon as once the lungs have taken on their accustomed
degree of action. Besides, the influence of a series of full
expirations may be manifested without dividing the trachea. Open
the carotid and precipitate the respiration of the animal by
tormenting it (for pain will constantly have this effect) and the
jet of blood will be visibly increased. The same augmentation may
be artificially produced, by suddenly compressing the parietes
of the thorax. These experiments succeed best on animals already
weakened by the loss of a certain quantity of blood.
In the ordinary state of health however, a series of strong
expirations will not be found to quicken the pulse. Of this I
cannot assign the reason.
From what we have now said, it follows, that the experiment, in
which, on the opening of the cock of the syringe, the blood is
thrown out with augmented force, is not so conclusive as might at
first be imagined. I confess that it embarrassed me much for many
days, I hold then my former conclusions to be good.
In the red and cold-blooded animals, the action of the lungs has
not so immediate a connexion with that of the heart, as it has in
the red and warm blooded animals.
I tied the lungs of two frogs at their basis, having previously
exposed them, by incisions made laterally into the breast, the
circulation however continued as usual for a considerable time.
After this experiment, I have seen on opening the breast, the
movements of the heart precipitated, a circumstance depending no
doubt upon its contact with the air.
I shall finish this chapter by the examination of an important
question, and inquire into the reason, why when the chemical
functions of the lungs are stopped, the pulmonary arteries, the
black-blooded cavities of the heart, and in a word all the venous
system, are found so much more full of blood, than the aortic
system. In such case the circulation appears at first to be
interrupted in the lungs, and then in the other parts, according to
their proximity to the lungs.
This phenomenon must have been observed by all who have opened the
asphyxiated subject. It has been explained by Haller and others,
from the tortuosity of the vessels; but this opinion I have
sufficiently refuted.[85]
But before I proceed to assign a more real cause, I shall observe,
that the lungs, (when the blood is first arrested, because it
finds in them the first obstacle to its progress,) are found in a
singularly various state, according to the kind of death of which
the individual has died. In sudden, in instantaneous death, neither
the lungs, nor the black-blooded heart are very much distended.
I have observed this fact, 1st. In the bodies of two persons who
had hanged themselves and were brought into my amphitheatre. 2dly.
On two subjects who had fallen into the fire, and were instantly
suffocated. 3dly. On dogs which I have suddenly drowned. 4thly.
Upon guinea-pigs, which I have killed in a vacuum, or in different
gases, or otherwise.
On the contrary, arrest the phenomena of respiration in a gradual
manner; drown the animal by plunging him in water, and taking him
out alternately, asphyxiate him by placing him in a vessel of gas
imperfectly closed, continue as long as possible such state of pain
and anguish, and the lungs will be found extremely full of blood.
Between the extreme fulness, and the almost complete emptiness of
the pulmonary vessels, there is a variety of degrees; now by the
manner in which we kill the animal, we can determine any one of
these degrees at will: It is in this way that we must explain that
state of fulness in the lungs of such subjects, as are usually
brought into our amphitheatres: in the greater number of cases, the
attacks of death are slow and gradual.
But whatever be the state of the lungs in the asphyxiated subject,
the venous system is full of black blood, especially about the
heart. In this respect, there is always a very wide difference
between the veins and the arteries, and accordingly the blood must
find in the lungs the principal obstacle to its circulation: such
obstacle, as we have said, does not proceed from the tortuosity,
and state of collapse in the pulmonary vessels; its causes are
relative, first to the blood, secondly, to the lungs, thirdly to
the heart.
The principal cause depending on the blood, consists in the great
quantity of this fluid, which passes from the arteries into the
veins. In fact we shall soon see, that the black blood when it
circulates in the arteries, is not capable of furnishing the
materials of secretion, exhalation, or nutrition, or if it be so,
that it is not a stimulus to the organs which are the agents of
these functions.[86]
It follows as a necessary consequence, that the portion of fluid
which is usually taken up from the arterial system by these
different functions, flows on into the venous system, together
with the portion which should naturally pass thither; hence
there must be contained a greater quantity than usual in the
veins; and therefore a greater difficulty be experienced in its
passage through the lungs. Practitioners in opening the bodies of
asphyxiated persons, have always remarked the abundance of blood
which is met with there. The fact has been particularly remarked by
Portal, and I have always found it in my experiments.
The causes of obstacle to the passage of the blood proceeding from
the lungs, are first the non-excitement of this organ by arterial
blood. In asphyxia, the bronchial arteries are penetrated by the
black blood as well as the rest. Hence its obscure and dusky colour
in this case. This colour and its successive shades, may be easily
remarked in the collapsed lung, when the chest is opened; but in
asphyxia, such blackness is principally owing to the colour of the
blood, contained in the pulmonary veins.
The black blood when circulating in the bronchial vessels, produces
upon the lungs the same effect which it does in the heart, by
penetrating the coronary arteries; it weakens the different
parts--impedes their action, and the capillary secretions which
should be made there, from the tonic powers of the organ.
The second cause of obstacle to the circulation, when the chemical
functions of the lungs are interrupted, is the non-excitement of
the organ by vital air. The first effect of such air upon the
mucous surfaces of the air-cells, is to stimulate them, and so to
keep them up in a sort of perpetual erethism.[87] In the same way
are the powers of the stomach brought into action by the presence
of aliment there, and those of every reservoir of the body, by the
influx of their accustomed fluids. Again, such excitement of the
mucous surfaces by foreign substances keeps up their tone. The
privation of such excitement, therefore, must put a stop to their
capillary secretions, which depend upon their tonic powers.
The different aeriform fluids which take the place of the
atmospheric air in the different sorts of asphyxia, appear to act
very differently upon the tonic powers, or the insensible organic
contractility of the lungs. Some of these put a sudden stop to the
circulation, others not. Compare the asphyxiæ produced by nitrous
or sulphurated hydrogen gas, with those which may be occasioned
by pure hydrogen, or carbonic acid gas, and the difference will
instantly be seen. This difference indeed, as well as the various
other phenomena observable in the various asphyxiæ, depends on
causes which we have not mentioned, but the affection of the
air-cells, is evidently one of them.
Lastly, the third cause of stagnation of the blood in the
venous vascular system, is that debility, which takes place in
the ventricle and auricle of this system, when penetrated with
venous blood: on the influx of the blood from the cava, they
are consequently distended, and this is the case also with the
cava itself, for the very same reason. The causes which are now
assigned, are sufficient to shew why the black-blooded system, is
gorged with fluids in asphyxiæ.[88] The following considerations
will shew why the red-blooded system contains a lesser quantity of
fluid.
1st.--The obstacle commences in the lungs; therefore the aortic
heart must receive a less quantity than usual: hence, as we have
seen, proceeds the quicker cessation of the contractions of this
ventricle.
2dly.--The natural strength of the arteries, though enfeebled
by the influx of blood into their parietes, is much superior to
that of the veins, which besides are subject to the same cause of
debility.[89] Accordingly these vessels and the aortic ventricle,
are capable of surmounting the resistance of the capillary vessels
of the body in general, much more easily than the veins and the
venous ventricle, are of vanquishing the capillaries of the lungs.
3dly.--In the general capillary system, there is only one cause of
want of action, viz. the presence of black blood in it; to this in
the lungs there is added another cause, the want of that habitual
excitement which this organ receives on the part of the atmospheric
air: accordingly in the lungs, there is a greater resistance
offered to the influx of the blood, and with respect to the heart,
a less capability of surmounting such resistance. In the other
parts, the contrary of all this is observed, a less resistance to
the influx of the blood from the arteries into the veins on the
one hand, and on the other a greater capability of overcoming such
resistance.
4thly.--In the general capillary system, which is continued on from
that of the arteries, if the circulation be embarrassed at first,
in any organ in particular, it may still continue to go on in the
other organs, more or less, in which case the blood regurgitates by
these others into the veins. On the contrary, as all the capillary
system, which is the continuation of the general venous system,
is concentrated in the lungs, the venous circulation must be
suppressed, whenever this organ loses its powers.
The preceding considerations, if I am not mistaken, explain why
the vascular systems are so unequally full of blood after death, a
circumstance, which is common to almost every disease, as well as
the asphyxiæ.
In the latter sort of death however, although the general capillary
system presents a less degree of resistance than is made by the
capillary system of the lungs, nevertheless such resistance arising
from the influx of the black blood into the organs in general is
very manifest, and produces two remarkable phenomena.
The first is a greater quantity than usual of black blood in the
arteries, and therefore a greater difficulty of injecting these
vessels. Such blood is seldom coagulated. Indeed in all cases the
venous blood is much less coagulable than arterial blood. This fact
is proved, 1st, By the experiments of modern Chemists. 2dly, By the
comparison of the blood of varices with that of aneurisms. 3dly, By
the inspection of that which usually stagnates after death in the
veins of the neighbourhood of the heart.
The second circumstance, to which I have referred, is the general
livid colour of the greater number of the surfaces, with the
fulness of divers parts, such as the face, the tongue and lips.
These two phenomena indicate a stagnation of the blood at the
extremities of the arteries, in the same way as they denote the
same effect in the pulmonary vessels; here there is a much more
evident repletion, because as I have said, the capillary system is
there concentrated within narrow limits.
The reflux of the blood of the veins towards the extremities is the
reason assigned by authors for the livid appearance of asphyxiated
persons. There is little reality in this cause: in fact, this
reflux, which is very sensible in the trunks of the veins,
diminishes continually towards their ramifications, where it is
impeded and rendered impossible by the valves, besides which, the
following experiment is an evident proof, that we must attribute
the lividity in question, to the impulse of the black blood from
the aortic ventricle.
1st.--Adapt a syringe with its stop-cock to the divided trachea.
2dly, Open the abdomen so as to distinguish the intestines and
epiploon. 3dly, Shut the cock. At the end of two or three minutes,
the red tint which animates the peritoneum, and which is borrowed
by this membrane from the vessels, which creep underneath it,
will be changed into a dull brown colour. This colour may be made
to disappear and re-appear at will, by opening or shutting the
syringe.
Here we cannot, as if the experiment were made upon other parts,
suspect that a reflux is propagated from the right ventricle
towards the venous extremities, since the mesenteric veins,
together with the other branches of the vena portæ, form a system
apart, independent of the great black-blooded system, and having no
communication with the cavities of the heart which correspond with
this system.
But I shall touch again upon this subject. The above experiment is
amply sufficient to prove, that the lividity of the surfaces of the
body is owing to arterial impulse.
At present we are in a condition to explain how the lungs are more
or less gorged with blood, more or less livid, and how the livid
spots upon the different parts of the body are more or less marked
accordingly as the asphyxia has been more or less prolonged: for it
is evident, that if before death, the black blood have gone round
the two systems ten or twelve times, it will inject the extremities
much more than if it had made such circulation only two or three
times; at each revolution, a greater or less quantity will be left
in the extremities, for want of action in the capillary vessels.
In finishing this chapter I shall take occasion to observe, that
the spleen is the only organ of the economy susceptible like the
lungs of assuming a very great variety of volume. Scarcely is
it ever found in the same state. It has been falsely supposed
that there is a relation between the plenitude or vacuity of the
stomach, and the inequalities of the spleen; but this is not the
case, as I have said elsewhere. Such inequalities during the life
of the body do not exist, and supervene only at the instant of
death.
It appears to me, that they depend especially upon the state of
the liver, the capillary vessels of which, are the continuations
of all the branches of the vena portæ as the capillaries of the
lungs are those of the great venous system. Thus, when the hepatic
capillaries from any cause whatever are enfeebled, the spleen
must swell and be filled with the blood, which cannot traverse
the liver.[90] In such case, if I may so express myself, there
is an isolated asphyxia of the abdominal vascular apparatus. The
liver being to the spleen, what the lungs are to the black-blooded
cavities in common asphyxia. The resistance is in the former, the
stagnation in the latter. But this matter may be better understood
hereafter. Experiments upon animals killed in different ways, would
throw much light upon it, and these I purpose undertaking. By these
means we may rigorously establish the analogy existing between
the stagnation of the blood in the different branches of the vena
portæ, and that which is observed in the general venous system,
in consequence of various kinds of death. With respect to the
spleen and its system of veins, in ordinary asphyxia, I have never
remarked in it any peculiarity.
FOOTNOTES:
[79] It is not because the vessels of the lungs have become
tortuous that the blood flows through them with difficulty, but
because they are compressed. It was needless for Goodwyn to seek
for reasons to prove, that the flattening of the lungs does not
offer a mechanical obstacle to the course of the blood. If he had
observed with attention the phenomena of respiration, he would have
seen that this contraction, if it does not completely interrupt
the circulation of the blood in the lungs, at least modifies it
in a very remarkable manner. When the lungs contract, not only
the bronchial cells are flattened, but the pulmonary vessels are
compressed, and tend to expel the blood contained in their cavity.
This fluid flows back then on one part towards the right ventricle
by the pulmonary artery, and on the other it accumulates in the
pulmonary veins before entering the left auricle. Hence we see that
the jet by the carotid artery must increase rather than lessen in
the last moments. But if the compression continues, as the capacity
of the ramifications of the pulmonary artery is diminished as
well as that of the veins of the same name, the quantity of blood
which passes through the lungs is less, and the jet by the carotid
necessarily decreases. The experiment related by Bichat is then
entirely opposed to the opinion which he advances.
It is not only by influencing the course of the blood in the system
of pulmonary vessels that the alternate motion of the thorax
modifies the circulation. If we lay bare the jugular vein of a dog,
we perceive that the blood does not move in its cavity from the
sole influence of the right auricle, but in an evident manner from
the influence of the motions of respiration also.
At each time that the thorax is dilated in inspiration, the vein
is quickly emptied, flattened and its parietes are sometimes
brought exactly against each other; it swells on the contrary and
fills with blood when the thorax contracts. A similar phenomenon
takes place in the venæ cavæ. In order to render it evident it is
sufficient to introduce by the jugular vein into the venæ cavæ a
sound of gum elastic; we then see that the blood flows through
the extremity of the sound only during the time of expiration. A
similar effect is observed if we introduce a sound into the crural
vein and direct it towards the abdomen.
Haller and Lorry have paid much attention to this phenomenon, and
have proposed an explanation of it which seems very satisfactory
at first view, though it is really imperfect. When the thorax is
dilated, say they, it draws the blood from the venæ cavæ, and, by
degrees, that of the veins which are near it. The mechanism of
this inspiration is very similar to that by which the air is drawn
into the trachea. When the thorax contracts, on the contrary,
the blood is crowded back in the venæ cavæ by the pressure which
is made on all the pectoral organs, vessels, heart and lungs, by
the expiratory powers, and by degrees arrives at the veins which
terminate in them. Hence the alternation of vacuity and fulness
which the jugular veins exhibit.
If we open an artery, and examine with attention the jet of blood,
we see that it increases in expiration, and this is especially
evident when the animal expires strongly or makes an effort; but
as we cannot always produce these efforts at will, or a great
inspiration, we can in some measure imitate the phenomenon and
produce the contraction of the lungs by compressing with the hands
the sides of the thorax; we see then the jet of arterial blood
increase or diminish, in proportion to the pressure that is made.
If respiration produces this effect on the course of the blood in
the arteries, it is natural to think that it can influence the
course of the venous blood, not only by means of the veins, as
Haller and Lorry thought, but also by means of the arteries. For
the purpose of satisfying myself, I made the following experiment,
I tied the jugular vein of a dog; the vessel became empty below the
ligature, and swelled much above, as uniformly happens. I punctured
slightly with a lancet the distended portion, so as to make a very
small opening. I obtained in this way a jet of blood, which the
ordinary motions of respiration did not modify evidently, but which
trebled or quadrupled in size if the animal made any considerable
effort.
It might be objected, that the effect of respiration was not
transmitted by the arteries to the open vein, but by the veins
which were free, and which would have transmitted the blood of the
venæ cavæ, towards the tied vein, by means of anastomoses. It is
easy to remove this difficulty; in fact, in the dog the internal
jugular vein is, as it were, but the appearance of a vein, and
the circulation of the head and neck is performed almost entirely
by the external jugular veins, which are very large. By tying
at the same time these two veins I was sure of preventing, in a
very great measure, the reflux which has just been spoken of;
but so far from the double ligature diminishing the phenomenon
before stated, the jet becomes on the contrary more strictly in
relation with the motions of respiration, for it was evidently
modified, even by common respiration; which, as we have seen, does
not happen in the case of a single ligature. In order to render
the thing more evident, I tried it on the crural vein; this vein
and all its branches being furnished with valves, which oppose
a reflux, if this phenomenon of the increase of the jet appears
during expiration, we might be sure that the impulse came from the
arteries. This is what I have observed in fact in many experiments.
The crural vein being tied and punctured below the ligature, the
jet which is formed increases evidently in powerful expirations, in
the efforts and the mechanical compressions of the parietes of the
thorax with the hands.
We see by this and the preceding experiments, that we cannot adopt
without modification the expression of Haller and Lorry relative to
the swelling of the veins. This swelling takes place, not only, as
they say, by the flowing back of the blood of the venæ cavæ into
the branches which open into them mediately or immediately, but
also by the entrance into the vein of a greater quantity of blood
coming from the arteries.
[80] As in dead bodies the air within and the air without are of
the same temperature, the lungs, when they are full of it, do not
flatten when the thoracic cavity is opened. There is usually then
a space between the parietes and the contained organs; this is not
because we die in expiration; for as the lungs empty themselves,
the ribs and intercostal muscles rest upon them; it is because
the pulmonary air, in cooling occupies less space, and the cells
contracting gradually as the cooling takes place, diminish the
whole size of the organ. A vacuum is then made between the pectoral
and pulmonary portions of the pleura.
It is thus that, under some circumstances, the brain flattening and
lessening after death, whilst the cavity of the cranium remains
the same, a vacuum is formed between these two parts, which then
exhibit an arrangement different from that of the living organs. If
the sacs without an opening, as the peritoneum, tunica vaginalis,
&c. never resemble, in this respect, the pleura and arachnoides; if
their different surfaces are always contiguous after death, it is
because the abdominal parietes or the skin of the scrotum, unable
to resist the external air, flatten by pressure, and are brought
against the internal organs, as the diminution of these tends to
form a vacuum.
It is to this vacuum existing in the pleura of dead bodies, that
must be referred the following phenomenon, which is always observed
when the abdomen is opened and the diaphragm dissected. In fact, as
long as no opening is made in this muscle, it remains distended and
concave, notwithstanding the weight of pectoral viscera which rest
upon it in a perpendicular situation, because the external air,
which presses the concavity of it, forces it then into the vacuum
in the thorax, which never exists during life. But the instant the
air is admitted by a cut of the scalpel, this muscular partition
flattens, because the equilibrium is established. If all the air is
drawn from the lungs by a syringe, the diaphragmatic arch is still
more evident.
There is then this difference between the opening of a dead body
and that of a living one, that in the first the lungs are already
flattened, and in the second they flatten at the instant of
opening. The contraction of the cells, from the condensation of
the air by cooling, is an effect of the contractility of texture
or from want of extension, which as we have said, continues in a
degree with the organs after death.
Besides, if the lungs flattened in the dead body the instant
the thorax was opened, it would be owing to the pressure of the
external air, a pressure which would expel through the trachea what
was contained in these organs. Now if, to prevent the escape of
air, you close hermetically the canal by fixing a tube to it the
stopper of which is tight, and the thorax is afterwards opened, the
lungs still flatten; the air had already gone out of them. Make,
on the contrary, the same experiment on a living animal, you will
always prevent the flattening of these organs, by preventing the
expulsion of the air.
In this point of view Goodwyn has gone on a wrong principle in
measuring in a dead body, the quantity of air remaining in the
lungs after each expiration. Besides, if you open bodies ever
so little, you will hardly find two in which there is the same
arrangement in the lungs. The infinitely various manner in which
life terminates, by accumulating more or less blood in these
organs, by retaining more or less air in them, &c. gives them so
variable a size, that no general data can be established respecting
them. On the other hand, can we hope to be more successful on the
living body? No; for who does not know that digestion, exercise,
rest, the passions, tranquillity of mind, sleep, watchfulness,
temperament, sex, &c. make an infinite variety in the forces of the
lungs, the rapidity with which the blood circulates through them,
and the quantity of air that penetrates them? All the calculations
on the quantity of this fluid which enters or goes out according to
the inspiration or the expiration, appear to me to be physiological
errours, inasmuch as they assimilate the nature of vital forces
with that of physical forces. They are as useless to science as
those which had formerly for their object the muscular force, the
velocity of the blood, &c. Besides, observe if their authors agree
better among themselves then they used to do on this much agitated
point.
[81] It is inconceivable how Bichat could think of confirming his
opinion by the example of hydrothorax. Who does not know that when
an effusion takes place in the cavity of one of the pleuras, that
that portion of the lungs only which is above the level of the
water serves the purposes of respiration; that when the effusion
has arrived to the summit of the cavity, the lungs of that side,
which can no longer dilate, are of no use in respiration; and
those of the other, being compelled alone to make the necessary
modifications in the blood, must be traversed by the greatest part
of this fluid? It is known, finally, that in this case the patient
cannot lie down an instant on the sound side, because this position
prevents the dilatation of the lungs of that side which alone
serve for respiration, and the danger of suffocation is therefore
imminent.
[82] The observation of Bichat is very just; and I have myself
often observed in cases of apoplexy, that the motions of the heart
continue many hours after the arteries contain only black blood.
[83] At the period Bichat wrote, it was impossible to know whether
the arterial or venous blood contained most hydrogen and carbon.
At the present day even, when the means of analysis are much more
perfect and animal chemistry farther advanced, we are hardly better
informed.
[84] It seems that when Bichat wrote this work, he had not fixed
in his own mind what part the arteries take in the circulation;
at least, in this paragraph, he seems to give them a contractile
power, which, in his other works, he accords only, to their
ultimate ramifications.
[85] It is certain, whatever Bichat may say concerning it, that
numerous angles in the course of a blood-vessel, by increasing
the friction, must retard the course of the fluid which runs
through its cavity. We may in fact believe that it is one of the
causes, which, in the flattening of the lungs, embarrass the
circulation; this cause exerts its action principally upon the last
ramifications of the pulmonary artery which, by their interlacing,
form the bronchial cells; another more powerful cause, which acts
equally on the divisions of the vein and the artery is, as we have
said, the pressure made on the lungs by the flattening of the
thorax, and the elevation of the diaphragm.
[86] See the article on the influence of the lungs on all the
parts. I am compelled here to deduce consequences from principles
which I shall prove hereafter; such is in fact the connexion of
questions which have the circulation for their object, that the
solution of one draws as a necessary consequence that of all the
others. It is a circle in which it is always necessary to suppose
something, leaving it to be proved afterwards.
[87] I cannot see what can have induced Bichat to admit this
erethism of the lungs, the use of which cannot be imagined. It
is quite enough to suppose in the organs the existence of those
concealed properties, when there is need of them to explain their
functions.
[88] As the blood flows in the veins in a continuous motion, the
distension of these vessels does not take place in the direct
motion of the blood, but in its retrograde motion. Every time the
right auricle contracts, a portion of blood, instead of passing
into the ventricle of the same side, is forced back into the
superior and inferior venæ cavæ, and into the principal venous
trunks which open into them. By this reflux of the blood, these
veins are dilated, and have a pulsation which is easily seen in the
jugular in very thin people. This pulsation has received the name
of the _venous pulse_. When it is very evident, it may indicate an
obstacle to the passage of the blood from the auricle to the right
ventricle.
Another reflux of the blood in the veins corresponds with the
moment of expiration, and is perceptible even longer. We shall soon
have to speak of it, in speaking of the _movements_ of the brain.
[89] _The natural force of the arteries_ is not dependent on life,
and consequently cannot be enfeebled by the entrance of black
blood. This force is nothing but elasticity, which indeed ceases to
be in action as soon as death takes place, but which does not cease
to exist till the texture itself is destroyed and disorganized. As
this property is very conspicuous in the arteries, it is sufficient
to drive the blood from their cavity at the instant of death,
whilst it is too feeble in the veins to expel this fluid entirely.
Thus it is, that we find blood in the veins only, after death.
[90] The state of the spleen in the dead body may become in some
measure an index of the state of the circulation during the last
moments of life. The swelling of it shows almost always the
embarrassment of the circulation; and not only in an insulated
system, such as that of the vena portæ, as Bichat considers it, but
in the whole pulmonary system.
When any cause impedes the circulation in the capillaries of the
lungs, it necessarily produces a stagnation of the blood in the
divisions of the pulmonary artery, and by degrees the disturbance
is felt even in the two venæ cavæ, but especially in the inferior
in which the blood rises against its gravity. The blood accumulates
in the principal branches; the veins of the liver and kidneys swell
more or less; as to these organs themselves, the firmness of their
texture hardly allows them to be distended, so they do not increase
sensibly in size, or if this increase takes place, it is slow.
It is not the same with the spleen; the looseness of its texture
will admit a great quantity of liquid, and its size can thus be
doubled or trebled in a very short time. It becomes then a kind
of reservoir, in which is accumulated the blood which cannot pass
through the lungs.
It may be objected to what we have just said, that oftentimes in
phthisis the greatest portion of the lungs has become incapable of
allowing the blood to pass, and that yet after death, the spleen
is found in a natural state. But it should be recollected, that
phthisical patients have, during the latter part of their lives,
but very little blood, so that each portion sent by the right
ventricle always finds a sufficient channel for it in the lungs.