Chapter II

OF THE INFLUENCE OF THE DEATH OF THE HEART, OVER THAT OF THE BRAIN.

I shall evidently have determined what is the mode of this influence, should I be enabled to establish in what way the action of the heart is necessary to that of the brain; for in this instance the cause of death will be no other than the privation of the cause of life. Now the heart can only act upon the brain in two ways; by the nerves, or the vessels which serve as their connecting medium. In fact these two organs have no other means of communication.

It is evident that the nerves cannot be the agents of such actions; it is the province of the brain to act by means of the nerves. The different parts of the body never influence the brain by such means, excepting in the sympathies. If a bundle of nerves belonging to the voluntary muscles be tied, the muscles indeed will cease to act, but nothing will be changed in the cerebral mass.[56]

I have ascertained by many experiments that the phenomena of galvanism, which are propagated so energetically from the brain towards the organs, which descend, if I may so express myself, along the nerve, will hardly ascend in a contrary direction. Apply the apparatus to a nerve of the loins and the muscles of the upper limbs, and when the communication is made, there will be scarcely any contraction; but on the establishment of a communication between the same nerve and the lower limbs, a violent convulsive motion will instantly be occasioned. I have even observed, on placing two metallic plates, the one under the lumbar nerves, and the other under the upper limbs, that the communication of the two plates by means of a third metal, will cause a contraction of the lower limbs, while the upper limbs remain inactive, or move but feeble.[57]

These experiments are particularly applicable to the relation of the heart with the brain; for not only is it true that the section, ligature or compression of the cardiac nerves are of little effect with regard to the functions of the latter, but it is true also, as we shall presently see, that they do not directly modify the movements of the former. We may conclude that the vessels are the exclusive agents of the influence of the heart upon the brain.

The vessels, as every one knows, are of two sorts--venous or arterial--they carry black or red blood, the latter answer to the left side, the former to the right side of the heart. Now their functions being very different, the action of one of the portions of this organ on the brain, can never be the same as that of the other portion. We shall inquire in what way they both of them act upon it.

In naming these two portions, I shall not make use of the expressions of right and left to distinguish them, but of those of the red-blooded and the black-blooded heart, for each of these portions of itself is an isolated organ, distinct from that to which it is applied, and in the adult especially so. In fact there are two hearts, the one arterial, the other venous, notwithstanding which, we can hardly employ these adjectives for the purpose of designating them, since they both alike possess their arterial and venous appendages. On the other hand, they are neither of them situated exactly to the right or to the left, are neither of them exactly forwards or backwards. Besides which these latter denominations would not apply to animals.

I. _In what way does the cessation of the functions of the red-blooded heart interrupt the functions of the brain?_

The red-blooded ventricle and auricle, exert their influence upon the brain by means of the fluid which they send thither through the carotid and vertebral arteries. This fluid may excite the cerebral organ in two ways. 1st. By the movement, with which it is directed. 2nd. By the nature of its colouring principle.

It is easy to prove that the movement of the blood is necessary to the life of the brain. Expose the brain of an animal in part, and tie the carotids. In such case the cerebral movement will be sometimes weakened, and then the animal will be stupified, at other times the vertebral arteries will exactly supply the place of the carotids, and then there will be nothing deranged in the principal functions of the brain; for there is always a relation existing between the alternate rise and fall of the cerebral mass, and the energy of life which it displays.[58]

In general, the obliteration of the carotids is never suddenly mortal. Animals will live without them, at least for a certain time. I have kept dogs in this state for several days and have afterwards made use of them for other experiments: two however died in the course of six hours, after the application of the ligatures.

After having made the above experiments which go very far to the establishment of the principle which I am labouring to prove, let a piece of the cranium be taken from another animal and tie the vertebral and carotid arteries. The movement of the brain will then be entirely interrupted and the animal immediately die.

The impulse, which proceeds then from the influx of the blood into the brain, is a condition essential to the functions of this organ, but other proofs may be adduced, for the establishment of the truth of this assertion.

1st. There are a number of compressions, which can only act by preventing the brain from being duly affected by such impulse. A collection of pus, or blood, will often put a stop to all the functions, which relate to the perception, memory, and voluntary motions of the individual. Let such compression be removed and his sensibility will immediately re-appear. In such case, it is manifest that the brain was not disorganized, but only compressed, and in a state incapable of being excited by the heart.[59]

I do not think it necessary on this subject to cite cases. All authors, who have treated of wounds of the head, are full of them. I shall content myself with remarking, that the same effect may be artificially produced in our experiments upon animals, and that accordingly as the brain is compressed or free, the creature will be insensible, or the contrary. According to the degree of the compression, will be the degree of the stupor.

2dly. There are reptiles, in the brain of which no motion whatever is occasioned by the heart. The frog is of this species. On raising the upper portion of the cranium, and exposing the brain, there cannot be perceived the slightest motion. Now in this species, and that of the salamander, the influx of blood may be cut off from the cerebral organ without occasioning the immediate death of the animal. The voluntary muscles for instance continue to act; the eyes to exhibit a lively appearance, the tact also of the creature is manifest for some time after the heart has been taken away, or the double branch which proceeds from the single ventricle of these animals has been tied.[60] I have frequently repeated these experiments, and have constantly found the effect the same.

3rd. It is a general observation, that those animals which have a long neck, and in which the heart for that very reason is not so capable of exerting a lively influence over the brain, have a more limited intellect, and the cerebral functions less marked. On the contrary a very short neck, and the approximation of the heart to the brain very generally are found to coincide with the latter. Similar phenomena are sometimes observed in men. They who have the neck particularly long are dull, they who have it short, for the most part intelligent and lively.

From these many facts we may confidently assert, that one of the means, by which the heart maintains the brain in action, consists in the habitual movement, which it impresses on it.

But this movement is essentially different from that which in the other viscera, such as the liver, or spleen, is derived from the same cause. In these it is little manifest, in the brain it is very apparent; the reason is evident; the large arterial trunks of the brain, are situated at its base, between the brain and its bony parietes; in consequence of which, at each diastole, the vessels experience a resistance from the bone, which is communicated immediately to the cerebral mass. At such time the brain is really lifted, just in the same way as we see a tumour lifted by the arteries which creep along the bones beneath it; and instances of this are frequent. So apparent indeed is the motion of tumours when they are situated over the carotid, as it lies upon the vertebral column, or over the femoral artery, immediately after its passage under the crural arch, as often to occasion doubts with respect to their nature.

But no other organ is enclosed within a bony cavity; the motion of the arteries every where else, is lost in the surrounding cellular substance, or soft parts. Such motion, then, is unessential to the functions of the liver, the kidney, and other analogous viscera.

The integrity of the functions of the brain, is not only dependent on the mere motion, but on the sum also of the motion communicated. It is equally impaired by too much, or by too little motion. Of this assertion the following experiments are proofs.

1st. Inject water by the carotid of a dog; the presence of this fluid in the brain is not pernicious, and the animal will live very well, when the injection has been skilfully made. But if it be pushed with violence, the cerebral action will immediately be troubled, and often cannot be restored.[61] In every experiment, there will be found to exist a relation between the force of the impulse and the state of the brain; if the pressure be but a little augmented, its effects will be instantly seen in the agitation of the countenance of the creature; if relaxed, a corresponding calm will succeed; if increased to the highest pitch, it will immediately occasion death.

2dly. If the brain be exposed, and an artery afterwards opened, so as to produce a considerable hemorrhage, the motion of the brain will be diminished in proportion as the afflux of the blood to it is diminished, and finally will cease entirely. Now, according to all these various degrees of diminution, which may be observed in the movements of the brain, will be the corresponding weakness of the cerebral influence as it is discoverable in the state of the eyes, the touch, and the voluntary motion of the animal.[62]

Hence it is easy to see, why a state of prostration and languor is always the consequence of great hemorrhage--and from what has been said above we may conceive the reason, why the arterial system of the brain has been at first concentrated at its base, while the larger venous trunks are almost all of them situated on the convexity of its surface. The base of the brain is small and easily moved, the convexity large and little capable of transmitting motion, such as could be made upon it by vessels. Besides, it is at the lower part of the brain that exist its particular and essential forms. The lesions of these are mortal, and consequently their functions must be important. On the contrary, experiment and observation alike have proved, that very little derangement follows, from cutting or rending the substance of the upper part of this organ. Hence also we may see the reason, why its natural defences towards its base, are constituted in such way as to be almost impenetrable, and why at its upper surface, it is less protected. Now, where its life is indispensable, and its action absolutely necessary, it should naturally receive the first and undiminished impulse of its excitant. We may conclude, that the interruption of the action of the red-blooded heart is the occasion of interruption in the action of the brain by annihilating its movement.

But this movement is not the only means by which the influence of the heart is exerted on the brain; for if it were so, we might easily reanimate the enfeebled functions of the latter, by injecting it with water at the same time through both the carotids. If pushed with an equal force, the black blood and the red blood alike would be capable of keeping up its action; but this, as we shall presently see, is not the fact.

The heart, then, acts upon the brain by the nature of the fluid which it sends thither; but as the lungs are the focus, where the blood undergoes an alteration, we shall refer the examination of its influence upon the cephalic system, to the chapter in which we shall treat of the relation of this system, with that of the lungs.

II. _In what way does the cessation of the functions of the black-blooded heart interrupt the functions of the brain?_

It very rarely happens that general death commences by that of the venous auricle and ventricle. On the contrary, they are almost always the last in action, and when they cease to act, the brain, the lungs, and the red-blooded heart have already ceased to exhibit their respective phenomena. Nevertheless the contraction of these cavities may be annihilated, or rendered at least inefficacious with regard to the circulation, from the rupture of an aneurism or similar causes; in which case the brain becomes inactive and dies, as we have shewn it to do in the preceding section, from want of movement.

There is another kind of death of the brain depending on the interruption of the transmission of blood from the head to the heart, as when the jugulars are tied. The venous system, in consequence, is glutted and the brain compressed, from the continued afflux of the red blood into its arteries; but the phenomena of this sort of death are already sufficiently known.

In the present chapter it is my intention to examine a species of death, the principle of which by many physiologists has been placed in the heart, but which appears to me to affect the head only; I mean that death which may be occasioned by the injection of air into the veins.

It is generally known, that as soon as any quantity of this fluid is introduced into the vascular system, the movements of the heart are accelerated, that the creature is much agitated, cries with pain, is convulsed, and soon after deprived of its animal life, but lives organically for a certain time, and then invariably dies.[63] Now, what is the organ so readily affected by the contact of air? I affirm it to be the brain, and not the heart; and maintain that the circulation is annihilated, only because the cerebral actions have previously been so.

For, in the first place, in this kind of death, the heart continues to beat for some time after the cessation of the animal life, and consequently for some time after that of the action of the brain.[64]

Secondly, By injecting air into the brain through one of the carotids, I have caused the death of the creature just in the same way as when air is introduced into the veins; excepting only with a previous palpitation of the heart.[65]

Thirdly, Morgagni has cited a number of cases of sudden death, the cause of which should appear, from his remarks, to be the repletion of the blood vessels of the brain by air, which had been developed there spontaneously, and which he says, by its rarefaction, compressed the origin of the nerves. I cannot suppose that such compression can be effected by the very small quantity of air, which, when injected into the carotid, is sufficient to occasion death; accordingly, I should doubt whether this compression were real in the cases adduced, but for this, they are not the less important. Whatever be the manner in which it kills, air is fatal whenever introduced into the brain, and this is the essential point. It is with the fact that we have to do and not the manner.[66]

Fourthly, As often as an animal is killed by the insufflation of air into one of its veins, I have ascertained that the whole of the red-blooded, as well as the black-blooded heart, is full of a frothy blood, mixed with air bubbles; and that the carotids, and vessels of the head, contain a similar blood; such blood must act upon the brain, in the same manner as it does in the two sorts of apoplexy, of which we have just been making mention.

Fifthly, If air be pushed into one of the divisions of the vena portæ from the side of the liver, it oscillates in the greater trunks of that organ for a considerable length of time, and arrives but slowly at the heart.--In this instance I have observed, that the animal experiences, only after a certain interval, those affections which are sudden when the fluid is injected into the veins of the principal system.[67]

Sixthly, The rapidity with which, in certain experiments, the annihilation of the cerebral action succeeds to the insufflation of air into the veins, might almost persuade us that such phenomenon is occasioned, as it is in wounds of the heart and syncope;--but 1st. The most simple inspection is sufficient to shew us that the heart continues to act after the apparent death of the animal.--2dly. As the motions of the heart are prodigiously accelerated by the contact of the foreign fluid, they push on the frothy blood with an extreme velocity, and hence we have the reason, why the brain in such case is so rapidly affected.

Seventhly, Were the cerebral action in this sort of death interrupted for want of movement from the heart, it would happen as it does in great hemorrhages of the aorta; that is to say, without violent convulsion. But here, on the contrary, the convulsion is extremely violent, immediately after the injection, and consequently, announces the presence of an irritating substance on the brain.

We shall conclude, that in the accidental mixture of air with the blood of the venous system, it is the brain which dies the first, and that the death of the heart is the consequence of the death of the brain. I shall explain in another place, in what way this phenomenon is occasioned.

FOOTNOTES:

[56] It is not true that a ligature on a nerve produces its effects
only on the part to which this nerve is distributed; the brain is
also affected; for, without this, how can be explained the pain
that is felt, and the excitement, which is often sufficiently
powerful to produce convulsions, and sometimes even death.

[57] The facts related here by Bichat are not conformable to those,
which, the philosophers and physiologists have observed who have
been more particularly engaged with this kind of experiments.
Besides the consequences which he has drawn from them are not
accurate, and he seems to be ignorant what course the galvanic
fluid in this case takes.

[58] If there is always a relation between the vital energy of the
brain and its alternate motions, it is because there is a constant
relation between these motions and the entrance of the blood into
the organ. Thus then, instead of considering this shock as the
exciting cause of the brain is it not more natural to see in it
only an effect purely accidental of the arrival of the arterial
blood, which every thing proves to be the real excitant?

[59] As we know absolutely nothing of the manner in which the
intellectual phenomena are produced in the brain, we cannot
say whether compression prevents their development by stopping
the motions with which the brain is habitually agitated, or by
preventing the entrance of the arterial blood, or finally in some
other way that we do not suspect.

[60] The organization of these animals differs too much from that
of man to enable us to draw conclusions from one to the other,
especially in what concerns the functions of the nervous system.
There is an experiment of M. Dumeril in which a salamander lived a
long time after the amputation of the head, till the formation of a
perfect cicatrix in the neck, which intercepted the passage of air
to the lungs.

[61] Why are not the cerebral functions disturbed, when water is
pushed slowly into the carotids? because there is then mixed with
the blood of the artery too small a quantity of water at a time to
enable this fluid to have a very evident action on the brain. But
if this introduction of water into the mass of blood continues,
whatever precaution may be taken, its effects soon show themselves.
We have often, in our experiments, introduced a great quantity of
water into the veins of an animal, and though much of it passed
off by pulmonary transpiration, the arterial blood soon became
very aqueous. Now, we have always observed, that in this case,
the animals were struck with a kind of stupidity, which evidently
indicated a want of action of the brain.

[62] It is not uncommon to see patients, who retain their
intellectual faculties perfectly, when the motions of the heart
are so feeble, that they certainly cannot produce, in the mass of
brain, any sensible jar.

[63] A very considerable quantity of air can be forced into the
veins of an animal, without causing its death, provided it be not
pushed in suddenly. In all these cases, it is understood, that the
quantity that can be thus introduced is in proportion to the size
of the animal. I have before me at this moment the details of an
experiment that I made on a horse at Alfort with M. Dupui, and in
which, before the animal died, I was able, in thirty seven minutes,
to inject quickly into the veins forty syringes full of air, and
three syringes full into the carotid artery. (The capacity of the
syringe was seventeen centilitres.) The animal died three minutes
after the last injection. At the examination of the body, we found
air in the azygos vein and in the thoracic duct, which contained
much lymph, as well as the lymphatic vessels of the internal
surface of the lungs. The heart was enormously distended with air
mixed with a small quantity of blood.

[64] This is not correct, and death takes place, on the contrary,
by the cessation of the motions of the heart. The right ventricle
is filled with air; and this air, dilated by heat, so distends it,
that it can no longer contract.

[65] The disorders which are produced in this case do not at all
resemble those which follow the entrance of air into the veins.
If we push towards the brain, by the carotid artery, a small
quantity of air, we see almost immediately signs of a strong
cerebral congestion, spasmodic stiffness of the muscles, loss of
sensibility, and of the action of the senses, and all the phenomena
of a real apoplexy. Respiration and the circulation go on some time
without any apparent alteration, but finally these two functions
become embarrassed and the animal sinks. Every thing leads to the
belief, that the alteration in the circulation of the brain depends
here on the presence of rarefied air in the ultimate arterial
ramifications.

When apoplexy is thus produced by the injection of air, if it
be still forced into the artery, it breaks open violently a
passage for itself, it tears the small vessels, and spreads in
the parenchyma of the brain, which it makes emphysematous and
crepitating under the finger. There finally returns a portion of
it by the veins, which goes to the right cavities of the heart and
which contributes to arrest the circulation.

[66] In the two examinations related by Morgagni, it appears that
after a sudden death, there was found in the vessels of the brain
an aeriform fluid, to the presence of which, for the want of
another material cause, was attributed the death of the individual;
but there is no proof that this fluid might not be developed there
after death. We shall now relate a more decided case of death
occasioned by the presence of air in the blood vessels; but here
there is no ground for doubt, because we know the circumstances of
the introduction.

A locksmith, twenty three years of age, had had for five years
a large tumour on the right shoulder and clavicle. His acute
sufferings induced him to enter the hospital to have it removed.

It was necessary in the operation to remove the middle portion
of the clavicle. Thus far the success was complete; but little
blood was lost, the pulse was good and the breathing easy, when
the patient suddenly cried out, _My blood is leaving my body!
I am dead!_ And at the same moment he became stiff, lost his
consciousness, and was covered with a cold sweat. A singular and
rather loud noise was heard in the interior of his chest. The
surgeon thought that he had opened the pleura by removing a portion
of the clavicle, and thus given access to the air and to the blood
to the right side of the thorax. The fingers of an assistant were
immediately thrust into the bottom of the wound, with the view
of stopping the supposed opening in the pleura, and the surgeon
endeavoured to introduce into the thorax the extremity of a sound
of gum elastic. When he thought that he had succeeded, he drew with
his mouth the air which he supposed to be effused in the pleura. He
wished then to proceed to the dressing; and, in order to do this,
he substituted, for the fingers of the pupil which were at the
bottom of the wound, a sponge covered with wax; but the moment the
sponge took the place of the fingers, the same noise that was at
first heard and which had ceased in an instant, was renewed with
more force than before.

The syncope and cold sweat still continued. Water thrown into his
face, made him give some signs of life; but he died a quarter of an
hour after the appearance of the accident I have just described,
and forty five minutes after the commencement of the operation.

The body was examined the next morning. They expected to find the
right pleura open, much blood and air effused into its cavity
and the lungs on that side collapsed. Nothing of the kind was
found. The pleura was whole and there was no effusion in it. The
lungs were as usual; but an opening of half an inch in extent was
discovered in the external jugular vein, at the place where this
vein opens into the subclavian. The cavities of the heart were
large but contained no blood. Bubbles of air were observed in the
vessels of the brain; the other vessels were not examined.

This fact was related to me the same day, by a student who was
present. It was impossible for me not to refer the death in this
instance to the entrance of air into the vessels. The opening in
the vein, the noise that was heard, the suddenness of the death,
the absence of blood in the cavities of the heart, the presence
of air in the vessels of the brain, all sufficiently indicated
it. I suspected that the entrance of air had been favoured by the
state of tension of the parietes of the vein, or by their morbid
alteration, which did not allow them to flatten by atmospheric
pressure. I thought that this phenomenon might be produced at will
on animals by placing them in the same physical circumstances. I
introduced then into the jugular vein of a dog, a sound of gum
elastic, and I directed it towards the heart. It was hardly there
before I heard the air enter the vein, and the animal fell down in
syncope, with the peculiar noise which manifests the presence of
air in the heart. I immediately closed the sound to prevent the
entrance of more air, and the animal gradually recovered, because
the quantity of air introduced had not been in sufficient quantity
to produce its death. I then opened the sound, and immediately the
air rushed in towards the heart, and its entrance was followed by
the same consequences; but, whether from not closing the sound
soon enough, or from the entrance of a greater quantity of air,
the animal died unexpectedly to me. In opening it, I found all the
signs of death from the sudden entrance of air. The right ventricle
was distended with air mixed with a little blood.

Sometimes, without any apparent alteration in the texture of the
veins, its parietes do not flatten under atmospheric pressure;
a simple puncture then is sufficient, as in bleeding, to admit
the air into the vessels. Lieutaud relates two cases in which it
appears that this took place, and several veterinary surgeons have
assured me that they have heard, after bleeding in the jugular
vein, a noise which indicates the entrance of air. Usually the
quantity introduced is too inconsiderable to produce any evident
effects. There has been communicated to me, however, a case
observed by Mr. Bouley, the younger a veterinary surgeon in Paris,
in which the entrance of air was followed by effects similar to
those which we have related.

Mery had long since observed, that, in opening the abdomen of
a dog, and puncturing the vena cava above the origin of the
emulgents, as the vein become emptied of blood, it filled with air,
which went to the right ventricle. Haller also observed that air
entered into the veins of frogs and other cold-blooded animals in
consequence of a wound of some large vessel. He has shown that it
was from this source that was derived that which Redi, Caldesi, and
Morgagni saw circulating in the vessels of these animals, since
it is not observed, when the necessary precautions are taken to
prevent its introduction.

Nysten has made a great number of experiments upon the injection
of elastic fluids into the veins, and the results which he has
obtained accord perfectly with those which we have observed. He is
not satisfied with injecting atmospheric air, he has introduced in
the same way a great number of other gases. He has remarked, that
among the gases not deleterious he can introduce, without causing
death, a much greater quantity if these gases are easily dissolved
in the blood.

We cannot follow him in the detail of these experiments; we shall
only relate a result relative to the colouring of the blood in
the lungs. He has observed, that by injecting air into the vein,
so slow as not to produce the death of the animal, the colouring
of the arterial blood is rendered imperfect. He is satisfied, he
says, that it is not owing to the embarrassment of the lungs. The
injection of oxygen does not alter this colouring. The injection
of azote completely prevents it; that of the oxide of carbon does
not produce any change in it. I give these results from his work; I
have not had occasion to verify them myself.

[67] When air is introduced into the vena portæ, there is not only
no ill effect at the moment of injection, but there usually follows
no apparent effect on the animal. It is not the same when air is
injected into the veins of the general system, with so much care
as not to produce instantaneous death by the dilatation of the
heart. The effects do not then appear till a long time after the
injection; but they are wholly different from the primary effects
which we have described.

These consecutive symptoms from the entrance of air into the veins
are, as Nysten has remarked, the result of an obstruction of the
lungs produced by the accumulation of air in the last divisions
of the pulmonary artery. The embarrassment in respiration often
appears at the end of half a day, it becomes greater and greater,
the bronchiæ are filled with a viscid fluid; and the animal usually
dies on the third or fourth day. On examination of the body, no
air is found in the heart or the vessels; but the lungs, instead
of being pink-coloured, are greyish, tinged with brown, and loaded
with frothy blood and mucus.

Boerhaave thought, that death which follows the injection of
air into the veins was always owing, as it is in this case, to
the presence of the air, which offers, in the small vessels, a
mechanical obstacle to the passage of the venous blood.