Part 30

For the same reason that all the blood of the pulmonary artery goes through the lungs, the foramen ovale is closed; in fact, this foramen is so arranged at birth, that its valves approximate so as to cross, as it were; so that when they are pressed against each other, the communication of the auricles is really closed. Now the red blood entering the left auricle by the pulmonary veins, pushes the valve of the foramen ovale corresponding to this auricle, against the other, and consequently opposes the blood of the vena cava inferior that endeavours to enter there. This blood flows back to the right auricle. Now when this contracts to drive the blood into the ventricle, far from forcing it through the foramen ovale, it necessarily brings the two valves against each other, and obliterates it. By examining with care the state of the heart of the fœtus, it is evident that when the blood enters the left auricle by the pulmonary veins, the right by the venæ cavæ and the valves are crossed, it is impossible that the blood can pass them either in contraction or dilatation.

Though the foramen ovale may be open at birth, still the black blood ceases to pass through it; I say further, oftentimes this foramen remains open during the whole of life. Many authors have related examples of this. I have seen a great number, though this assertion may appear extravagant at first. It is impossible from the arrangement of its two valves, for the blood to pass through it. When the two auricles contract at the same time, the blood which is forced by them from without within, brings the valves together, and thus itself creates an obstacle to its passage. In the greatest number of cases, the adhesion of the two valves crossed, is extremely weak; they are rather in contact than united; so that by forcing between them the handle of a scalpel, they are easily separated and hardly any traces of rupture are found. If they were arranged so that the blood could insinuate itself between them, it would soon separate them and re-establish the communication. Authors need no longer attempt to explain, how life is supported when the foramen ovale is open; it is the same as if it was closed, no more blood passes through it.

The obliteration of the foramen ovale, and the cessation of the passage of the blood through its opening, are, as we see, phenomena to a certain degree mechanical. The vital laws perform also, without doubt, their part on this occasion. Who knows if the sensibility of the left auricle, stimulated and modified anew by the red blood, does not repel the black which tries to enter it by the foramen ovale? We see every day in the economy, fluids passing at the side of openings, without entering them, though they may be wide, for the sole reason that their sensibility is not in relation with these fluids. Why does the trachea convulsively reject all fluids and solids? why does the air alone enter it? Why does not the blood enter the thoracic duct, which is often furnished with a valve, as I have observed, incapable of opposing its passage, and sometimes even has none? Why does the urethra repel the urine in coition? It is a fault of all authors that they seek only for mechanical causes in all the phenomena of the circulation. Without doubt the course of the blood is a mechanical phenomenon; but the laws that govern this course are vital; it is the same as a bone that is moved by muscular contraction; the effect is the mechanism of the lever; the cause is vital.

The blood no longer passing through the ductus arteriosus, this closes immediately by its contractility of texture; it becomes a kind of ligament, which fixes to a certain degree the aorta and pulmonary artery in their respective position. As to the obliteration of the foramen ovale, it does not arise from this contractility; this obliteration is not made by a contraction, but by a real agglutination of the two valves, between which it is obliquely situated at birth. This agglutination appears to be the effect of a pressure that is made in an opposite direction, upon the partition between the auricles, by the blood that each contains. In fact their fibres are so arranged that they contract from without within; now by contracting thus, they press from each side the blood against the partition, and consequently the two valves against each other. Now this agglutination sometimes does not take place, whilst the contractility is always exerted when the parts in which it exists cease to be distended; the ductus arteriosus is uniformly obliterated.

At the same time that the ductus arteriosus and foramen ovale cease to transmit blood at birth, this fluid is stopt in the umbilical artery and vein. Why does the blood cease to flow in this artery, though its diameter continues very large at birth? The principal cause appears to me to be the nature of the red blood, which is no longer in relation with the sensibility of this artery. A proof of this is, that if some time after the fœtus has breathed, respiration is stopt, and the black blood consequently returns, the umbilical arteries begin to pulsate, and if the ligature is loosened, they pour out considerable blood. Baudelocque has frequently observed this.

In general, when respiration is well established, the blood no longer flows by the umbilical artery, the ligature of the cord is then useless. On the other hand, when this function is badly performed, there is reason to fear hemorrhage of this artery. I confess, however, that there may be other causes for this interruption of the passage of the red blood. These four things, 1st, the cessation of the entrance of the blood into the umbilical vein; 2d, interruption of the passage of that of the inferior vena cava by the foramen ovale; 3d, of that of the pulmonary artery by the ductus arteriosus; 4th, of that of the descending aorta by the umbilical artery; these four things, I say, the three last especially, appear to depend upon a cause that we do not yet understand. The change of the relation of the organic sensibility with the nature of the blood, is perhaps only accessory, since, as I have observed, it is less this property than the action of the heart itself, which is the cause of the circulation in the trunks. This subject deserves the most attentive examination of physiologists.

Respiration being once well established, the lungs are in opposition to the whole body; it sends blood to all the parts, and they all send it to the lungs. The boundary is then rigourously established between the system with black blood and that with red, and things then go on as we have before described.

After birth the vascular system with red blood predominates for some time by its greater development and its more numerous branches, in fact the red blood enters more parts then than it does afterwards. It is sufficient to dissect living animals of different ages, to be convinced of the greater quantity of blood in young animals, that the system contains, of which we are treating; so that, as I have said elsewhere, the two opposite ages of life exhibit an inverse arrangement as it respects the fluids and solids. The first are much more abundant towards the period of conception. The second always predominate more towards the last age.

The predominance of the system with red blood remains evident to the end of the period of growth. We see the necessity of this predominance to distribute to all the parts the materials of their nutrition and growth; in fact, in the adult the arteries contain only what is destined to the first. In the infant, they contain moreover what is destined to the second. Hence the caliber of the arteries is proportionably larger than afterwards, in order to contain more fluid. Injections demonstrate this; and on this account small subjects are not less favourable for the study of the arteries, than of that of the nerves. These vessels are more prominent in them; only the surrounding parts being less developed, we cannot see the connexions so well.

In proportion as the infant advances in age, the equilibrium is gradually established in the system with red blood. In the head, the facial arteries are more evident, and come gradually in their development to the level of the cerebral. In the thorax, the thymus diminishing as the lungs increase, their nutritive arteries follow an inverse order; the bronchials dilate and the thymic contract. In the abdomen less blood goes to the capsular arteries; but most of the others receive as much of it. The pelvis and the inferior extremities have more of it, and their development is proportionably evident.

III. _State of the Vascular System with Red Blood after growth._

It is about the period of puberty that the increase in height ceases; the increase in thickness continues always. The genital parts, hitherto without influence, seem to be then a centre of more active vitality than most of the other organs. The portion of the system with red blood that belongs to them, then becomes greater. The first effect that results from it is the secretion of semen, and a general impulse of the individual towards new tastes and desires, towards those relative to the propagation of the species.

Another phenomenon is soon the consequence of this. As the lungs are connected in an intimate, though unknown manner, with the genital parts, they acquire also a predominance with them. Their vital energy is increased, and then begins the period of the affections of this viscus; then, the cause that would in the adult produce a gastric affection, brings on a pulmonary one.

It is truly only at this period, that the predominance of the superior parts, of the head especially, ceases entirely. Thus whilst in infancy the nose is frequently the seat of hemorrhage, in youth it takes place particularly from the lungs. We may consider the increase of the energy of the lungs, which happens shortly after puberty, as the termination of the predominance of the superior parts. The cutaneous eruptions of the cranium, tinea capitis, &c. cease to be as frequent. Convulsions, and all the diseases that arise from the extreme susceptibility of the brain, become also more rare, and seem to give place to a great number of acute pulmonary affections.

It is towards this period, that is, some time after the end of the increase in height, that the diseases that are considered as the product of an arterial plethora, begin especially to manifest themselves; this may be said to be their age, and it arises from the following cause; as the blood contains before puberty, not only the materials of nutrition, but also those of growth, and whilst this continued the whole is expended in the system with red blood. But when the parts cease to increase in length, if this system still continues to receive the materials of growth, a true arterial plethora takes place. About the end of growth generally, some affections appear that indicate a predominance of the blood; as this is however under the influence of temperament, of the mode of life hitherto led, of the season and a thousand other causes, which, making the phenomena of the animal economy vary, rarely permit us to establish exclusive general principles. Thus all that is said upon the disposition to different diseases, in the different ages, &c. is subject to many exceptions.

The predominance of the lungs is gradually lost; the equilibrium is established among all the organs, which, hitherto had each performed a part more or less conspicuous in the phenomena relative to the different ages. As the system with red blood is uniformly, in every part, in proportion to its growth, to which it especially contributes, the equilibrium is in that way established between the different parts at twenty-six or thirty years of age; all the arteries have a proportional size, analogous to what they will always have afterwards. Whilst until then, some predominated, according to the predominance of the growth of the organs to which they are sent.

Towards the fortieth year, the gastric viscera seem to acquire a more decided vital activity; but this activity has no influence upon the size of the arteries that are distributed to these viscera.

Though the growth in height may end about the sixteenth or seventeenth year, that in thickness uniformly continues; so that the internal viscera still grow, and their arteries consequently enlarge, until the last growth ceases. This phenomenon has constantly struck me, in comparing arteries injected in subjects from sixteen to twenty years, with those in subjects beyond thirty-six or forty. In the last they are uniformly larger. It is this difference that first gave me the idea of distinguishing growth, into that in height, and that in thickness. For the development of the arteries is the constant index of the state of the growth of the organs. The period of the cessation of growth in thickness is then remarkable, 1st, by the cessation of the increase of the caliber of the arteries; 2d, by the general equilibrium that is established in their development.

As the arteries grow in the years that succeed the end of the growth of the body, they increase in compactness and thickness. Their fibres become more evident; their elasticity increases; their pliability is lessened; hence why the age of the adult is that of aneurisms. Observe that the density of the arteries follows, in its augmentation, the same proportion as the fleshy fibres of the heart; so that as this is more able to send the blood with force, these are more able to resist it.

IV. _State of the Vascular System with Red Blood during old age._

In the last years, the system with red blood is remarkable for the following phenomena.

The number of the arterial ramifications is much diminished. As the heart loses its energy, it sends less blood, and with less force. The general vibration that it produces in the whole arterial tree, is less felt at the extremities of this tree. The small vessels that form these extremities gradually contract, are obliterated and become so many little ligaments. Hence why, when the periosteum is separated from the bone, the dura mater from the internal surface of the cranium, only a few drops of blood escape; why the skin, having hardened like horn, no longer exhibits the rosy tint of the preceding ages, especially of youth; why the section of a bone does not furnish hardly any blood, whilst it was so abundant in the fœtus; why the mucous surfaces look pale, the muscles have a dull colour, &c. All anatomists know that injections succeed less in proportion, as the subjects are more advanced in years; that in extreme old age the trunks alone are filled; that the fluids never enter the ramifications; that it is the reverse in young subjects; that even coarse injections oftentimes so fill the ramifications, as to render dissection difficult. I have dissected many old living animals; and the small quantity of blood their vessels contain compared with those of young animals is very remarkable. The general proposition that I have established, viz. that the solids are constantly acquiring the predominance, is perfectly true. This obliteration of the small vessels is remarkable even upon the parietes of the great vessels; we see it in the dead body; I have observed it in the living.

The less quantity of red blood that is found proportionably in old age, is referable especially to the state of nutrition, which is merely nothing when compared with that of infancy. Observe also, that united with the weakness of the motion that animates the blood, it is a cause of the small degree of excitement which the parts have in old age. In fact the use of the circulation is not only to carry to the different parts the materials of the secretions, of exhalations, nutrition, &c. we shall see that it keeps them also in a state of constant excitement by the shock it gives them at its entrance, a shock, the principle of which is evidently in the heart. Now this shock is in a ratio compounded, 1st, of the quantity of the fluid; 2d, of the force with which it is sent. In both respects, the excitement constantly diminishes, as age advances. Observe also that all the functions of the infant, both organic and animal, are characterized by a vivacity and impetuosity that form a remarkable contrast with the slowness and want of energy of those of old people.

The arterial texture always becomes more and more condensed as age advances. The layers that form the fibres of the peculiar membrane become drier, if I may be allowed the expression.

I have said that the internal membrane is very often the seat of a kind of peculiar ossification, which has hardly any influence upon the circulation, except when it is seated at the origin of the aorta.

The caliber of the arteries does not dilate in old age. There is scarcely any except the arch of the aorta, which constantly undergoes an enlargement more or less considerable, which is always without rupture of the fibres, consequently supposes an extensibility of these fibres, and undoubtedly depends upon the habitual and direct impulse that the blood exerts against the concave side of this curvature. I have often examined to see if there was a similar dilatation at those places in the arteries where the curves are very evident, in the internal carotid, for example, at the place where it passes through the carotid foramen; I have not discovered any.

In the last periods, the pulse is remarkable for its extreme slowness; a phenomenon opposite to that of infancy, in which the blood moves with great quickness. These two opposite facts are, after what we have said, foreign to the arteries. They indicate only the state of the forces of the heart, which is the agent of the general impulse of the red blood.

It is the same of the pulse in the last periods of life. It is not a real pulsation of the arteries; it is a kind of undulation, of weak oscillatory motion, and the more obscure, as life is more feeble. Now I am convinced that the heart alone is the agent of this undulation; I am convinced of it by the following very simple experiment. I have laid bare in many dogs, on one hand the carotid, on the other the heart by a section of one side of the thorax, made in such a manner that the other can still perform respiration. By placing the finger upon the artery, I observed that as long as the heart beat by a sudden impulse, that the pulse was kept up as usual, that it was even accelerated, because the contact of the air increased the quickness of the contractions of the heart; but at the end of a little time, this organ began to be weakened in its motions, then it contracted by a kind of general tremor of its fibres. In proportion as the weakness of the motions of the heart increased, the pulse was successively weakened. Then when the tremor extended to all its fibres, the pulsation of the artery changed to a kind of undulation, of feeble oscillation, the precursor of the cessation of all motion.

I shall observe, under the system of the muscles of organic life, that the heart has many kinds of contraction. The principal are, 1st, that which it ordinarily has, in which there is a contraction and a dilatation that succeed suddenly and regularly; 2d, that in which these two motions, retaining their natural character, are irregularly connected; 3d, those in which the fibres only oscillate, and by which the cardiac cavities a little contracted, communicate to the blood a less sudden shock, a general tremor, an undulation, &c. Now with each kind of motion of the heart, there is a peculiar pulse that corresponds. It is easy to be convinced of this upon living animals.

I am astonished that authors who have disputed so much upon the cause of this phenomenon, have not thought of having recourse to experiment to elucidate the question. There are undoubtedly many modifications in the pulse, whose coincidence with the motions of the heart could not be perceived; but that of the slow and frequent pulse, the strong and weak, the intermittent, undulatory, &c. can be immediately discovered, by laying the heart bare and placing the finger at the same time upon the artery. We see then uniformly, during the moments that precede death, that whatever may be the modification of the arterial pulsation, there is always an analogous modification in the motions of the heart; this certainly would not be the case, if the pulse depended especially upon the vital contraction of the arteries. I have had occasion to make these experiments many times, either directly for this object, or with others in view; I have seen the motion of the heart always correspond with that of the arteries. In general the theory of the pulse requires as I have said, new researches; but I have facts enough upon this point to be convinced that the varieties it undergoes in the different ages, as under other circumstances, depend almost exclusively upon the heart, which produces in particular this kind of undulation, of oscillatory motion which is between the pulsation of the natural state and the complete cessation of this pulsation.

V. _Accidental development of the System with Red Blood._

I shall speak under the organic muscles, of the accidental development of the left portion of the heart. As to the arteries, new ones are never formed; but oftentimes, those that do exist acquire a remarkable size; this depends on two causes, 1st, on an obstruction to the course of the blood; 2d, on the growth of any tumour.

1st. The dilatation of the arteries by an obstruction to the circulation, is evident in the ligature of aneurismatic arteries, in the spontaneous cure of aneurisms, a phenomenon of which within a few years a great number of examples has been published, &c. Then, sometimes the great collaterals increase in size, sometimes their caliber remains the same, and it is by the ramifications that the communications are made. As the branches dilate, their thickness increases in proportion with their breadth; at least I have twice observed this fact, which is analogous to that which the left ventricle presents when it becomes aneurismatic.

2d. All tumours do not produce a dilatation of the arteries; we see this dilatation in cancers, in those of the breast, of the womb, &c. in osteo-sarcosis or spina ventosa, in the different fungi, &c. In general, most tumours that give great pain to the patients exhibit this phenomenon. We should say even that pain in a part is sufficient to attract there habitually more blood, and dilate the arteries; we know that in the operation for lithotomy, when the patients have previously suffered much, hemorrhage is often more to be feared.

After long and copious secretions or exhalations, I have not observed that the arteries were more dilated in the glands or around the exhalant organs. How large soever the cysts may be, their parietes never contain arteries proportioned to those that are developed in cancerous tumours. The cerebral in hydrocephalus, the mediastinal, intercostals, &c. in hydro-thorax, the mesenteric, the lumbar, the stomachic, the epigastric, &c. in ascites, the spermatic in hydrocele, the renal in diabetes, the branches that go to the parotids after a long salivation, retain their ordinary size, and under some circumstances they become even smaller.

When the arteries dilate in tumours, do their parietes thicken in proportion, as in the preceding case? I have no data, from which I could determine this point.

VASCULAR SYSTEM

WITH BLACK BLOOD.

The red blood circulates in a single system, the branches of which every where communicate. The black blood on the contrary is contained in two separate systems, which have nothing in common but the form, and which are, 1st, the general system; 2d, the abdominal. We shall now examine the first, and afterwards the second.