General Anatomy, Applied to Physiology and Medicine, Vol. 1 (of 3)

by Xavier Bichat

The fœtus finds at birth that all surrounding objects are the causes of great excitement; the cutaneous surface, all the origins of the mucous, are strongly stimulated. The sensations they experience are even painful, because the difference is very great between the waters of the amnios and the bodies with which the fœtus comes in contact at birth, and every abrupt change in the sensations is painful. Habit soon familiarizes this sensation; but it is not less real at birth, and it may be said that this moment is as painful for the infant as the mother. Now, as every lively sensation is generally accompanied with great motions a general agitation succeeds the impression that the fœtus perceives from without; all the muscles move, the intercostals and the diaphragm like the others. The air which already filled the mouth and wind-pipe, then enters the lungs, and there colours the blood red, then it is alternately expired and inspired until death. The first inspiration then is, in this point of view, a phenomenon analogous to all the motions that the change of external excitement suddenly produces at birth in the voluntary muscles of the fœtus.

The respiratory motion is, however, too important, since it commences a new kind of relation between the organs, to depend exclusively upon this cause. I presume that an unknown principle, a kind of instinct, induces the fœtus at the moment of birth, to contract the intercostals and diaphragm. This instinct, which I do not understand, and of which I cannot give the least idea, is the same that makes the infant the moment it comes from its mother's womb, contract its lips, as if to nurse. We certainly cannot say that this motion is an effect of the very acute external impressions that it feels; these impressions produce agitations, irregular motions, as if to get rid of these impressions, and not a uniform motion evidently directed towards a determinate object. If we examine all animals separately at the instant of their birth, we shall see that every one performs particular motions, directed by its instinct. The small quadrupeds seek the breast of their mother; the gallinaceous animals the grain that is to nourish them; the small carnivorous birds immediately open their bills, as if to receive the prey the mother is afterwards to bring to them in the nest, &c.

In general, it is essential to distinguish accurately the motions, which, at the instant of birth, arise from new excitements that the body of the fœtus receives, from those which are the result of a kind of instinct, of a cause of which we are ignorant. I believe that the respiratory motion belongs at the same time to the two causes, and more especially perhaps to the last.

I pass now to the mechanical revolutions of the course of the blood. At the instant the lungs change to red the black blood that enters them by the pulmonary arteries, they receive all that which before passed through the ductus arteriosus; this ceases to transmit any to the aorta, though, however, it often remains still more or less dilated; for at birth it is hardly ever entirely obliterated; this contraction varies singularly at this period. Why does the blood then cease to flow there? As the aliments do not enter the ductus choledochus, the lacteal or pancreatic ducts, though they pass their orifices; so undoubtedly this takes place, because the kind of sensibility of the ductus arteriosus repels the new venous blood of the fœtus, which comes no longer from the placenta, because that which the lungs have reddened will not mix with it. We cannot certainly give any mechanical reason for its not passing; it really does not, and it evidently depends upon the vital laws. Besides, the motion of which the lungs become the seat, the dilatation, and especially the new excitement that the external air produces there, by rendering considerably more active the capillary circulation, facilitate that of the two pulmonary trunks, and give the blood a tendency to pass there rather than through the ductus arteriosus; it is in this way that the lungs attract, as I have said, the blood from the pulmonary artery. Does not the great irritation, of which certain tumours are the seat, draw there more of this fluid? Is it not on this account that the arteries of these tumours dilate and acquire a double or even treble caliber? What takes place in these tumours in a gradual manner, happens suddenly to the blood that still passes by the ductus arteriosus at birth, and which was very much diminished, as I have said, by the successive contraction of this canal.

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.