Part 36

1st. The liver exists in all classes of animals. In those even in which most of the other essential viscera are very imperfect, it is well developed. 2d. Most of the passions affect it particularly, many of them have an exclusive effect upon it, whilst a great number of the other glands hardly perceive them at all. 3d. In diseases, it takes as evident a part as the first viscera in the economy. In many nervous affections, in hypochondria, melancholy, &c. it has a great influence compared to other glands. We know how easily its functions are deranged. It has undoubtedly no connexion with some affections called bilious, and which are seated exclusively in the stomach, but it certainly has a part in most of them. Since there is no doubt that the jaundice depends wholly upon a serious affection of this viscus, we ought certainly to conclude that the yellow tinge of the face in many of these affections, arises from a cause existing in this viscus, and which is not sufficiently powerful to produce jaundice. Whether in order to produce this tinge, the bile circulates or not with the blood, is of no consequence; it is incontestible that it is occasioned by affections of the liver; now the numerous cases in which it takes place, prove how much this viscus is often affected; there is certainly no gland in the animal economy so frequently. 4th. Shall I speak of organic affections? compare in the examination of bodies, those of the liver, with those of all the other organs of the same class, and you will see that there is no one equal to it in this respect; the kidney approaches it, in the frequency of the alteration of its texture, but it is far from being equal to it. 5th. Who does not know the influence of the liver upon temperaments? Who does not know that its predominance gives to the external appearance, the functions, the passions, the character even, a peculiar shade which the ancients have noticed, and which modern observations have confirmed? Now see if the other glands have a similar influence in the economy. 6th. The liver is, with the heart and the brain, the organ that is first formed; it precedes all the other organs in its development; it is incomparably superior, in this respect, to all the glands.

From all these considerations, and from many others that I might add, we may conclude, I think, that the unknown part which the liver performs in the animal economy, besides the secretion of bile, is among the most important. The study of this part, is one of the points most worthy of arresting the attention of physiologists.

It has been said latterly, that the liver corresponded to the lungs in their functions of removing from the blood its hydrogen and carbon. I know not how this fact can be proved by experiment; but I am positive that the liver does not turn the black blood of the abdominal system into red. 1st. The blood of the right auricle is of the same colour as that of the vena cava inferior; now if the blood went red from the hepatic veins, it would certainly give a brighter tinge to that of the auricle. 2d. Having opened the abdomen and thorax of a dog, I tied with a curved needle the vena cava at its entrance into the heart and above the kidney, then by detaching the liver from behind, I cut the portion intercepted between the two ligatures, and where the hepatic veins opened; the blood came out as black as that of the rest of the system. 3d. Tear out the liver of a living animal, examine immediately its veins, you will see that they contain a blood analogous to that of the others. 4th. This viscus, cut in slices in a living animal, pours out behind an analogous fluid, except some small red streams furnished by the last small branches of the hepatic artery; this is wholly different in the same experiment made upon the lungs.

If the black abdominal blood receives any modifications of its nature in the liver, they certainly have no influence upon its colour, its consistence, or sensible qualities.

The general opinion is that the black abdominal blood serves for the secretion of bile, and that the hepatic artery is only destined to nourish the liver; this is what Haller has adopted; I have also admitted it; but I am far from considering it as clearly demonstrated as it has generally been thought to be; the following observations prove, that we ought to consider it as an hypothesis somewhat uncertain.

1st. It is said that the hepatic blood, blacker, more oily, impregnated with the vapours of the excrements, of a bitter taste even, approaches nearer the nature of bile than the arterial blood, and that it is consequently more proper to form it. I do not know whether this blood has been analyzed comparatively; but I have certainly not found any difference in its external attributes; I did think that in an experiment I observed fatty drops swimming in it; different experiments have convinced me that it was an error. I doubt whether it could ever be demonstrated that the alkaline particles of aliments and of excrements pass into the vena porta; this passage is a gratuitous supposition. 2d. It is said that the volume of the liver is considerable compared to the hepatic artery; this is true; but it is not with the size of this viscus that we should compare that of this artery, to know if it furnishes the materials of secretion, since we have seen that it is impossible that the whole substance of the liver should be destined to secrete bile; it is with the biliary ducts and their reservoir, that we should make the comparison; now this artery is exactly proportioned to these ducts; there is between them nearly the same relation as between the renal artery and the ureter; on the contrary, the biliary ducts are manifestly disproportioned to the vena porta. 3d. It is said that the slow motion in this vein, is favourable to the secretion of bile. But upon what positive data is this assertion founded? Why is slowness of motion more necessary for this secretion than for others? 4th. It is said that the hepatic artery having been tied, the secretion of bile continued. But when we know the relation of parts, the least reflection is sufficient to convince us, that a ligature of this kind cannot be made without producing a derangement that will prevent us from distinguishing any thing. I attempted it once, but could not finish it; I was almost persuaded of it before. 5th. It is said that the black blood is more proper to furnish the materials of the bile than the red. But what is the reason of it? is it because this blood contains more carbon and hydrogen? But it is then the black blood that furnishes the fat also; now all anatomists are agreed, that it is exhaled from the exhalant extremities of the arteries; the same is true of the marrow, the wax, and in general of all the oily fluids. 6th. A fine injection, made in the hepatic portion of the abdominal system with black blood, passes into the biliary vessels. But a similar passage takes place in an injection from the hepatic artery. 7th. It is said that the black abdominal blood in the spleen has qualities essential to the bile. But the secretion of this fluid can evidently take place without the spleen; many experiments prove this. 8th. It is said that at the instant the vena porta is tied, bile ceases to be secreted; it is undoubtedly less difficult to tie the trunk of this vein below the duodenum than the hepatic artery. How can we examine what is going on in the liver? Do we judge by the fluid flowing from the hepatic duct? But open the duodenum, and you will not very often see the bile running out at the opening of the ductus choledochus, undoubtedly because the air contracts and irritates this duct. This phenomenon, observed after a ligature is applied, is not then conclusive; moreover there does flow towards the time of digestion but too little bile by the ductus choledochus, to be able to estimate it. In fine, what inference can be drawn from an animal whose abdomen is open?

These different reflections prove, I think, that we have not sufficiently direct proofs, to decide whether the secretion of bile is from the abdominal black blood or the red. I do not attribute this function more to one than the other; I say that these things should be subjected to a new examination, and that this example is a proof that the opinions most generally received in physiology, those consecrated by the assent of all celebrated authors, often rest upon very uncertain foundations. We are yet far from the time when this science will be only a series of facts rigorously deduced from each other.

The hepatic artery has been said to resemble the bronchial, and the hepatic vena porta the pulmonary artery; this is true in the general arrangement; but what is the proof of it as it regards the functions? On the contrary, I have proved above that those of the two last vessels are not similar. Let us wait, before deciding, for further and positive researches; let us doubt till then; let us not attribute the secretion of bile to the hepatic artery, nor the vena porta, nor to them unitedly. Certainly it is by one of these three means; but which? what vessel furnishes the secretion of bile? what part does the black abdominal blood perform in the liver, if it is not from it that this fluid is secreted? what, in fine, is the function of the hepatic artery, if it is not connected with this secretion? These are questions to be resolved.

Physicians have also hazarded opinions upon the influence of the black abdominal blood in diseases. Undoubtedly the expression, _vena portarum, porta malorum_, contains a very true meaning; but certainly in the present state of our knowledge, it is, in a strict sense, only a play upon words. If we would express by it the frequency of affections of the liver, it is without doubt just; but if it is employed to express the influence of the vena porta in diseases, it is vague and does not rest upon any positive fact. The more we open dead bodies, the more we shall be convinced, I think, of the necessity of a precise and accurate language, freed from all these ingenious, hypothetical ideas, which do honour, it is true, to their author, but which retard science, by introducing into it a manner of seeing hypothetically, and contrary to the spirit of observation.

_Remarks upon the course of the Bile._

Though this question may be to a certain degree foreign to my object, yet as the black abdominal blood has perhaps a real influence upon the secretion of the bile, as my experiments upon this point determine with precision the course of this fluid, I do not think it useless to relate them here. All that is known further upon the uses, mechanism, &c. of this secretion is to be found in works of physiology, to which I refer.

There has been much discussion to ascertain if there was cystic and hepatic bile, if one was of a different nature from the other, if their quantity increased or varied, &c. Contrary and even opposite opinions have been supported by numerous experiments made upon living animals, as Haller has observed. These experiments, though at first view contradictory, are not so, however, as I was convinced by repeating them at different periods of digestion and during the abstinence of the animal; it had not been done with precision. The following is what I have observed in dogs, which I have used in my experiments.

1st. During abstinence, the stomach and small intestines being empty, we find the bile in the ductus hepaticus and ductus choledochus yellowish and clear; the surface of the duodenum and jejunum tinged by bile which has the same appearance; the gall-bladder much distended by a greenish, bitter bile, much deeper coloured and more abundant if the abstinence has been long. 2d. During digestion in the stomach, which may be prolonged for a length of time, by giving to a dog large pieces of meat, which he swallows without masticating, things are nearly in the same state. 3d. At the beginning of the intestinal digestion, we find the bile of the hepatic duct always yellowish, that of the ductus choledochus deeper coloured, the gall-bladder less full and its bile already becoming clearer. 4th. At the end of digestion and immediately after, the bile of the hepatic duct, of the ductus choledochus, that in the gall-bladder, and that which is found upon the duodenum, are of precisely the same colour as the common hepatic bile, that is, of a clear yellow, and a little bitter. The gall-bladder is about half full; it is flaccid, not contracted.

These observations, repeated a great number of times, evidently prove that this, during abstinence and digestion, is the manner in which the flow of bile takes place; 1st, it appears that at all times the liver secretes a certain quantity, which is increased during digestion; 2d, that which is furnished during abstinence is divided between the intestine that is always coloured with it, and the gall-bladder which retains it, without pouring out any portion of it by the cystic duct, and in which, thus retained, it acquires an acrid character and a deep colour, necessary, no doubt, to digestion which is to follow. 3d. When the aliments, having been digested by the stomach, pass into the duodenum, then all the hepatic bile, which was before divided, flows into the intestine, and even in greater abundance. On the other hand, the gall-bladder pours also that which it contains upon the alimentary mass, which is then completely penetrated with it. 4th. After intestinal digestion, the hepatic bile diminishes, and a part begins to flow into the duodenum, and a part to flow back into the gall-bladder, in which, if then examined, it is found clear and in small quantity, because it has had neither time to be coloured or accumulate.

There is then this difference between the two biles, that the hepatic flows almost in a continued manner into the intestine, and that the cystic flows back, except during digestion, into the gall-bladder, and flows, during this function, towards the duodenum; or rather it is the same fluid, of which a part always preserves the same character that it had at its exit from the liver, and the other assumes a different one in the gall-bladder. The diversity of colour in the cystic bile, according as it has been retained long or not, has much analogy to the colour of the urine, which is found more or less deep coloured, as it has been for a longer or shorter time in the bladder.

As to the course of the bile in relation to the stomach, I believe that this viscus contains a certain quantity of it at all times. When empty, we find there a mixture of gastric juices and mucus more or less abundant, sometimes mixed with small bubbles of hydrogen, which burn when brought in contact with flame, and almost always tinged with a yellowish colour from the bile that has flowed up through the pylorus. Haller says that this reflux of bile into the stomach does not always happen; Morgagni says that it always does in men. I have never opened a dog, in whom it has not been seen when the stomach was empty, especially if it had been so for some time. Human dead bodies are not proper to decide this question, because the kind of disease alters almost inevitably the course, the nature, and even the colour of the bile. I shall say in another volume what conclusion we should draw from this, as it respects bilious vomitings.

In a state of fulness, it has sometimes appeared to me impossible to estimate the reflux of the bile; in other states, between the alimentary mass and the parietes of the stomach, I have seen yellowish, gastric fluids; but this mass itself never has this colour.

The bile that flows into the stomach has always appeared to me to be hepatic bile, from its light colour. I think that I have opened a sufficient number of living animals to convince me, that this bile is hardly ever found very green, and that it acquires this colour from the gall-bladder; and that it is this that is brought up by vomiting in some affections. The reflux of this bile appears to be an effect of the affection itself. This observation agrees with that made above, viz. that the hepatic bile alone flows into the duodenum in abstinence. It alone can then, as we may be convinced, flow into the stomach. During intestinal digestion, in which the cystic bile flows, it is evident, that the aliments going continually out of the pylorus, prevent it from passing there and entering the stomach; that which we find during fulness, was there then, or entered there before the peristaltic motion had begun to evacuate this organ.

When we open the gall-bladder in a dead body, we see that the bile there exhibits, according to its diseases, a variety of shades of colour, from that which is black as ink to a kind of transparent fluid. Ought we then to be astonished, if the vomitings in which the cystic bile is brought up, that has flowed into the stomach against the ordinary course of things, should contain matters of such various colours?

_Development._

In the fœtus, the system of black abdominal blood is not insulated; it becomes a part of the two others, by means of the ductus venosus. There is then truly but one vascular system in the fœtus, whilst after birth, there are three separate ones, two with black blood and one with red.

In the fœtus, it is especially with the umbilical vein that the abdominal system with black blood is continued. The liver is a centre, in which both arrive from two different sides, and in which they unite, in a common trunk. The two columns of blood that they circulate, do not meet directly; their course forms a very remarkable angle.

When we examine attentively the orifice of the ductus venosus in the trunk, made by the union of these two veins, we see that it presents itself naturally to the blood of the umbilical vein; that that of the vena porta, on the contrary, cannot enter there. In fact, there is a little fold in the form of a valve, less evident, it is true, than many others, but yet existing. This fold is only a kind of projection, placed between the end of the vena porta and the ductus venosus, and which contracts the orifice of this, so that it is evidently narrower than the caliber of its own canal. The blood coming from the vena porta and passing at the side of this fold, presses it against the orifice, and thus forms an obstacle; that coming from the umbilical vein, falling, on the contrary, perpendicularly on this orifice, removes this fold, and enters the canal.

It hence follows that the ductus venosus is evidently destined to carry to the vena cava the residue of the blood of the umbilical vein; I say the residue; in fact, as this vein is very large and the ductus small in proportion to it, it is evident that the greatest part of the blood penetrates the liver, by the different ramifications that enter its substance.

The abdominal vascular system is less developed in the fœtus than afterwards; it consequently carries less blood to the liver; this is the same arrangement as in all the other veins. I would observe, that the small quantity, however, which the liver receives in this way, is more than compensated by that of the umbilical vein. This viscus is, then, habitually entered in the fœtus, by a greater quantity of fluid than at any of the other ages. Hence, 1st, why its nutrition is so developed and its size so great; 2d, why it is, in proportion to its size, heavier than in the after ages; 3d, why when we cut it in slices, there flows out a greater quantity of blood; 4th, why, when we dry slices of the liver of a fœtus, of the same thickness as others taken from the liver of an adult, and especially of an old person, they are reduced to a less size.

The disproportion of the size of the liver of the fœtus is more evident, the sooner it is examined after conception; this is the same as with the brain. As the fœtus advances towards birth, the liver approximates in its proportions to the other organs, that which it will have in the adult. From the observations of Portal, it is especially till the seventh month, that the liver is predominant. This circumstance appears to arise from this, that the umbilical vein transmits as much more blood in proportion to the fœtus, as it is less advanced in age.

At this age, the blood of the umbilical vein and that of the vena porta evidently mix, at least in a great measure, in the common trunk. Is their nature analogous? There is no experimental knowledge upon this point. But Baudelocque has many times observed that that of the umbilical vein is redder, and even approximates the nature of arterial blood. I have not accurately observed this fact in any animals except guinea pigs, in whom the want of transparency in the cord does not allow us to see a great difference in the blood of the arteries and of the umbilical vein; but this difference can be in fact more evident in man; now, in this case, the umbilical blood appears to lose this redness in the liver, for very certainly it is uniform beyond this viscus in the circulation of the fœtus, as I have often ascertained.

At the period of birth, the blood ceasing to come by the umbilical vein, the liver becomes only the termination of the black abdominal blood. Then a kind of revolution takes place in this viscus. The different tubes that carried to it umbilical blood do not close up, but they transmit exclusively that of the vena porta, which increases a little in size, because digestion, which begins in the gastric organs, calls to them more arterial blood, and consequently more is returned by the veins. This slight increase does not compensate for the absence of the umbilical blood; thus the liver diminishes proportionally in size in an evident manner.

As to the ductus venosus, it is obliterated by the effect of the contractility of texture. The blood coming in the vena porta, has not, as I have said, any tendency to pass through it, because this canal is not in its direction; it passes rather into the hepatic vessels, and the circulation of the liver is established then, as it will always continue to be.

This then is the difference that birth brings to the hepatic circulation; 1st, less blood and only one kind entering the liver; 2d, an interruption of all communication between the general and abdominal black blood; 3d, proportional diminution of the size of the liver. Hence there is an inverse phenomenon for this organ and for the lungs. The latter increases, the other diminishes in activity and size.

The great quantity of blood that enters the liver before birth, and the size of this organ, compared to the small quantity of bile that escapes from it, are an evident proof then that it is destined for other uses besides the secretion of this fluid. There cannot be a doubt upon this point; it is a proof moreover, that in the adult the disproportion of the organ to the fluid, though less sensible, supposes also in it another important function of which we are ignorant.

There ought to be a precise relation between the obliteration of the ductus venosus, of the foramen ovale and the ductus arteriosus, between the increased activity of the lungs and the diminished activity of the liver at birth, &c. We judge of this relation, without knowing it, because a veil is still spread over the circulation of the fœtus. I would only observe that the predominance of the liver before birth, does not suppose any in the system of black abdominal blood; it arises exclusively from the umbilical vein; thus the proportional volume of this organ is constantly diminishing afterwards, especially on the left side, where this vein is distributed, as Portal has observed. It is difficult to name the period, at which the equilibrium is generally established.