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impede the circulation; if, in stenosis of the auriculo-ventricular orifices, they should contract, their contraction would impede the circulation still more; and if they should become hypertrophied, their contraction would again still further impede it. As the auricles are situated on top of the thick, firm, and unyielding bases of the ventricles, with the great outlets into the ventricles, and with the current of blood toward, them, aided by a certain suction-power of the ventricles, there is no necessity for any contraction of the auricle in a sound state; while, in extreme stenosis, the force of the auricle would, if it contracted, be mainly spent in driving back the blood upon the returning circulation through the dilated and open mouths of the veins.
There are cases occasionally met with of stenosis and regurgitation at both mitral and aortic orifices; cases in which the blood would be driven back into the left auricle by the contraction of the hypertrophied left ventricle with as much force as it is sent forward into the aorta. Now, in such a case, if a left auricle became hypertrophied, with its force mainly expended upon the blood in the pulmonary veins, it would be almost impossible for the circulation to continue. In aortic obstruction and regurgitation, we find enormously dilated and hypertrophied left ventricles, while the left auricles remain normal. Now, while the left ventricle is receiving regurgitant blood from the aorta by a force which is measured by its tension, for a frail auricle, filled from veins unprotected by valves, to contract with a force sufficient to empty its contents into this ventricle in a half-second of time, is a physical impossibility. In cases of incompetency of the mitral valves, with regurgitation and without obstruction, the systolic impulse is perceptible over an enlarged and dilated auricle, the impulse being caused by the ventricle driving the blood into the auricle; but the auricle, dilated and hypertrophied, with extreme stenosis of the mitral valve, never, by its contraction, causes a perceptible impulse. In a case of extreme mitral stenosis, instead of the obstruction to the circulation being overcome by the hypertrophy of the left auricle, it would only be increased; as nearly the whole force of the auricular contraction would be expended on the
blood in the pulmonary veins. If aortic regurgitation would cause the dilatation of the thick walls of the left ventricle, what would become of the gossamer-walls of the left auricle, and the still more delicate walls of the pulmonary veins, in a marked case of stenosis and mitral regurgitation, the auricles contracting?
There are cases of incompetency of the tricuspid valve, with regurgitation and without obstruction, in which the blood is made to pulsate distinctly in the jugular vein by the contraction of the right ventricle; but, however extreme be the insufficiency of this valve, and however hypertrophied the right auricle may be, no such impulse is observed following its contraction. In cases of extreme dilatation of the right auricle; with the so-called hypertrophy of its walls; with obstruction in front, at the tricuspid valve, and none behind; with the external jugular so superficial at the root of the neck that every wave in the blood can be distinctly seen and felt; with its proximity to the dilated right auricle, and its direct course; with the patient in the recumbent posture and the auricle full of blood, can a contraction of the auricle be conceived, so delicate that it can not be appreciated? Such a contraction must be no contraction at all.
Upon the relaxation of the ventricular walls, at the close of their contraction, the condition of the ventricles, of the auriculoventricular valves, and of the auricles and the veins running directly into them, is as follows: First. The veins and auricles are filled with blood; and this blood has the vis a tergo, here as elsewhere in the venous system, urging it on. Second. We have at the base of the auricles a free, open, and spacious outlet for this blood, this outlet leading directly into the ventricular cavity. Third. This cavity has been suddenly created by the elastic rebound of the ventricular walls, a rebound sufficient in force to create a suction-power which the manometer has measured in the hands of reliable observers. Here, then, we have two distinct powers, a vis a tergo and a vis a frontis; and for what? Simply to pour the blood out of one vessel into another; the two being situated one above the other, and separated only by a cover (the valves) which has been removed. Are not these
forces and conditions all-sufficient to effect the object? Would not the creation of another force complicate and burden, if it did not subvert, the purpose for which it was intended?
It is a rule in mechanics that unnecessary means for the accomplishment of a purpose not only burdens the machine, but renders it less efficient, if it do not defeat the very object it was intended to serve. Nature never provides unnecessary means. During the time that the auriculo-ventricular valves remain closed, which is while the ventricles are contracting, the mouths of the great veins, including their terminations, the auricles, are filling with blood. This time is estimated as about two fifths of a revolution of the heart. It is well known to be less than half a second. In this short time, the blood is driven, by the contraction of the ventricle, through the ventriculo-aortic opening, overcoming all resistance. A little more time is given to the ventricle to again fill itself. The blood is not collected from various sources; the supply is all ready, and the ventricle has simply to open itself, by the elasticity of its walls, as the walls of a rubber ball spring apart after having been pressed together, in order to again be filled. There is, on the part of the veins and their terminations, the auricles, no force required to empty themselves. There is no force to be overcome; but rather there are in front of them the open and spacious mouths of two thick-walled, empty, hollow organs, the ventricles, drawing by quite a considerable suction-power the blood from these sources. It would not do for the ventricles to rely upon the different veins separately, the right upon the two venæ cave and the left upon the four pulmonary veins, for the ready supply of blood to fill them, a supply that must be provided in half a second. And so we have the bulbous extremity, the auricle, a reservoir for these veins to empty into; one that has sufficient capacity to contain all the blood that flows into them during the time the ventricle is contracting and the auriculo-ventricular valve is closed, which, when drawn upon by the ventricles, can supply them quickly. The auricle has as many inlets as there are veins emptying into it, and but one outlet, that into the ventricle. The parts are so arranged as to give the venous system the full
benefit of the suction-power of the ventricle. The auriculoventricular valve being open, the auricle being full, and the mouths of the different veins that empty into it being open, all the suction-power of the ventricle is brought to bear upon the blood.
That the great veins emptying into the auricles are without valves to prevent the reflux of the blood, is strong evidence that the auricles were not intended to contract. In a case of extreme stenosis and insufficiency at the mitral or tricuspid orifice, if we begin with the consideration of the ventricular contraction, we shall find a strong current sent back against the course of the blood in the veins. This, together with the returning blood in the veins beyond, overfills the auricle and the veins at their junction with it; and now the auricle, if contracting upon the blood which distends it, would keep up counter-force to the natural current. Auricular contraction in these cases would furnish a constant counter-force to the natural course of the blood in the veins. It is here that any provision of a compensatory character, in the well-known way of increased development of the muscular structure (hypertrophy) of the auricle, would necessarily increase the obstruction to the returning circulation, exactly in proportion to the extent of the hypertrophy.
Fortunately, however, we find no such hypertrophy, and that for the simple reason that contraction is not a function of the auricle, the slight thickening found in the walls of the auricle in some of these cases being common to the walls of the auricle and veins alike, and only such as the increased tension, caused by their increased capacity and the action of the ventricle, demands. There is in the Museum in Washington a specimen (No. 1536) which shows, in a most remarkable manner, the effect of stenosis and insufficiency at the mitral orifice upon the auricles. Both auricles are remarkably dilated, and both have remarkably attenuated walls, those of the right auricle being no thicker than ordinary brown paper. The history of this case shows that it was one of long standing, the patient having died at the age of forty. The ventricle is hypertrophied. Here is a case in
which there should have been hypertrophy of the auricles, if these parts contract; but, instead, there is dilatation and attenuation-a condition of things which is never found in cases in which the ventricle is similarly situated as regards increased action. How can an auricle that has become extremely attenuated and dilated to the size of a man's fist fill a ventricle in half of a second through an unyielding orifice less than one third of an inch in diameter, when the opposite outlet is open and spacious?
In the Army Museum can also be seen a large and most excellently preserved collection of hearts showing dilatation of the auricles from various causes. These cases range from the most trifling increase in the capacity of the cavities to the most extreme; and, while the thickness of the walls varies considerably, they can not be said in a single instance to show any more thickening than the veins that empty into them; not a single specimen, either by the thickness of its walls or the character of its texture, showing true hypertrophy resulting from increased action of the part. Hypertrophy proper of the auricles is a myth. We find the same hypertrophy in the veins emptying into the auricles, in varicose veins of the lower extremity, etc. Again, long-continued obstruction of the aortic or pulmonary orifices, without regurgitation, causes hypertrophy of the ventricles only. Why, if the auricles contract, do we not have hypertrophy only of these in cases of like obstruction from disease of the mitral and tricuspid orifices? There are some cases of stenosis of the mitral and tricuspid orifices in which the aperture through which the blood must pass will not much more than admit an ordinary lead-pencil. If a distended and hypertrophied auricle contract upon its contents in these cases, in which direction will the blood be driven; into the ventricle, through this narrow, unyielding aperture, or back through the enlarged and open mouths of the veins upon the returning circulation? Imagine, now, the effects upon the circulation of the additional regurgitation of blood from ventricular contraction. In these cases, if the auricle contract, there must be a strong current sent back upon