460. CHAPTER VII. THE MOTION OF THE ADULT HEART.
BOERHAAVE. "The heart and its auricles are real muscles, and act with a muscular force; they act, that is to say, when all its fibres, simultaneously shortened, diminish the length of the heart, increase its breadth, accurately contract the cavities of both ventricles, dilate the tendinous lips at the mouths of the arteries, shut down the lid like valves of the venous orifices, and express the contained liquids with great force, through the dilated mouths, into the arteries. This is the systole, or violent contraction of the heart, in whose structure there seems to be a wonderful and occult propensity to perform reciprocal acts of systole and diastole, and this, not only during life, but even after death; nay, after the heart has been separated from the body, and even when it is cut in pieces. And that the blood is then forced out, and propelled by this muscular contraction, is proved by its jetting forth when the pulmonary artery, or the aorta, is opened near the heart in a living animal; by its expulsion from the heart, when the cone of the latter is raised upwards, and a slice or section taken from its apex; by the pressure upon the finger when inserted into the wound thus made; by the swelling, tension, hardness, and paleness of the fibres; by their contraction succeeding and not preceding the act of impletion; and by the depletion being concomitant upon the shortening of the heart. If the eighth pair of nerves be tied, or divided, in the neck, the motion of the heart languishes, palpitation ensues, with great distress to the animal, and in a short time the motion wholly ceases; which shows that the origin and continuation of the systole of the heart is attributable to these nerves...." (Observe, this is according to Lower; but as to whether it be true or not, see Morgagni, Advers. Anat. v., Anim. 18.) "When the blood is thus almost wholly expelled from the cavities and vessels of the heart by its systole, its [muscular] fibres grow flaccid, from the compression of their nerves by the dilatation of the large arteries; and the coronary arteries being empty, the fibres are narrowed and elongated, and the distance between the base and the apex of the heart is increased; the pressure of the walls on the cavities is taken off; the valves of the venous inlets [from the auricles to the ventricles] are drawn towards the apex of the heart by the fleshy columns to which they are attached; the auricles and venous sinuses contract, and fill the cavities of the ventricles. This is the diastole, or the natural state of the heart. For that at the time of diastole the ventricles of the heart are filled with blood, may be demonstrated by opening one of the large arteries near the heart; by turning the heart of a living animal upward, and cutting it transversely, when it will be seen to receive the blood during diastole, and not to discharge it; by the inspection of animals opened a little before death; by the absence in diastole of pressure upon the finger when inserted into the ventricles through an incision. It is evident, therefore, that the blood does not pass out of the heart from any rarefaction, but from the muscular force of the organ. (Inst. Med., n. 187, 191.)
"The blood conveyed to the venous sinus may be driven by its hollow muscle into the right auricle, when relaxed, for there is then nothing to oppose it, but its progress is assisted by the motion of the subsequent venous blood pressed in the same direction. But since the right auricle, like the left, is a large, hollow muscle, furnished with innumerable arteries and veins, and composed of two rows of strong fibres, running in contrary directions to opposite tendons, and leaning by one tendon on the venous mouth of the right ventricle, while it is attached by the other and harder tendon, which is nearly circular, to the vena cava, it is evident that by the contractile force of this last, the blood may be expelled with a powerful impetus into the right ventricle, when relaxed. For the heart being then empty and elongated, and the three tricuspid valves drawn back towards its sides and apex, by the tapering and oblong fleshy papillae arising from the sides of the right ventricle, and which are themselves also drawn back; and hence the passage being sufficiently open, there is nothing at all to obstruct the entrance of the blood. The structure of the part, the phenomena presented by vivisection, inflation, and injection, all prove the same thing. (Ibid., n. 147, 150.)
"The venous blood, therefore (that is, of the whole body), is carried with a perpetual, swift, and violent motion, from the venous sinus, through the right auricle, and through the right ventricle, into the pulmonary artery alone. The left venous sinus receives all the pulmonary blood from the four great concurrent pulmonary veins, and by its muscular action is enabled to propel it into the left auricle, when relaxed (which auricle is much smaller than the right, although similarly constructed and situated), for there is nothing to prevent the blood from entering. So for a like reason, the blood can be easily propelled into the left ventricle when relaxed, through the two mitral valves, which have a similar mechanism to the tricuspids mentioned before; but it cannot return the same way. Moreover, by the action of the three semilunar valves placed at the beginning of the aorta, the blood is again determined straight into the aorta, for the same reasons as alleged above, and this, especially if the aorta be quiescent; and the passage is accurately closed against the return of the blood. We are here speaking of the adult subject, and of those of our species who live in the usual manner. All the pulmonary blood, then, is conveyed with a continual, rapid, and violent motion, from the lungs into the left vencas sinus, the left auricle, and the left ventricle, and so into the sorts. This motion is clearly accompanied with the following circumstances in the living subject.
1. Both the venous sinuses are filled, turgid, and red, at one and the same time; and so are both the auricles.
2. Both the auricles become flaccid at the same instant, end so also do both the venous sinuses.
3. At the very moment that the auricles become flaccid, they are filled with blood, by the impulse of that in the veins, and by the contractile action of the adjoining muscular venous sinus.
4. At the same instant, both ventricles contract, are emptied of blood, become pale, and the two great arteries are filled and dilated.
5. At the moment after this constriction, each empty ventricle is flaccid, elongated, and reddened, and its cavity enlarged.
6. Scarcely has this happened, when both auricles, and both muscular venous sinuses, contract with a muscular motion, express the blood they contain, and propel it into the ventricles; and now the auricles become pale.
7. In the mean time the venous sinuses and auricles are again filled, as before; in fine, the same series of acts occurs again, and so continues till the fainting animal is just dead.
8. When death approaches, the auricles and venous sinuses palpitate several times to one contraction of the ventricles. At length the left ventricle first ceases to move, and then its auricle; afterwards the right ventricle is still, and last of all the right auricle. The animal is now dead, after which we and the left ventricle empty, but the right ventricle always full of blood. Thus it appears that all the blood brought back from every point of the body, internal and external, and from every point of the heart, and from the auricles, is driven collectively into the right ventricle, thence is transmitted through the lungs into the left ventricle, and thence is sent all over the body, from whence it returns again to the heart. And this is the continual circulation of the blood, the glory of which discovery, with the proofs and explanation of it at large, will confer immortality on name of Harvey, whose doctrine has been confirmed by injection and transfusion, and has received ocular demonstration from the microscope. (Ibid., n. 155, 160.)
