Book Description

Excerpt from An Experimental and Analytical Essay, on the Powers by Which the Blood Is Circulated in the Veins The powers which circulate the blood, have been subjects of ih quiry ever since the great discovery of the circulation, and numerous are the Opinions that have been offered to account for the motion of this fluid; and yet it may be fairly asked, what do we really know, on which there rests no doubt in addition to these facts, that the blood is circulated, and that it acquires motion by the contraction of the heart. It is true we do know a little more, but this little has been, I think, greatly overrated, both in respect to its importance, and the degree of certainty which is attached to it. Notwithstanding all that has been said on the subject of the dias tole of the cavities of the heart, it is not yet generally understood, whether the fibres of the heart are active or passive while the diastole is being efi'ected, -i. E. Whether the fibres constituting the muscular parietes of the auricles and ventricles of the heart, are relaxed in each cavity during the time in which they receive blood, or whether they are actively concerned in dilating the cavity into which the blood enters. The Opinion of harvey is that which almost generally prevails in the schools. He contended that a state of inertia or re laxation succeeded to the systole of the heart, and that the heart itself is the sole mover of the blood. Thus supposing the auricles to be full of blood, and the ventricles empty; the former, according to his view, contract, force the blood into the latter cavities, separate their relaxed walls from each other, and distend them. The ventri cles now filled with blood, contract; the tricuspid and mitral valves are closed by the pressure made on the blood; the semilunar valves are opened by the same cause; the blood is forced into the arteries of the greater and lesser circulation, it moves onwards through the artel ries into the veins, back again through the latter vessels to the auri cles of the heart with undiminished velocity, and these cavities it enters, dilates, &c. The blood from the right ventricle goes through the arteries of the lungs, and from these into the pulmonary veins, thence into the left auricle. The left auricle forces it into the left ventricle, which contracts, forces it into the aorta, thence into all parts of the system, from which it is continued in motion by the force impressed upon it, into the veins, and by these to the right side of the heart. About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.