Blood Circulation Discovered

This series has four easy 5 minute installments.

Introduction
Contemporary with Galileo and ranking but little below him in influence upon the modern world, was William Harvey. Harvey’s discovery of the circulation of the blood, combined with the truly scientific methods by which he reached and afterward proved, his great result, has placed his name high on the roll of science. Not only does his work stand at the foundation of modern anatomy and medicine but it has given him place in the ranks of great philosophers as well. Huxley, himself so long and justly renowned in modern science, rises to enthusiasm in the following account of his mighty predecessor.

Harvey was born at Folkestone, England, in 1578 and lived till 1657. He was educated as a physician, studying at Padua in Italy and was early appointed a lecturer in the London College of Physicians. In his lectures, somewhere about the year 1616 or a little later, he began to explain his new doctrine to his students; but it was not until the publication of his book Exercitatio Anatomica de Motu Cordis et Sanguinis, in 1628, that the theory spread beyond his immediate circle.

Huxley’s account will perhaps give a clearer idea of Harvey’s relation to his predecessors and contemporaries and of the value of his services to mankind, than would a far longer biography of the great physician, physiologist and anatomist.

This selection is by Thomas H. Huxley.

Time: 1616
Place: England

Many opinions have been held respecting the exact nature and value of Harvey’s contributions to the elucidation of the fundamental problem of the physiology of the higher animals; from those which deny him any merit at all — indeed, roundly charge him with the demerit of plagiarism — to those which enthrone him in a position of supreme honor among great discoverers in science. Nor has there been less controversy as to the method by which Harvey obtained the results which have made his name famous. I think it is desirable that no obscurity should hang around these questions; and I add my mite to the store of disquisitions on Harvey, in the hope that it may help to throw light upon several points about which darkness has accumulated, partly by accident and partly by design.

About the year B.C. 300 a great discovery, that of the valves of the heart, was made by Erasistratus. This anatomist found, around the opening by which the vena cava communicates with the right ventricle, three triangular membranous folds, disposed in such a manner as to allow any fluid contained in the vein to pass into the ventricle but not back again. The opening of the vena arteriosa into the right ventricle is quite distinct from that of the vena cava; and Erasistratus observed that it is provided with three pouch-like, half-moon-shaped valves; the arrangement of which is such that a fluid can pass out of the ventricle into the vena arteriosa but not back again. Three similar valves were found at the opening of the aorta into the left ventricle. The arteria venosa had a distinct opening into the same ventricle and this was provided with triangular membranous valves, like those on the right side but only two in number. Thus the ventricles had four openings, two for each; and there were altogether eleven valves, disposed in such a manner as to permit fluids to enter the ventricles from the vena cava and the arteria venosa respectively and to pass out of the ventricles by the vena arteriosa and the aorta respectively but not to go the other way.

It followed from this capital discovery that, if the contents of the heart are fluid and if they move at all, they can only move in one way; namely, from the vena cava, through the ventricle and toward the lungs, by the vena arteriosa, on the right side; and, from the lungs, by way of the arteria venosa, through the ventricle and out by the aorta for distribution in the body, on the left side.

Erasistratus thus, in a manner, laid the foundations of the theory of the motion of the blood. But it was not given to him to get any further. What the contents of the heart were and whether they moved or not, was a point which could be determined only by experiment. And, for want of sufficiently careful experimentation, Erasistratus strayed into a hopelessly misleading path. Observing that the arteries are usually empty of blood after death, he adopted the unlucky hypothesis that this is their normal condition and that during life they are filled with air. And it will be observed that it is not improbable that Erasistratus’ discovery of the valves of the heart and of their mechanical action strengthened him in this view. For, as the arteria venosa branches out in the lungs, what more likely than that its ultimate ramifications absorb the air which is inspired; and that this air, passing into the left ventricle, is then pumped all over the body through the aorta, in order to supply the vivifying principle which evidently resides in the air; or, it may be, of cooling the too great heat of the blood? How easy to explain the elastic bounding feel of a pulsating artery by the hypothesis that it is full of air! Had Erasistratus only been acquainted with the structure of insects, the analogy of their tracheal system would have been a tower of strength to him. There was no prima-facie absurdity in his hypothesis — and experiment was the sole means of demonstrating its truth or falsity.

More than four hundred years elapsed before the theory of the motion of the blood returned once more to the strait road which leads truthward; and it was brought back by the only possible method, that of experiment. A man of extraordinary genius, Claudius Galenus, of Pergamus, was trained to anatomical and physiological investigation in the great schools of Alexandria and spent a long life in incessant research, teaching and medical practice. More than one hundred fifty treatises from his pen, on philosophical, literary, scientific and practical topics, are extant; and there is reason to believe that they constitute not more than a third of his works. No former anatomist had reached his excellence, while he may be regarded as the founder of experimental physiology. And it is precisely because he was a master of the experimental method that he was able to learn more about the motions of the heart and of the blood than any of his predecessors and to leave to posterity a legacy of knowledge which was not substantially increased for more than thirteen hundred years.

The conceptions of the structures of the heart and vessels, of their actions and of the motion of the blood in them, which Galen entertained, are not stated in a complete shape in any one of his numerous works. But a careful collation of the various passages in which these conceptions are expressed leaves no doubt upon my mind that Galen’s views respecting the structure of the organs concerned were, for the most part, as accurate as the means of anatomical analysis at his command permitted; and that he had exact and consistent, though by no means equally just, notions of the actions of these organs and of the movements of the blood.

Continued.

We want to take this site to the next level but we need money to do that. Please contribute directly by signing up at https://www.patreon.com/history

Some History Moments selections posted before 2012 need to be updated to meet HM’s quality standards. These relate to: (1) links to outside sources for modern, additional information; (2) graphics; (3) navigation links; and (4) other presentation issues. The reader is assured that the author’s materiel is faithfully reproduced in all History Moments posts.