The Great Events by Famous Historians, Volume 11

by Unknown

Galen, moreover, correctly asserted—though the means of investigation at his disposition did not allow him to prove the fact—that the ramifications of the vena arteriosa in the substance of the lungs communicate with those of the arteria venosa, by direct, though invisible, passages, which he terms anastomoses; and that, by means of these communications, a certain portion of the blood of the right ventricle of the heart passes through the lungs into the left ventricle. In fact, Galen is quite clear as to the existence of a current of blood through the lungs, though not of such a current as we now know traverses them. For, while he believed that a part of the blood of the right ventricle passes through the lungs, and even, as I shall show, described at length the mechanical arrangements by which he supposes this passage to be effected, he considered that the greater part of the blood in the right ventricle passes directly, through certain pores in the septum, into the left ventricle. And this was where Galen got upon his wrong track, without which divergence a man of his scientific insight must infallibly have discovered the true character of the pulmonary current, and not improbably have been led to anticipate Harvey.

The best evidence of the state of knowledge respecting the motions of the heart and blood in Harvey's time is afforded by those works of his contemporaries which immediately preceded the publication of the Exercitatio Anatomica, in 1628. And none can be more fitly cited for this purpose than the de Humani Corporis Fabrica, Book X, of Adrian van den Spieghel, who, like Harvey, was a pupil of Fabricius of Aquapendente, and was of such distinguished ability and learning that he succeeded his master in the chair of anatomy of Padua.

Van den Spieghel, or Spigelius, as he called himself in accordance with the fashion of those days, died comparatively young, in 1625, and his work was edited by his friend Daniel Bucretius, whose preface is dated 1627. The accounts of the heart and vessels, and of the motion of the blood, which it contains, are full and clear; but, beyond matters of detail, they go beyond Galen in only two points; and with respect to one of these, Spigelius was in error.

The first point is the "pulmonary circulation," which is taught as Realdus Columbus taught it nearly eighty years before. The second point is, so far as I know, peculiar to Spigelius himself. He thinks that the pulsation of the arteries has an effect in promoting the motion of the blood contained in the veins which accompany them. Of the true course of the blood as a whole, Spigelius has no more suspicion than had any other physiologist of that age, except William Harvey; no rumor of whose lectures at the College of Physicians, commenced six years before Spieghel's death, was likely in those days of slow communication and in the absence of periodical publications to have reached Italy.

Now, let anyone familiar with the pages of Spigelius take up Harvey's treatise and mark the contrast.

The main object of the Exercitatio is to put forth and demonstrate by direct experimental and other accessory evidence a proposition which is far from being hinted at either by Spigelius or by any of his contemporaries or predecessors, and which is in diametrical contradiction to the views respecting the course of the blood in the veins which are expounded in their works.

From Galen to Spigelius, they one and all believed that the blood in the vena cava and its branches flows from the main trunk toward the smaller ramifications. There is a similar consensus in the doctrine that the greater part, if not the whole, of the blood thus distributed by the veins is derived from the liver; in which organ it is generated out of the materials brought from the alimentary canal by means of the vena portæ. And all Harvey's predecessors further agree in the belief that only a small fraction of the total mass of the venous blood is conveyed by the vena arteriosa to the lungs and passes by the arteria venosa to the left ventricle, thence to be distributed over the body by the arteries. Whether some portion of the refined and "pneumatic" arterial blood traversed the anastomotic channels, the existence of which was assumed, and so reached the systemic veins, or whether, on the contrary, some portion of the venous blood made its entrance by the same passages into the arteries, depended upon circumstances. Sometimes the current might set one way, sometimes the other.

In direct opposition to these universally received views Harvey asserts that the natural course of the blood in the veins is from the peripheral ramifications toward the main trunk; that the mass of the blood to be found in the veins at any moment was a short time before contained in the arteries, and has simply flowed out of the latter into the veins; and, finally, that the stream of blood which runs from the arteries into the veins is constant, continuous, and rapid.

According to the view of Harvey's predecessors, the veins may be compared to larger and smaller canals, fed by a spring which trickles into the chief canals, whence the water flows to the rest. The heart and lungs represent an engine set up in the principal canal to aerate some of the water and scatter it all over the garden. Whether any of this identical water came back to the engine or not would be a matter of chance, and it would certainly have no sensible effect on the motion of the water in the canals. In Harvey's conception of the matter, on the other hand, the garden is watered by channels so arranged as to form a circle, two points of which are occupied by propulsive engines. The water is kept moving in a continual round within its channels, as much entering the engines on one side as leaves them on the other; and the motion of the water is entirely due to the engines.

It is in conceiving the motion of the blood, as a whole, to be circular, and in ascribing that circular motion simply and solely to the contractions of the walls of the heart, that Harvey is so completely original. Before him, no one, that I can discover, had ever so much as dreamed that a given portion of blood, contained, for example, in the right ventricle of the heart, may, by the mere mechanical operation of the working of that organ, be made to return to the very place from which it started, after a long journey through the lungs and through the body generally. And it should be remembered that it is to this complete circuit of the blood alone that the term "circulation" can, in strictness, be applied. It is of the essence of a circular motion that that which moves returns to the place from whence it started. Hence the discovery of the course of the blood from the right ventricle, through the lungs, to the left ventricle was in no wise an anticipation of the discovery of the circulation of the blood. For the blood which traverses this part of its course no more describes a circle than the dweller in a street who goes out of his own house and enters his next-door neighbor's does so. Although there may be nothing but a party wall between him and the room he has just left, it constitutes an efficient défense de circuler. Thus, whatever they may have known of the so-called pulmonary circulation, to say that Servetus or Columbus or Cæsalpinus deserves any share of the credit which attaches to Harvey appears to me to be to mistake the question at issue.