The Great Events by Famous Historians [Volumes 1-14]

It must further be borne in mind that the determination of the true course taken by the whole mass of the blood is only the most conspicuous of the discoveries of Harvey; and that his analysis of the mechanism by which the circulation is brought about is far in advance of anything which had previously been published. For the first time it is shown that the walls of the heart are active only during its systole or contraction, and that the dilatation of the heart, in the diastole, is purely passive. Whence it follows that the impulse by which the blood is propelled is a vis à tergo, and that the blood is not drawn into the heart by any such inhalent or suctorial action as not only the predecessors, but many of the successors, of Harvey imagined it to possess.

Harvey is no less original in his view of the cause of the arterial pulse. In contravention of Galen and of all other anatomists up to his own time, he affirms that the stretching of the arteries which gives rise to the pulse is not due to the active dilatation of their walls, but to their passive distention by the blood which is forced into them at each beat of the heart; reversing Galen's dictum, he says that they dilate as bags and not as bellows. This point of fundamental, practical as well as theoretical, importance is most admirably demonstrated, not only by experiment, but by pathological illustrations.

One of the weightiest arguments in Harvey's demonstration of the circulation is based upon the comparison of the quantity of blood driven out of the heart, at each beat, with the total quantity of blood in the body. This, so far as I know, is the first time that quantitative considerations are taken into account in the discussion of a physiological problem. But one of the most striking differences between ancient and modern physiological science, and one of the chief reasons of the rapid progress of physiology in the last half-century, lies in the introduction of exact quantitative determinations into physiological experimentation and observation. The moderns use means of accurate measurement which their forefathers neither possessed nor could conceive, inasmuch as they are products of mechanical skill of the last hundred years, and of the advance of branches of science which hardly existed, even in germ, in the seventeenth century.

Having attained to a knowledge of the circulation of the blood, and of the conditions on which its motion depends, Harvey had a ready deductive solution for problems which had puzzled the older physiologists. Thus the true significance of the valves in the veins became at once apparent. Of no importance while the blood is flowing in its normal course toward the heart, they at once oppose any accidental reversal of its current which may arise from the pressure of adjacent muscles or the like. And in like manner the swelling of the veins on the farther side of the ligature, which so much troubled Cæsalpinus, became at once intelligible as the natural result of the damming up of the returning current.

In addition to the great positive results which are contained in the treatise which Harvey modestly calls an Exercise and which is, in truth, not so long as many a pamphlet about some wholly insignificant affair, its pages are characterized by such precision and simplicity of statement, such force of reasoning, and such a clear comprehension of the methods of inquiry and of the logic of physical science, that it holds a unique rank among physiological monographs. Under this aspect, I think I may fairly say that it has rarely been equalled and never surpassed.

Such being the state of knowledge among his contemporaries, and such the immense progress effected by Harvey, it is not wonderful that the publication of the Exercitatio produced a profound sensation. And the best indirect evidence of the originality of its author, and of the revolutionary character of his views, is to be found in the multiplicity and the virulence of the attacks to which they were at once subjected.

Riolan, of Paris, had the greatest reputation of any anatomist of those days, and he followed the course which is usually adopted by the men of temporary notoriety toward those of enduring fame. According to Riolan, Harvey's theory of the circulation was not true; and besides that, it was not new; and, furthermore, he invented a mongrel doctrine of his own, composed of the old views with as much of Harvey's as it was safe to borrow, and tried therewith to fish credit for himself out of the business. In fact, in wading through these forgotten controversies, I felt myself quite at home. Substitute the name of Darwin for that of Harvey, and the truth that history repeats itself will come home to the dullest apprehension. It was said of the doctrine of the circulation of the blood that nobody over forty could be got to adopt it; and I think I remember a passage in the Origin of Species to the effect that its author expects to convert only young and flexible minds.