William Harvey

by Sir D'Arcy Power

Such a statement is now a mere truism, because every one who starts upon a subject of original research follows the method adopted by Harvey. He learns thoroughly what is known already; he frames a working hypothesis and puts it to the test of experiment. He then combines his à priori reasoning with a logical deduction from the facts he observes. A feeble mind is sometimes overmastered by its working hypothesis, and may be led to consider it proved when a better trained observer would dismiss it for a more promising theory. Harvey’s hypothesis—tested by experiment, by observation, and by reasoning—was no longer an hypothesis but a proved fact fertile beyond measure, for it rendered possible a coherent and experimental physiology and a new medicine and surgery.

The anatomical treatise gives in seventeen short chapters a perfectly clear and connected account of the action of the heart and of the movement of the blood round the body in a circle. A movement which had been foreshadowed by some of the earlier anatomists and had been clearly indicated by Harvey himself as early as 1616. But it is here laid down with a precision of detail, with a logical exactness, and with a wealth of illustration which is marvellous even to us who read of the circulation as an established and fundamental principle upon which the whole body of physic rests. Harvey’s proof fell short of complete demonstration, for he had no means of showing how the smallest arteries are connected with the smallest veins. He worked, indeed, with a simple lens, but its magnifying power was too feeble to show him the arterioles and the venules, whilst the idea of an injection does not seem to have occurred to him. It was not until after the invention of the compound microscope that Leeuwenhoek, in 1675, described the blood corpuscles and the circulation in the capillary blood vessels, though they had already been seen by Malpighi.

The first chapter of the Treatise is introductory. It is a review of the chief theories which had been held as to the uses of the heart and lungs. It had been maintained that the heart was the great centre for the production of heat. The blood was driven alternately to and from the heart, being sucked into it during the diastole and driven from it during the systole. The use of the arteries was to fan and cool the blood, as the lungs fanned and cooled the heart, for the pulse was due to an active dilatation and contraction of the arteries. During their dilatation the arteries sucked in air, and during their contraction they discharged murky vapours through pores in the flesh and skin. In the heart, as well as in the arteries, the dilatation was of greater importance than the contraction. The whole of this tissue of falsehood seems to have been founded upon an incorrect apprehension of the nature of heat. It was looked upon as a fundamental principle or entity, and until chemistry and physics reached the stage of experimental sciences it was impossible to give a correct explanation of the phenomena it presents. Even Harvey sometimes lost himself in mysticism when he had to deal with the subject of animal heat, though he was struggling hard to find a firm foothold when he said, “We are too much in the habit of worshipping names to the neglect of things. The word Blood has nothing of grandiloquence about it, for it signifies a substance which we have before our eyes and can touch; but before such titles as Spirit and Calidum Innatum [or inherent heat] we stand agape.”

Harvey begins his Treatise on the movement of the Heart and Blood with the clear statement that the heart must be examined whilst it is alive; but he says, “I found the task so truly arduous and so full of difficulties that I was almost tempted to think with Fracastorius that the movement of the heart was only to be comprehended by God. For I could neither rightly perceive at first when the systole[10] and when the diastole took place, nor when and where dilatation and contraction occurred, by reason of the rapidity of the movement, which in many animals is accomplished in the twinkling of an eye, coming and going like a flash of lightning.

“At length by using greater and daily diligence and investigation, making frequent inspection of many and various animals and collating numerous observations, I thought that I had attained to the truth ... and that I had discovered what I so much desired—both the movement and the use of the heart and arteries. From that time I have not hesitated to expose my views upon these subjects, not only in private to my friends, but also in public in my anatomical lectures, after the manner of the Academy of old.

“These views, as usual, pleased some more, others less: some chid and calumniated me and laid it to me as a crime that I had dared to depart from the precepts and opinion of all anatomists: others desired further explanations of the novelties, which they said were both worthy of consideration, and might perchance be found of signal use.”

The results of his experiments soon made it plain to Harvey that the heart’s movements could be studied more readily in the colder animals, such as toads, frogs, serpents, small fishes, crabs, shrimps, snails, and shell-fish, than in warm-blooded animals. The movements of the heart became more distinct even in warm-blooded animals, such as the dog and hog, if the organ was attentively noted when it began to flag. The movements then became slower, the pauses longer, so that it was then much more easy to perceive and unravel what the movements really were and how often they were performed.

Careful observation and handling the heart made it clear that the organ was muscular, and that its systole was in every way comparable with the contraction which occurs in the muscles of the forearm when the fingers are moved. “The contraction of the heart is therefore of greater importance than its relaxation. During its contraction the heart becomes erect, hard, and diminished in size, so that the ventricles become smaller and are so made more apt to expel their charge of blood. Indeed, if the ventricle be pierced the blood will be projected forcibly outwards at each pulsation when the heart is tense.”

After thus disproving the erroneous views of the heart’s action, Harvey next proceeds to discuss the movements in the arteries as they are seen in the dissection of living animals. He shows that the pulsation of the arteries depends directly upon the contraction of the left ventricle and is due to it, whilst the contraction of the right ventricle propels its charge of blood into the pulmonary artery which is distended simultaneously with the other arteries of the body. When an artery is divided or punctured the blood is forcibly expelled from the wound at the instant when the left ventricle contracts, and when the pulmonary artery is wounded the blood spurts forth with violence when the right ventricle contracts. So also in fish, if the vessel leading from the heart to the gills be divided the blood flows out forcibly when the heart becomes tense and contracted.

These facts enabled Harvey to disprove the current theory that the heart’s systole corresponded with the contraction of the arteries which then became filled with blood by a process of active dilatation, as bellows are filled with air. He illustrated this by a homely method which he had been accustomed to use in his lectures for years. He says that “the pulses of the arteries are due to the impulses of the blood from the left ventricle may be illustrated by blowing into a glove, when the whole of the fingers will be found to become distended at one and the same time and in their tension to bear some resemblance to the pulse.”