William Harvey, M.D., the famous discoverer of the circulation of the blood, and the greatest physiologist the world has ever seen, was born at Folkestone, 1578. He entered Caius College, Cambridge, 1593. Having taken his degree, he travelled through France and Germany, and then visited Padua, the most celebrated school of medicine of that time. Fabricius ab Aquâpendente was then professor of anatomy, Minadous professor of medicine, and Casserius professor of surgery. In 1615 Harvey was appointed Lumleian lecturer, and he commenced his course of lectures in the following year—the year of Shakespeare’s death.
In this course he is supposed to have expounded his views on the circulation of the blood, which rendered his name immortal. His celebrated work, Exercitatio Anatomica de Motu Cordis et Sanguinis, was published in 1628; but he says in that work that for more than nine years he had confirmed and illustrated his opinion in his lectures, by arguments which were founded on ocular demonstration. He was appointed physician extraordinary to James I. in 1618. He was in attendance on King Charles I. at the battle of Edgehill. The king had been an enlightened patron of Harvey’s researches, and had placed the royal deer parks at Hampton Court and Windsor at his disposal. In 1651 Harvey’s Exercitationes de Generatione was published.
Aristotle knew but little of the vessels of the body, yet he traced the origin of all the veins to the heart, and he seems to have been aware of the distinction between veins and arteries. “Every artery,” he says, “is accompanied by a vein; the former are filled only with breath or air.”[890]
Aristotle thought that the windpipe conveys air into the heart. Although Galen understood the muscles very well, he knew little of the vessels. The liver he held to be the origin of the veins, and the heart of the arteries. He knew, however, of their junctions or anastomoses.[891]
Mondino, the anatomist of Bologna, who dissected and taught in 1315, had some idea of the circulation of the blood, for he says that the heart transmits blood to the lungs.[892] The great Italian anatomists diligent students as they were of the human frame, all missed the great discovery. Servetus, who was burnt by Calvin as a heretic in Geneva in 1553, is the first person who distinctly describes the small circulation, or that which carries the blood from the heart to the lungs and back again to the heart. He says:[893] “The communication between the right and left ventricles of the heart is made, not as is commonly believed, through the partition of the heart, but by a remarkable artifice the blood is carried from the right ventricle by a long circuit through the lungs; is elaborated by the lungs, made yellow, and transferred from the vena arteriosa into the arteria venosa.” Still, his theories are full of fancies about a “vital spirit, which has its origin in the left ventricle,” and are accordingly unscientific to that extent. Servetus was, however, certainly the true predecessor of Harvey in physiology; this is universally admitted.[894]
Realdus Columbus[895] is thought by some writers to have had a still greater share than Servetus in the discovery of the circulation. He denies the muscularity of the heart, yet correctly teaches that the blood passes from the right to the left ventricle, not through the partition in the heart but through the lungs. Harvey quotes Columbus, but does not refer to Servetus. It must be remembered that when the unfortunate Servetus was burnt at the stake, his work was destroyed with him, and only two copies are known to have escaped the flames.[896]
The discovery of the valves of the veins by Sylvius and Fabricius[897] undoubtedly was the chief factor in the preparation for Harvey’s discovery of the circulation. It was he who first appreciated their significance, and grasped the full meaning of the pulmonary circulation. Cæsalpinus, in his Quæstiones Peripateticæ (1571), is another claimant for the honours due to Harvey; he had certain confused ideas of the general circulation, and he made some experiments which enabled him to understand the pulmonary circulation, but he certainly did not know the circulation of the blood as a whole; he knew no more of it, in fact, than he gathered from Galen and Servetus.[898]
Even Harvey, splendid as was the work he did, could not entirely demonstrate the complete circulation of the blood. He was not able to discover the capillary vessels by which the blood passes from the arteries to the veins. This, the only missing point, was reserved for Malpighi to discover. In 1661 this celebrated anatomist saw in the lungs of a frog, by the aid of the newly invented microscope, the blood passing from one set of vessels to the other.
Harvey began his investigations by dissecting a great number of living animals. He examined in this way dogs, pigs, serpents, frogs, and fishes. He did not disdain to learn even from slugs, oysters, lobsters, and insects, and the chick itself while still in the shell. He observed and experimented upon the ventricles, the auricles, the arteries, and the veins. He learned precisely the object of the valves of the veins—to favour the flow of the blood towards the heart; and it was to this latter observation, and not the vivisection, that he attributed his splendid discovery.
“I remember,” says Boyle, “that when I asked our famous Harvey what were the things that induced him to think of a circulation of the blood, he answered me, that when he took notice that the valves in the veins of so many parts of the body were so placed, that they gave a free passage to the blood towards the heart, but opposed the passage of the venal blood the contrary way, he was incited to imagine that so provident a cause as Nature had not placed so many valves without design; and no design seemed more probable than that the blood should be sent through the arteries, and return through the veins, whose valves did not oppose its cause that way.” What clear views of the motions and pressure of a fluid circulating in ramifying tubes must have been held by Harvey to enable him to deduce his discovery from a contemplation of the simple valves! It was observation, experience, which led him to this. “In every science,” he says,[899] “be it what it will, a diligent observation is requisite, and sense itself must be frequently consulted. We must not rely upon other men’s experience, but our own, without which no man is a proper disciple of any part of natural knowledge.”