The circulation of the blood was first taught by the unfortunate Servetus in 1553, who was burnt to death as a heretic; and, a century afterwards, demonstrated by our Harvey, who is justly considered as having discovered the wonderful mechanism of the motion of the vital fluid.

There is no doubt, however, that the ancients had formed, if not a correct, at least an ingenious, idea of it. Hippocrates tells us “that all the veins communicate with each other, and flow from one vessel into others; and that all the veins that are spread over the body carry a flux and movement originating in a single vessel.” He avows that he is ignorant of the principle whence it arises, or of its termination, it appearing to be a circle without beginning or end. He further states, that the heart is the source of the arteries, through which blood is carried over the body, communicating life and heat; and he adds, that they are so many rivulets that irrigate the system, and carry vitality into every part: the heart and veins are in constant motion; and he compares the circulation of blood to the course of rivers, that return to their source by extraordinary deviations. He therefore directs blood-letting to restore a free current of the blood and other spirits in apoplexies and other diseases of a similar nature, which he attributed to obstruction in the vessels intercepting the flow of their contents. He also observes, that when bile enters the blood, it deranges its consistence, and disturbs its ordinary course towards another point: and he compares the circulation to balls of thread, the threads of which return to each other in a circuitous manner, terminating at the point whence their motion arose.

Plato thought that the heart was the source of the veins, and of the blood, that was rapidly borne to every part of the body. Aristotle tells us that the heart is the principle and source of the veins and of the blood. He considered that there were two veins proceeding from this organ, one from the left side, the other from the right; the first he termed aorta: and he further maintained that the arteries communicated with the veins, with which they were intimately connected.

Julius Pollux taught, in his Gnomasticon, that the arteries are the channels through which the spirits circulate as the veins propel the blood; and he describes the heart as having two cavities, one communicating with the arteries, and the other with the veins. Apuleius tells his disciples that the heart propels the blood through the lungs, to be afterwards distributed over the system.

In the writings of Nemesius, bishop of Emissa, we read that the movement observed in the pulse originates in the heart, chiefly from the artery of the left ventricle of the viscus. This artery is dilated, and then contracted, by a constant and powerful harmonious action. When dilated the vessel draws towards it the most subtile portions of the neighbouring blood, and the vapour or exhalation of this fluid, that feeds the animal spirits; but when it contracts, it exhales, through various channels of the body, all the vapours that it contains.

Strange as it may appear, doubts were once entertained as to the actual situation of the heart, whether it was lodged in the right or the left side of the body. The question was finally settled by a professor of Heidelberg, who for the purpose killed a pig in the presence of the Margrave of Baden, Durlach, who then laboured under a supposed disease of that organ, which it was then clearly shown occupied the left side. The result of this experiment, however proved somewhat detrimental to his Highness’s physician, who was dismissed, although he maintained with all becoming courtesy and respect, that the heart of his princely master could not possibly be in the same position as that of a hog.

Michael Servetus, in his work, De Christianismi restitutione, also in the 7th book, De Trinitate DivinÂ, for which he was sentenced to the stake a very short time after its publication, gives us the following description of this important function: The blood, which is a vital spirit, is diffused all over the body by anastomoses, or inosculation of two vessels through their extremities. The air in the lungs contributes to the elaboration of the blood, which it draws for that purpose from the right ventricle of the heart through the pulmonary artery. This blood is prepared in the lungs by a movement of the air that agitates it, subtilizes it, and, finally, mingles it with that vital spirit which is afterwards retransmitted to the heart by the movement of the diastole, as a vital fluid proper to maintain life. This communication and preparation of the blood, he further states, is rendered evident by the union of the arteries and veins in this organ; and he concludes by affirming that the heart, having thus received the blood prepared by the lungs, transmits it through the artery of the left ventricle, or the aorta, to every part of the body.

Great care was of course taken to destroy this abominable heretical publication, which was burnt by the common hangman in Geneva, Frankfort, and several provinces of France. The work thence became so scarce, that it is said only three or four copies of it are in existence. One of them was in the library of the Landgrave of Hesse-Cassel.

John Leonicenus relates that the celebrated Paul Sarpi otherwise named Fra Paolo, had also discovered this circulation, and demonstrated the valves of the veins, which open to afford a free passage to the blood, and close to prevent its return. This discovery, it is pretended, was made known to Fabricius ab Aquapendente, professor of medicine in Padua in the sixteenth century, and successor of Fallopius, and who communicated the fact to Harvey, then a student in that university.

Some time before Harvey’s discovery, Cesalpinus had described with great precision the pulmonary circulation; and, on finding that veins swelled under a ligature, he attributed this enlargement to the warmth of the blood. This warmth, he says, proceeds from a spirit residing in the blood. The left ventricle is filled with blood of a spirituous nature; and one can trace the movement of the blood towards the superior parts, and its return (retrocessus) to the internal ones,—that is to say, a return by which it comes back from the extremities to the heart, when awake or sleeping, from every part of the body; for if you tie the vessels, or if they are obstructed, the current of the blood is stopped, and then their smaller ramifications tumefy towards their origin. The following are his words: “Sic non obscurus est ejusmodi motus in quÂcumque corporis parte, si vinculum adhibeatur, aut ali ratione occludantur venÆ: cÙm enim tollitur permeatio, intumescunt rivuli qu parte fluere solent.” From these expressions it is clear that Cesalpinus suspected the great circulation, and had a fair idea of its nature; yet there is no doubt but that it was to our Harvey that the first demonstration of this wondrous function was reserved.