The discovery made by Harvey was this: That the blood passed from the heart into the arteries, thence to the veins, by which it was brought back to the heart again; that the blood moved more or less in a circle, coming back eventually to the point from which it started. In a phrase, there was a Circulation of the Blood. Moreover, this circulation was of a double nature--one circle being from the right side of the heart to the left through the lungs, hence called the Pulmonary or Lesser Circulation; the other from the left side of the heart to the right, through the rest of the body, known as the Systemic or Greater Circulation. Further, that it was the peculiar office of the heart to maintain this circulation by its continuous rhythmic beating as long as life lasts. This appears very plain and simple to us now--so easy that he who runs may read: as important as simple, for without this knowledge it is no exaggeration to say that a real understanding of any important function of the human body was impossible. And hence it has been contended with much force that not only the science of physiology, but the scientific practice of medicine date from this discovery. “To medical practice,” says Sir John Simon, “it stands much in the same relation as the discovery of the mariner’s compass to navigation; without it, the medical practitioner would be all adrift, and his efforts to benefit mankind would be made in ignorance and at random.... The discovery is incomparably the most important ever made in physiological science, bearing and destined to bear fruit for the benefit of all succeeding ages.”[2] [2] Harvey Tercentenary Memorial Meeting, Folkestone, September 6, 1871. When Harvey first approached the subject, there were all kinds of crude and fantastic ideas regarding the functions and uses of the heart, bloodvessels, and blood--that the heart was the workshop in which were elaborated the spirits, a due supply of which was necessary for many parts of the body; that from the heart the arteries carried spirits, the veins nutriment to the different parts of the body; that the arteries contained blood and air mixed together, or only air; that fuliginous vapours, whatever they may be, passed from the heart along the bloodvessels; that the septum of the heart, by which its two sides are completely separated, was riddled with minute holes, like a fine sieve, through which the blood percolated from the right to the left side; again, that the heart was the organ in which the heat of the body was produced. Another favourite theory was that the blood moved from the heart along certain bloodvessels and back again by exactly the same channels, after the manner of the rise and fall of the tides, to which in fact the movement was likened. More curious still, even the best informed appeared to believe that the arteries terminated in nerves.