The book contains the matured account of the circulation of the blood, of which somewhat more than the germ had appeared in the notes of the Lumleian visceral lecture for 1616. It is a small quarto, containing seventy-two pages and a page and half of _errata_, for Harvey wrote a villainous hand, and communication between Germany and England was too slow, expensive, and uncertain to allow an author to correct his book sheet by sheet as it issued from the press. The Treatise opens with a dedication to Charles I. couched in fitting emblematical language, and signed "Your Most August Majesty's Most Devoted Servant, William Harvey." The dedication is followed by a preface addressed to "Dr. Argent [then President of the College of Physicians, and one of Harvey's intimate friends] as well as to the other learned physicians, his most esteemed colleagues." In this preface he excuses himself for the book, saying that he had already and repeatedly presented to them his new views of the movement and function of the heart in his anatomical lectures. And that he had now for nine years and more confirmed these views by multiplied demonstrations in their presence. He had illustrated them by arguments and he had freed them from objections of the most learned and skilful Anatomists. He then proceeds so modestly that it is difficult to realise how great an innovation he was really making when he says, "I profess both to learn and to teach anatomy, not from books but from dissections, not from the positions of philosophers but from the fabric of nature." 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.