valves was unsuspected, and the fact of even the pulmonary circulation was not generally admitted in its full meaning.
In his treatise Harvey proves (1) that it is the contraction, not the dilatation, of the heart which coincides with the pulse, and that the ventricles as true muscular sacs squeeze the blood which they contain into the aorta and pulmonary artery; (2) that the pulse is not produced by the arteries enlarging and so filling, but by the arteries being filled with blood and so enlarging; (3) that there are no pores in the septum of the heart, so that the whole blood in the right ventricle is sent to the lungs and round by the pulmonary veins to the left ventricle, and also that the whole blood in the left ventricle is again sent into the arteries, round by the smaller veins into the venæ cavæ, and by them to the right ventricle again thus making a complete "circulation"; (4) that the blood in the arteries and that in the veins is the same blood; (5) that the action of the right and left sides of the heart, auricles, ventricles, and valves, is the same, the mechanism in both being for reception and propulsion of liquid and not of air, since the blood on the right side, though mixed with air, is still blood; (6) that the blood sent through the arteries to the tissues is not all used, but that most of it runs through into the veins; (7) that there is no to and fro undulation in the veins, but a constant stream from the distant parts towards the heart; (8) that the dynamical starting-point of the blood is the heart and not the liver.
The method by which Harvey arrived at his complete and almost faultless solution of the most fundamental and difficult problem in physiology has been often discussed, and is well worthy of attention. He begins his treatise by pointing out the many inconsistencies and defects in the Galenical theory, quoting the writings of Galen himself, of Fabricius, Columbus, and others, with great respect, but with unflinching criticism. For, in his own noble language, wise men must learn anatomy, not from the decrees of philosophers, but from the fabric of nature herself, "nec ita ia verba jurare antiquitatis magistræ, ut veritatem amicam in apertis relinquant, et in conspectu omnium deserant." He had, as we know, not only furnished himself with all the knowledge that books and the instructions of the best anatomists of Italy could give, but, by a long series of dissections, had gained a far more complete knowledge of the comparative anatomy of the heart and vessels than any contemporary—we may almost say than any successor, until the times of Hunter and Meckel. Thus equipped, he tells us that he began his investigations into the movements of the heart and blood by looking at them—i.e., by seeing their action in living animals. After a modest preface, he heads his first chapter "Ex vivorum dissectione, qualis sit cordis motus." He minutely describes what he saw and handled in dogs, pigs, serpents, frogs, and fishes, and even in slugs, oysters, lobsters, and insects, in the transparent minima squilla, "quæ Anglice dicitur a shrimp" and lastly in the chick while still in the shell. In these investigations he used a perspicillum or simple lens. He particularly describes his observations and experiments on the ventricles, the auricles, the arteries, and the veins. He shows how the arrangement of the vessels in the fœtus supports his theory. He adduces facts observed in disease as well as in health to prove the rapidity of the circulation. He explains how the mechanism of the valves in the veins is adapted, not, as Fabricius believed, to moderate the flow of blood from the heart, but to favour its flow to the heart. He estimates the capacity of each ventricle, and reckons the rate at which the whole mass of blood passes through it. He elaborately and clearly demonstrates the effect of obstruction of the blood-stream in arteries or in veins, by the forceps in the case of a snake, by a ligature on the arm of a man, and illustrates his argument by figures. He then sums up his conclusion thus:—"Circular quodam motu, in circuitu, agitari in animalibus sanguinem, et esse in perpetuo motu; et hanc esseactionem sive functionem cordis quam pulsu peragit; et omnino motus et pulsus cordis causam unam esse." Lastly, in the 15th, 16th, and 17th chapters, he adds certain confirmatory evidence, as the effect of position on the circulation, the absorption of animal poisons and of medicines applied externally, the muscular structure of the heart and the necessary working of its valves. The whole treatise, which occupies only 67 pages of large print in the quarto edition of 1766, is a model of accurate observation, patient accumulation of facts, ingenious experimentation, bold yet cautious hypothesis, and logical deduction.
In one point only was the demonstration of the circulation incomplete. Harvey could not discover the capillary channels by which the blood passes from the arteries to the veins. This gap in the circulation was supplied several years later by the great anatomist Malpighi, who in 1661 saw in the lungs of a frog, by the newly invented microscope, how the blood passes from the one set of vessels to the other. Harvey saw all that could be seen by the unaided eye in his observations on living animals; Malpighi, four years after Harvey's death, by another observation on a living animal, completed the splendid chain of evidence. If this detracts from Harvey's merit it leaves Servetus no merit at all. But in fact the existence of the channels first seen by Malpighi was as clearly pointed to by Harvey's reasoning as the existence of Neptune by the calculations of Le Verrier and of Adams.
Harvey himself and all his contemporaries were well aware of the novelty and importance of his theory. He says in the admirable letter to Dr Argent, president of the College of Physicians, which follows the dedication of his treatise to Charles I., that he should not have ventured to publish "a book which alone asserts that the blood pursues its course and flows back again by a new path, contrary to the received doctrine taught so many ages by innumerable learned and illustrious men," if he had not set forth his theory for more than nine years in his college lectures, gradually brought it to perfection, and convinced his colleagues by actual demonstrations of the truth of what he advanced. He anticipates opposition, and even obloquy or loss, from the novelty of his views. These anticipations however, the event proved to
but through the lungs, "quod nemo hactenus aut animadvertit aut scriptum reliquit." The fact that Harvey quotes Columbus and not Servetus is explained by the almost entire destruction of the writings of the latter, which are now among the rarest curiosities. The great anatomist Fabricius, Harvey's teacher at Padua, described the valves of the veins more perfectly than had Sylvius. Ruini, in his treatise on the Anatomy and Diseases of the Horse (1590), taught that the left ventricle sends blood and vital spirits to all parts of the body except the lungs—the ordinary Galenical doctrine. Yet on the strength of this phrase Professor Ercolani has actually put up a tablet in the veterinary school at Bologna to Ruini as the discoverer of the circulation of the blood! The claims of Cæsalpinus, a more plausible claimant to Harvey's laurels, are scarcely better founded. In his Quæstiones Peripateticæ (1571) he followed Servetus and Columbus in describing what we now know as the pulmonary "circulation" under that name, and this is the only foundation for the assertion (first made in Bayle's dictionary) that Cæsalpinus knew "the circulation of the blood." He is even behind Servetus, for he only allows part of the blood of the right ventricle to go round by this "circuit"; some, he conceives, passes through the hypothetical pores in the septum, and the rest by the superior cava to the head and arms, by the inferior to the rest of the body—"Hanc esse venarum utilitatem ut omnes partes corporis sanguinem pro nutrimento deferant. Ex dextro ventro cordis vena cava sanguinem crassiorem, in quo calor intensus est magis, ex altero autem ventro, sanguinem temperatissimum ac sincerissimum habente, egreditur aorta." Cæsalpinus seems to have had no original views on the subject; all that he writes is copied from Galen or from Servetus except some erroneous observations of his own. His greatest merit was as a botanist; and no claim to the "discovery of the circulation" was made by him or by his contemporaries. When it was made, Haller decided conclusively against it. The fact that an inscription was lately placed on the bust of Cæsalpinus at Rome, which states that he preceded others in recognizing and demonstrating "the general circulation of the blood," is only a proof of the blindness of misplaced national vanity.
