This is the outline of the crude Galenic doctrine, and Vesalius, brilliant anatomist that he was content to accept it, although there are evidences that he was very skeptical re garding much of Galen's physiological teaching. It was particularly from the anatomical side that he was most skeptical; namely, because of the lack of tangible holes between the two sides of the heart, which were so important to the Galenists. His skepticism was taken up by his pupils and was also felt by others, one of them, Michael Servetus, who published a re markable book, the (Restitutio Christianismi,) in which a much of the cir culation of the blood was taught. This was as early as 1553. He rejected entirely the ancient doctrines and had grasped the true doctrine of the pulmonary circulation, the passage of the blood from the right side through the lungs to the left side. Servetus, however, was a theologian more than a physician and his early death probably prevented his further studies. Realdus Columbus, of Cremona, must be re garded as another link in the chain that led up to the final solution. He is thought to have been a tricky man, however, and one who would not hesitate to poach on another's pre serves, and there are indications of his copy ing much from Vesalius' works and claiming them as his own. He was vain and ignorant, but in his book, Re Anatomica' (1559), he described correctly the plumonary circula tion, but he was unable to draw from it the lessons that it implied. This, by many his torians, is taken as evidence that he was only a copier, and that probably the work of Ser vetus had been seen by him and he had claimed the discovery as his own. Cresalpinus, a noted botanist, was the first to appreciate the fact that on the contraction of the ventricles (sys tole) the blood was thrown into the aorta and into the pulmonary artery, and at its diastole it received the blood from the vena cava and the pulmonary vein. He also seemed to have grasped the fact of the flow of the blood from the arteries to the veins and of the flow along the veins to the heart. This was in 1571 and 1593. Thus Cmsalpinus had a true suggestion of the idea both of the pulmonary and sys temic circulations. But Cnsalpinus' work seems to have been lost sight of, and another, Hieronymus Fabricius, had the honor to open the next door that led to Harvey's triumph. Fabricius called renewed attention to the valves in the veins, but missed their real function, and, although he was Harvey's teacher, he was more of a Galenist than a modern.
It is to William Harvey's credit, not so much that he was the discoverer of the physi ology of circulation,— this, it can be seen from this brief recital, was of gradual accretion,— but that he was the first demonstrator of the process. He was the first physiological experi menter, and his work on the living animal has opened up to the world most of its priceless gifts in the field of medicine. It was by the faithful and prolonged study of many hearts of many animals that showed him that — " the motion of the heart consists in a certain universal tension, both of contraction in the line of its fibres. and constriction in every sense, that when the heart contracts it is emptied, that the motion which is in general regarded as the diastole of the heart is in truth its systole ' ; — that the true work of the heart is not that it sucked blood in, but that it drove blood out. Cmsalpinus guessed at this, or may be knew it, but Harvey proved it and, what is more, read the consequences. He saw clearly, then, the real function of the auricles and the ventricles and of their valves, and he applied the lessons of the lesser, or pulmonary circulation, to the greater, or systemic circulation, and thus rounded out the true natural history of the process. In his own words:
"I frequently and seriously bethought me, and long revolved in my mind, what might be the quantity of blood which was transmitted. in how short a time its passage might be effected, and the like; and, not finding it that this could be supplied by the juices of the ingested aliment without the veins on the one hand becoming drained, and the arteries on the other band becoming ruptured through the excessive charge of blood, unless the blood should somehow find its way from the arteries into the veins, and so return to the right side of the heart, I began to think might there not be a maim es it were in a circle. Now this I afterward found to be true;_ and I finally saw that the blood, forced by the action of the left ventricle into the arteries, was distributed to the body at large, and its several parts, in the same manner as it as sent to the lungs, impelled by the right ventricle into the pulmonary artery, and that it then passed through the veins and along the vena cave, and so round to the left ventricle in the manner already indicated, which motion we may be allowed to call circular." Thus clearly and forcefully he set forth in 1616—although his work did not appear until 1628—the true doctrine, and it is of interest to record that he lived to see it adopted practi cally by all scientists. Malphigi, in 1661, dem onstrated, by means of the microscope, the capillaries, thus filling out the last link in the chain of evidence.
Mechanics of closed circulatory system in man consists of the heart, arteries, capillaries and veins. The heart is a muscular pump which beats regu larly about 72 times a minute, thus forcing the blood with considerable velocity and force through the arteries and capillaries and back through the veins to enter the heart once more and so complete the circuit. The mam mal heart, as we have seen, has become a dou ble organ and each side consists of two cham bers, the auricles and ventricles.
The auricles are the smaller, less muscular portions of the heart, since their function is merely to receive the blood and transmit it to the ventricles. The walls of the left ventricle are four times the thickness of those of the right ventricle, since upon the left ventricle falls the work of propulsion for the entire systemic circulation, while the right ventricle has but to send the blood through the pul monary vessels. The direction of the course of the blood through the heart is maintained by the presence and arrangement of valves which guard the orifices between auricles and ventricles and opening of the aorta and of the pulmonary artery. The tricuspid valve, con sisting of three flaps of fibrous tissue, guards the right auriculo-ventricular opening, and the bicuspid or mitral valve, consisting of two flaps, guards the left. Near the base of attach ment these flaps are tough and able to withstand the pressure of the blood, while at the edges they are thin and delicate and yield to the force of the current. When the blood has passed into the ventricle they form by their perfect apposition an effective guard against return of the blood to the emptied auricle. The muscular attachments of the valves at the same time extend the diaphragm formed by their closing into the ventricle sufficiently to contract the ventricular chamber and so assist in expelling the blood. A backward eddy of the blood in the ventricle maintains the closure of the valves. Similar arrangement guards the proper closure of the aortic and pulmonary valves.