Harvey, Part 2

The Evolution of Modern Medicine
by William Osler

(Page 13 of 16)

Having grasped this first essential fact, that the heart was an organ for the propulsion of blood, he takes up in Chapters VI and VII the question of the conveyance of the blood from the right side of the heart to the left. Galen had already insisted that some blood passed from the right ventricle to the lungs - enough for their nutrition; but Harvey points out, with Colombo, that from the arrangement of the valves there could be no other view than that with each impulse of the heart blood passes from the right ventricle to the lungs and so to the left side of the heart. How it passed through the lungs was a problem: probably by a continuous transudation. In Chapters VIII and IX he deals with the amount of blood passing through the heart from the veins to the arteries. Let me quote here what he says, as it is of cardinal import:

"But what remains to be said upon the quantity and source of the blood which thus passes, is of a character so novel and unheard of that I not only fear injury to myself from the envy of a few, but I tremble lest I have mankind at large for my enemies, so much doth wont and custom become a second nature. Doctrine once sown strikes deeply its root, and respect for antiquity influences all men. Still the die is cast, and my trust is in my love of truth, and the candor of cultivated minds." Then he goes on to say:

"I began to think whether there might not be A MOVEMENT, AS IT WERE, IN A CIRCLE. Now this I afterwards 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 is sent through the lungs, impelled by the right ventricle into the pulmonary artery, and that it then passed through the veins and along the vena cava, and so round to the left ventricle in the manner already indicated."

The experiments dealing with the transmission of blood in the veins are very accurate, and he uses the old experiment that Fabricius had employed to show the valves, to demonstrate that the blood in the veins flows towards the heart. For the first time a proper explanation of the action of the valves is given. Harvey had no appreciation of how the arteries and veins communicated with each other. Galen, you may remember, recognized that there were anastomoses, but Harvey preferred the idea of filtration.

The "De Motu Cordis" constitutes a unique piece of work in the history of medicine. Nothing of the same type had appeared before. It is a thoroughly sensible, scientific study of a definite problem, the solution of which was arrived at through the combination of accurate observation and ingenious experiment. Much misunderstanding has arisen in connection with Harvey's discovery of the circulation of the blood. He did not discover that the blood moved, - that was known to Aristotle and to Galen, from both of whom I have given quotations which indicate clearly that they knew of its movement, - but at the time of Harvey not a single anatomist had escaped from the domination of Galen's views. Both Servetus and Colombo knew of the pulmonary circulation, which was described by the former in very accurate terms. Cesalpinus, a great name in anatomy and botany, for whom is claimed the discovery of the circulation, only expressed the accepted doctrines in the following oft-quoted phrase:

"We will now consider how the attraction of aliment and the process of nutrition takes place in plants; for in animals we see the aliment brought through the veins to the heart, as to a laboratory of innate heat, and, after receiving there its final perfection, distributed through the arteries to the body at large, by the agency of the spirits produced from this same aliment in the heart." There is nothing in this but Galen's view, and Cesalpinus believed, as did all his contemporaries, that the blood was distributed through the body by the vena cava and its branches for the nourishment of all its parts. To those who have any doubts as to Harvey's position in this matter I would recommend the reading of the "De Motu Cordis" itself, then the various passages relating to the circulation from Aristotle to Vesalius. Many of these can be found in the admirable works of Dalton, Flourens, Richet and Curtis. In my Harveian Oration for 1906 I have dealt specially with the reception of the new views, and have shown how long it was before the reverence for Galen allowed of their acceptance. The University of Paris opposed the circulation of the blood for more than half a century after the appearance of the "De Motu Cordis."

To summarize - until the seventeenth century there were believed to be two closed systems in the circulation, the natural, containing venous blood, had its origin in the liver from which, as from a fountain, the blood continually ebbed and flowed for the nourishment of the body; the vital, containing another blood and the spirits, ebbed and flowed from the heart, distributing heat and life to all parts. Like a bellows the lungs fanned and cooled this vital blood. Here and there we find glimmering conceptions of a communication between these systems, but practically all teachers believed that the only one of importance was through small pores in the wall separating the two sides of the heart. Observation - merely looking at and thinking about things - had done all that was possible, and further progress had to await the introduction of a new method, viz., experiment. Galen, it is true, had used this means to show that the arteries of the body contained blood and not air.

The day had come when men were no longer content with accurate description and with finely spun theories and dreams. It was reserved for the immortal Harvey to put into practice the experimental method by which he demonstrated conclusively that the blood moved in a circle. The "De Motu Cordis" marks the final break of the modern spirit with the old traditions. It took long for men to realize the value of this "inventum mirabile" used so effectively by the Alexandrians - by Galen - indeed, its full value has only been appreciated within the past century. Let me quote a paragraph from my Harveian Oration. "To the age of the hearer, in which men had heard and heard only, had succeeded the age of the eye in which men had seen and had been content only to see. But at last came the age of the hand - the thinking, devising, planning hand, the hand as an instrument of the mind, now re-introduced into the world in a modest little monograph from which we may date the beginning of experimental medicine."

Harvey caught the experimental spirit in Italy, with brain, eye and hand as his only aids, but now an era opened in which medicine was to derive an enormous impetus from the discovery of instruments of precision. "The new period in the development of the natural sciences, which reached its height in the work of such men as Galileo, Gilbert and Kepler, is chiefly characterized by the invention of very important instruments for aiding and intensifying the perceptions of the senses, by means of which was gained a much deeper insight into the phenomena than had hitherto been possible. Such instruments as the earlier ages possessed were little more than primitive hand-made tools. Now we find a considerable number of scientifically made instruments deliberately planned for purposes of special research, and as it were, on the threshold of the period stand two of the most important, the compound microscope and the telescope.

About the Author

William Osler (1849 - 1919) was a Canadian physician. He has been called one of the greatest icons of modern medicine and the Father of Modern Medicine (which is what he himself considered Avicenna to be).