The Circulation of the Blood. Biology

Rather more subtle than the matter of the appearance and arrangement of the component parts of the body, which is the subject matter of anatomy, is the study of the normal functioning of those parts. The latter is physiology. The Greeks had made little progress in physiology and most of their conclusions were wrong. In particular, they were wrong about the functioning of the heart.

The heart is clearly a pump; it squirts blood. But where does the blood come from, and where does it go? The early Greek physicians made their first error in considering the veins to be the only blood vessels. The arteries are usually empty in corpses and so these were thought to be air-vessels. (The very word "artery" is from Greek words meaning "air duct.")

Herophilus, however, had shown that both arteries and veins carried blood. Both sets of blood vessels are joined with the heart and the matter would then have solved it- self neatly if some connection between veins and arteries had been found at the ends away from the heart. However, the most careful anatomical investigation showed that both veins and arteries branched into finer and finer vessels until the branches grew so fine they were lost to sight. No connection between them could be found.

Galen, therefore, suggested that the blood moved from one set of vessels to the other by passing through the heart from the right half to the left. In order to allow the blood to pass through the heart, he maintained there must be tiny holes passing through the thick, muscular partition that divided the heart into a right and left half. These holes were never observed, but for seventeen centuries after Galen, physicians and anatomists assumed they were there. (For one thing, Galen had said so.)

The Italian anatomists of the new age began to suspect that this might not be so, without quite daring to come out in open rebellion. For instance, Hieronymus Fabrizzi, or Fabricius (1557-1619), discovered that the larger veins possessed valves. He described these accurately and showed how they worked. They were so arranged that blood could flow past them toward the heart without trouble. The blood, however, could not flow back away from the heart without being caught and trapped in the valves.

The simplest conclusion from this would be that the blood in the veins could travel in only one direction, toward the heart. This, however, interfered with Galen's notion of a back-and-forth motion and Fabricius only dared go as far as to suggest that the valves delayed (rather than stopped) the backward flow.

But Fabricius had a student, an Englishman named William Harvey (1578-1657), who was made of sterner stuff. After he returned to England, he studied the heart and noted (as had some anatomists before him) that there were one-way valves there, too. Blood could enter the heart from the veins, but valves prevented blood from moving back into the veins. Again, blood could leave the heart by way of the arteries but could not return to the heart because of another set of one-way valves. When Harvey tied off an artery, the side toward the heart bulged with blood; when he tied off a vein, the side away from the heart bulged.

Everything combined to show that the blood did not ebb and flow but moved in one direction perpetually. Blood flowed from the veins into the heart and from the heart into the arteries. It never backtracked.

Harvey calculated, furthermore, that in one hour the heart pumped out a quantity of blood that was three times the weight of a man. It seemed inconceivable that blood could be formed and broken down again at such a rate. Therefore, the blood in the arteries had to be returned to the veins someplace outside the heart, through connecting vessels too fine to see. (Such invisible vessels were no worse than Galen's invisible pores through the heart muscle.) Once such connecting vessels were assumed, then it was easy to see that the heart was pumping the same blood over and over again—veins/ heart/ arteries/ veins/ heart/ arteries/ veins/ heart/ arteries. . . . Thus it was not surprising it could pump three times the weight of a man in one hour.

In 1628, Harvey published this conclusion and the evidence backing it in a small book of only seventy-two pages. It was printed in Holland (and filled with typographical errors) under the title De Motu Cordis et Sanguinus ("On the Motions of the Heart and Blood"). For all its small size and miserable appearance, it was a revolutionary book that fitted the times perfectly.

Those were the decades when the Italian scientist, Galileo Galilei (1564-1642), was popularizing the experimental method in science and, in so doing, completely destroyed Aristotle's system of physics. Harvey's work represented the first major application of the new experimental science to biology and with it he destroyed Galen's system of physiology and established modern physiology. (Harvey's calculation of the quantity of blood pumped by the heart represented the first important application of mathematics to biology.)

The older school of physicians inveighed bitterly against Harvey, but nothing could be done against the facts. By the time of Haney's old age, even though the connecting vessels between arteries and veins remained undiscovered, the fact of the circulation of the blood was accepted by biologists generally. Europe had thus stepped definitely and finally beyond the limits of Greek biology.

Haney's new theory opened a battle between two opposing views of life, a battle that has filled the history of modem biology, and one that is not entirely settled even yet.

According to one major view of life, living things are considered essentially different from inanimate matter so that one cannot expect to leam the nature of life from studies on nonliving objects. In a nutshell, this is the view that there are two separate sets of natural law: one for living and one for nonliving things. This is the "vitalist" view.

On the other hand, one can view life as highly specialized but not fundamentally different from the less intricately organized systems of the inanimate universe. Given enough time and effort, studies of the inanimate universe will provide enough knowledge to lead to an understanding of the living organism itself, which, by this view, is but an incredibly complicated machine. This is the "mechanist" view.

Harvey's discovery was, of course, a blow in favor of the mechanist view. The heart could be viewed as a pump and the current of blood behaved as one would expect a current of inanimate fluid to behave. If this is so, where does one stop? Might not the rest of a living organism be merely a set of complicated and interlocking mechanical systems? The most important philosopher of the age, the Frenchman, Rene Descartes (1596-1650), was attracted by the notion of the body as a mechanical device.

In the case of man, at least, such a view was dangerously against the accepted beliefs of the day, and Descartes was careful to point out that the human body-machine did not include the mind and soul, but only the animal-like physical structure. With respect to mind and soul he was content to remain vitalist. Descartes made the suggestion that the interconnection between body and mind-soul was through a little scrap of tissue pendant from the brain, the "pineal gland." He was seduced into this belief by the mistaken feeling that only the human being possessed a pineal gland. This quickly proved not to be so. Indeed the pineal gland in certain primitive reptiles is far better developed than in the human.

Descartes' theories, though possibly wrong in details, were nevertheless very influential, and there were physiologists who attempted to hammer home the mechanist view in elaborate detail. Thus, the Italian physiologist, Giovanni Alfonso Borelli (1608-79), in a book appearing the year after his death, analyzed muscular action by treating muscle-bone combinations as a system of levers. This proved useful and the laws that held for levers made of wood held exactly for levers made of bone and muscle. Borelli tried to apply similar mechanical principles to other organs, such as the lungs and stomach, but there he was less successful.