Investigations in blood

William Harvey's monumental achievement in discovering the circulatory system inspired two of his friends to dabble in the study of blood — Christopher Wren, the architect who designed St. Paul's Cathedral and other remarkable London buildings (Wren was an astronomer before he turned to architecture), and Robert Boyle, a pioneer in modern chemistry.

The men were all members of the Experimental Philosophy Club in Oxford, England, and admirers of the work of Francis Bacon, who advocated first-hand investigations into the natural world, rather than accepting long-held orthodoxies.

At the time, it was thought that the blood was impervious to anything that came from the outside world. Using a prototypical syringe made of a quill and a bladder, Wren and Boyle injected dogs with opium and other drugs, and showed that the dogs were affected — that they reacted to the opium, for example, by falling asleep.

These experiments inflamed the scientific community, and no end of creatures were injected with every kind of fluid, from urine to milk, sometimes with fatal results.

Richard Lower, an Oxford-trained doctor and protege of Wren and Boyle's, in 1665 decided to see what happened when he injected a dog with blood from another dog, connecting the two vein-to-vein. The experiment failed. The blood just pooled up in the connecting tube, Douglas Starr relates in his book, Blood: An Epic History of Medicine and Commerce.

Then, Lower tried tapping an artery in the donor dog, and this time the experiment worked. The stronger pressure from the arterial blood made for a successful transfusion, leading Lower to reason that "one Animal may live with the blood of another," Starr writes. Lower's experiments set off a frenzy for transfusions in England and, soon, in France.

Jean-Baptiste Denis, one of the French King Louis XIV's doctors, thought he might cure violent people of their rages by transfusing them with the blood of gentle animals like calves and sheep. At the time, people believed that blood contained a sterotypical set of characteristics of the creature that possessed it. For a while, it looked like Denis had had a stroke of genius, as one violent character in particular seemed for awhile utterly transformed.

Lower was furious, accusing Denis of stealing his work. Meanwhile, some human transfusion subjects began to die (blood being much more complicated than these men understood), including some high-profile patients of Denis. The French Parliament banned transfusions in 1670, followed by the British Parliament and eventually the pope.

That was the end of transfusions in Europe until the early 19th century.

Still, Starr writes, these early researchers "cracked the wall of humoral medicine, showing that the body was ruled not by vague humors but by chemicals, vessels and pumps."

The heart of the matter

The circulatory system is all about distributing oxygen around the body. The mighty heart — which never rests as long as we live — the 60,000 miles worth of blood vessels, and blood itself, all come down to this: Every cell in our bodies needs a fresh supply of oxygen every few minutes, or it will die. And so will we.

Diagram of the human heart

The human heart

The heart is at the center of the circulatory system, a hollow organ composed of muscle and connective tissue. In humans, the heart has four chambers — two atria or "entrances," and two ventricles or "bellies" — and weighs less than a pound.

The heart beats optimally about 70 times a minute throughout our lives, beginning within three weeks after conception, for a total of about 3 billion pulses in a lifetime of  80 years.

The heart pumps blood to the lungs, where it picks up its cargo of oxygen, and then on to the rest of the body.  Valves in the heart and the blood vessels ensure that blood travels in one direction only, away from the heart in the arteries, and toward the heart in the veins.

Red blood cells travel single-file through the capillaries, the fine vessels that connect the arteries and the veins, to deliver oxygen and other nutrients to the cells. Here the blood takes on waste, especially carbon dioxide, which it will deposit in the lungs for expulsion into the air.

A septum in the middle of heart keeps waste-filled blood returning from its journey through the body separate from oxygenated blood fresh the lungs.

Here in the heart, over and over, the journey begins again.

Image from http://commons.wikimedia.org