The four humors were black bile, red or yellow bile, blood and phlegm. The ancients believed that these substances ruled our personalities as well as our bodies. They divided all the possible character types into these four — melancholic, choleric, sanguine and phlegmatic — depending on which substance dominated that particular person.

Treatments for disease were designed to restore the balance among the humors, but what worked for one person might not work for another, which helped let practitioners off the hook if a "cure" didn't work. Purges like enemas and emetics were popular, and physicians often advised changes to a patient's diet or routine. Blood-letting was an especially durable cure for just about anything.

During labor, for example, "some women were bled to unconsciousness to counter delivery pains" or any other complications large or small, according to Peter Conrad's The Sociology of Health and Illness.

The acceptance of the germ theory finally put an end to humoral theory in mainstream medical thought.

Until then, a donor had to be on-site at the time of a blood transfusion.

Bernard Fantus

Dr. Fantus also coined the term "blood bank," in an article in the Journal of the American Medical Association that year that set out the hospital's methodology in clear, understandable terms.

Other institutions swiftly developed their own blood-storage facilities, and helped themselves to Fantus's catchy term as well.

Cook County's blood-storage innovation came at a critical time, just a few years before the start of World War II, when blood donated by people thousands of miles from the battlefronts would make the difference between life and death for a great many injured Allied soldiers.

Even early in the 20th century, a few minutes into any transfusion, blood would begin to clump together in the tube that was carrying it from donor to recipient, and the technician would have to start over. Letting blood sit in a container for any length of time was out of the question.

Richard Lewisohn

A number of researchers were working on the problem. The Belgian physician Albert Hustin, and the Argentinian doctor Luis Agote, both hit on the anticoagulant properties of sodium citrate in 1914, but the bad news was that the common compound was toxic in blood.

Dr. Richard Lewisohn of New York's Mount Sinai Hospital solved that problem with exhaustive experiments.  The German-born Lewisohn, who had trained at the excellent University of Freiburg, discovered the concentration at which sodium citrate could keep blood liquid without poisoning the transfusion recipient.

At first, it looked as if sodium citrate had a worrisome set of side effects, but Lewisohn proved that those were caused by infectious agents in poorly cleaned equipment. In the end, he showed that a diluted sodium citrate concentrate in blood, deployed with meticuously maintained needles and tubes, worked just about perfectly. In fact, it is still used.

Once the medical profession accepted Lewisohn's elegant solution to the clotting conundrum — and that took years — blood transfusions were transformed from a traumatic undertaking to the routine procedure they are today.

In 1916, just in time for World War I, researchers determined that sodium citrate allowed blood to be stored outside the body for up to two weeks.

One man undertook to change that, Alexis Carrel, a student in Lyons who was appalled by Carnot's death, in his hometown, while a number of physicians stood by and watched.

But consider the problem — repairing a tiny, elastic, living tube, part of a network of tubes of different sizes and functions, so that it would retain its ability to channel many gallons of blood every day, birth to death, without a hitch.

The story is that Carrel — Dr. Carrel by 1900 — studied with Marie-Anne Leroudier, one of the most proficient needlewomen in Lyons (her work was exhibited at the Columbian Exposition in Chicago in 1893), learning to make minute, uniform stitches. He developed a triangular system that allowed him to rapidly close up a vein or artery end-to-end without having the stitches adhere to the opposite wall, ushering in the birth of vascular surgery.

Carrel came to the University of Chicago in 1904, where his prodigious 21 months' work as an assistant to G. N. Stewart at the Hull Laboratory laid the groundwork for transplantation surgery. That work was the basis for Carrel's becoming the first scientist working in the United States to win the Nobel Prize for medicine, in 1912. Carrel soon moved on to the Rockefeller Institute for Medical Research in New York.

(Carrel's collaborator at the U. of C., Charles Claude Guthrie, was miffed that he was not included in the Nobel Prize. Guthrie possibly lost points with the Nobel committee for his subsequent experiments in St. Louis with head transplants.)

Carrel was a complicated man, compassion and curiosity mixed up with arrogance and resentment. He was a eugenicist — that is, he subscribed to the false science of "perfecting" the human race by eliminating traits judged to be inferior — and he was also an enthusiastic believer in the miracle cures at the shrine at Lourdes. At the time of his death in 1944, in Paris, he was working on a project for the collaborationist Vichy government.

The different blood types reflect the possible combinations of protein molecules called antigens, which are found on the surface of the red blood cells, and antibodies, which are in the plasma.

Just as when a disease invades the body, antibodies in the blood will attack certain antigens. This means that not all human blood is compatible.

If someone were to be given a transfusion with blood that contains antibodies that are hostile to antigens in his own blood, for example, he might die from a reaction that causes red blood cells to "clump," clogging blood vessels, or to "crack," leaking hemoglobin into the body with toxic effects.

O-negative blood lacks antigens, so people with O-negative blood have been considered "universal donors," whose blood would work harmlessly in anyone's body. It turns out that even some O-negative blood can react with some rare blood types, so the concept of the "universal donor" is now a conditional one, even though O-negative blood will still be given in an emergency if a patient's blood type is not known.

Conversely, people with AB-positive blood in general can receive any type of blood because that type does not contain antibodies that attack the A or the B antigens. (Type O blood lacks those antigens.)

The "plus" and "minus" in blood types refers to a particular antigen called "the Rh factor." Anyone can receive blood without the Rh factor, but only people with the Rh factor can safely receive blood that contains it.

If a pregnant woman needs a blood transfusion during or after labor — rare but possible — she will receive only blood that is compatible with her own — ideally her own specific blood type.

That began to solve the mystery of why some people who received blood transfusions were fine, while others became ill and often died.

Landsteiner subsequently discovered three of the four genetically determined blood groups or types, O, A and B. A couple of years later, Alfred von Decastello and Adriano Sturli, Landsteiner's colleagues in Vienna, identified a fourth blood group, AB. While about 30 blood types have been discovered, the original four essentially cover everyone.

In 1910, at the Heidelberg Institute for Experimental Cancer Research in Germany, Ludwig Hirszfeld and Emil von Dungern demonstrated that blood type is an inherited trait.

In the speech he made when he accepted the Nobel Prize in 1930 for his work, Landsteiner described the mystery blood presented, and how he and his fellow researchers unraveled its secrets.

In 1922, Landsteiner moved to the Rockefeller Institute of Medical Research in New York, where he discovered an extremely powerful blood antigen he called "the Rh factor."

Today, hospital personnel make sure they know a mother's blood type in case she needs a transfusion. She will also be tested for her Rh factor because it can pose a danger to her baby's well being.

His book, Blood: The Epic History of Medicine and Commerce, and the PBS documentary series it inspired, Red Gold, cover the waterfront on this vital component of life, and our relationship to it.

The PBS website has a great discussion guide that sums up the topic impressively, and includes a timeline of important developments in our evolving relationship with blood.

Even before we understood its function, humans invested blood with value and meaning. As Starr writes in an essay in the guide:

Blood: It’s strange that this most familiar of substances has always been so laden with feeling, so heavily freighted with mystery and symbolism. Consider the vocabulary: blood of our fathers; blood of Christ; the nation’s blood; lifeblood; blood brothers, blood sacrament, blood libel.…The history of blood involves not only medicine, but also culture and religion. It is a story of change — how a mysterious liquid became a global commodity and reflected the soul of each society that used it.

James Blundell, who like many physicians and researchers of the time also delivered babies, studied the short, disastrous history of transfusions and came to two far-reaching decisions — that only human blood should be used, and that it should be used for one purpose only, to replace blood. No curing mental illness, no altering personalities.

Blundell performed the first human-to-human transfusion in 1818, and went on to transfuse 10 patients over the next several years, half of whom died. Even with that dubious track record, transfusion took on new life, because Blundell's results weren't that bad, given the mortality picture of the time, according to Douglas Starr, author of Blood: An Epic History of Medicine and Commerce.

In 1873, Franz Gesellius, a Polish doctor, studied the records of all the transfusions he could find and determined that 56 percent  of the subjects had died. Critics began to attack transfusion as an attention-grabbing gimmick, and an dangerous one at that.

At the end of the 19th century, transfusion appeared to be headed the way of bloodletting and other quackery.

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."

Aeons ago, life on earth consisted of single cells suspended in the primordial sea. They took their nourishment directly from the surrounding waters, and excreted their waste products to be carried away, automatically, by the currents.

As more complicated animals evolved, the sea became private and internal in the form of blood, but it retained the original salts and the chemically useful pH, or acid-alkaline balance, of roughly neutral. When the first creatures slithered onto land, they took that inner sea with them.

The balances have changed slightly in the millions of years since then, but the individual cells of the human body are as dependent on the blood’s constancy as the first cells were on the never-changing sea.

From Shock-Trauma (1980), by Jon  Franklin and Alan Doelp