Not your type?

The four basic blood groups or types, in order of frequency from most common to rarest, are O, A, B, and AB. Blood type is determined by "alleles," or possible types of a gene, that we inherit from our parents.

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.

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."

Simon Flexner

After Simon Flexner dropped out of the sixth grade in Louisville, Ky., in the 1870s, his father, Morris, arranged a tour for him of the town jail, warning that if he didn't straighten out, that was where he would wind up.

But after Simon, the fourth of nine children, nearly died of typhoid fever at the age of 16, he found his passion — infectious diseases.

Simon Flexner

Simon Flexner

Flexner went to work as an apprentice in his brother Jacob's pharmacy, where he learned to use a microscope. Doctors he knew from the store gave him tissue samples for his self-directed studies in histology, the study of microscopic structures in tissues, and pathology.

At 26, he earned his medical degree from the two-year program at the University of Louisville. His younger brother Abraham, a recent graduate of  Johns Hopkins University, arranged for Simon to study pathology there under William Henry Welch, who was helping to bring the scientific method to American medicine.

Flexner became a microbe hunter extraordinaire, helping to suss out the causes of meningitis among Maryland coal miners, bubonic plague in San Francisco's Chinatown, and a common dysentery that is now known as Flexner's bacillus. He also played a critical role in the conquest of polio.

In 1902, Flexner became the head of the new Rockefeller Institute for Medical Research, and this is where the birth story intersects his own. Flexner assembled an amazing team of scientists that included Alexis Carrel, Peyton Rous and Karl Langsteiner who, among other achievements, brought blood transfusion to reality.

The basics of birth safety

What do women need when birth becomes difficult? The Averting Maternal Death and Disability program has identified a handful of intervention capabilities that should be in place for emergencies wherever babies are born.

These "signal functions" include having personnel on hand who are trained to administer drugs by injection -- antibiotics, anticonvulsants and "oxytocics," which can start or speed labor -- manually remove the placenta and other "products of conception" not leaving the body spontaneously, and perform assisted vaginal delivery -- with forceps, for example.

AMDD, a major initiative of the Mailman School of Public Health at Columbia University in New York City,  has worked with UNICEF and other partners for 20 years to bring down maternal-mortality rates in the developing world.

Its directive, issued in 1997, cites two additional interventions that might be necessary to save lives -- Caesarean section and blood tranfusion. These two go beyond the basics of a birth center -- in some parts of the world they are strictly wish-list items -- but they can often make the difference between life and death, as they did in our case.

AMDD doesn't include anesthesiology in its signal functions, although surgery is difficult without it.

We in the United States might view these interventions as humdrum, or even as irksome or worse if they become part of our own birth story, but behind the development of each one of them are amazing tales.