It's what vampires eat when they're feeling like Count Snackula. It's one of about five

bodily fluids that can change the MPAA rating of a movie. Running low? Head to your local

hospital and have them top you off.

Okay, so that's not actually how blood works and before you go in for a transfusion, there's

a whole lot of science to be done, because even the slightest mistake in this relatively

routine procedure can lead to a violent, horrifying death.

We know this, because we got to where we are today with a lot of trial and error by doctors

and unfortunate patients in the past.

The history of transfusion, according to the American Red Cross, actually goes all the

way back to the 17th century, with British physician William Harvey first describing

blood circulation in 1628. By 1665, another Englishman by the name of Richard Lower was

managing to keep dogs alive via infusions of fresh blood, and a year later, a fellow

named Jean Baptiste Denis conducted the first human blood transfusion.

And then things went off the rails. Lower experimented with giving people transfusions

of sheep's blood. When Denis tried it, though, the patient died, and in 1670, France banned

blood transfusions a ban that would remain in place for more than two centuries.

In the 1800's, though, doctors in England began using blood transfusions again, and

by the 1870's doctors in America were injecting people with milk yes, milk as a replacement

for blood. Within a few years, though, they replaced milk with saline, which was a lot

better, but still not as good as, you know, actual blood.

That all sounds crazy now, but thanks in part to those experiments, Austrian physician Karl

Landsteiner discovered the first three blood groups A, B, and O in 1901. In 1907, American

professor Ludvig Hektoen suggested that matching blood types might increase the odds of transfusion

recipients surviving longer, and the first matched transfusion was performed later that

year.

Matching blood types was a pretty enormous win for the medical community, and there's

a good reason we've never doubled back on the practice. Passing the wrong brand of blood

between patients is, as it turns out, about as healthy as jamming 2% into their arteries

like they did 150 years ago.

Here are the bare bones basics, as presented by the helpful folks at the Australian Academy

of Science: everybody has a blood type, which indicates what sorts of antibodies are in

their blood. Antibodies are special proteins that work as your body's pit bosses, identifying

problem customers like bacteria and viruses that make it into the works. A person with

type A blood possesses antibodies which target specific antigens, a person with type B blood

has a different set of antibodies.

If these antibodies notice something that doesn't look right, they go on the attack

lickety split including any foreign blood cells that show up with the wrong set of antigens

attached, which is why getting the wrong type blood is a really big problem.

"If hemolysis occurs in the blood or the serum, her red blood cells will explode. She will

die."

Yes, that's right: explode! See, when this happens, donor blood is rejected by the body

in a pretty dramatic way. The recipient's immune system will attack the outsider blood,

exploding the proteins in the foreign blood and sending the remains into the kidneys to

be separated from the rest of the gang. And the human kidney, while remarkable, isn't

set up to handle the sudden rush of dead blood cells that occurs when a large transfusion

goes wrong. Worst case scenario, they'll shut down entirely.

With that in mind, there's almost always a blood shortage at your local hospital, with

rare blood types frequently in short supply. Want to do your good deed for the day? Get

in contact with a blood bank and squirt out a pint for your fellow humans.

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