In 1938, just before World War II broke out, the city of London (population 9 million) only had eight pints of blood in storage ready for transfusion. For context, consider that the human body contains nine pints.

“By then, Britain knew to expect mass casualties, and it was pretty well expected that war would break out soon and London would be bombed,” says journalist Rose George. The men in power were preparing for war. They just weren’t thinking about the importance of blood in treating the wounded that were sure to come.

George is the author of Nine Pints: A Journey Through the Money, Medicine, and Mysteries of Blood. The book takes us through the cultural history of blood, as well as the scientific advances and endearing taboos. “If you think about it, it’s extraordinary that people give a living tissue out of their own body for a stranger,” George says. Less extraordinary is the dichotomy of good and bad blood and the way that blood in most medical contexts is seen as an “absolutely unquestioned good,” but menstrual blood leads to taboos that can deprive girls of their education.

The Verge spoke to George about the science of blood, the history of an important and underappreciated hematologist, the harm of menstrual taboos, and whether anything is changing.

This interview has been lightly edited for clarity.

Let’s start by talking a little bit about the cultural history of blood. Before our modern understanding of blood, what did people think this substance was? And how did we get to the practice of leeches and bloodletting?

Well, there was the humoral theory of the body, which is the idea that the body has four humors: phlegm, yellow bile, black bile, and blood. These four liquids governed your body, and you could get rid of bile and phlegm quite straightforwardly by, for example, vomiting. So I guess they’re thinking that if you get rid of the other humors of the body, you should get rid of blood as well, so that’s how bloodletting came about.

In terms of what blood was, it was obviously a very powerful substance. Most of the time when blood was seen, apart from bloodletting, somebody died afterward. If you saw blood spilled, you tended to see someone who was gravely injured and probably dying. It was understood that it had to do with life and life force.

If you look at myths of the Gorgon Medusa, in addition to having a head full of snakes, she had different types of blood on her right and left side, and one side was considered good and bad. To me, that’s a really interesting way of summing up pre-Enlightenment views of blood. It could be good or bad. It was a two-faced thing. And that’s still the case, isn’t it? Blood can save our lives, and it can kill us as easily.

Turning more to the science side, what are some of the advances we’ve seen in the study of blood and its properties? We see, for example, people hawking young blood as a treatment for aging.

Right. The claims of young blood are unproven, and it’s pretty hard to believe that two liters of an infusion of plasma can cure dementia. When it comes to advances in blood, one fascinating thing I learned is that blood is such an astonishing substance that we can’t quite replicate it. Well, we can grow blood cells, but it’s really hard, and it’s not as cheap or effective as the stuff coming out of someone’s arm.

Another thing is that there’s quite a strong cohort of trauma surgeons who are going back and investigating the use of whole blood. Nowadays, people commonly do something called component therapy, which is splitting up blood into, say, red blood cells or plasma and platelets, and you mix and match. But even if you put everything back together, it still doesn’t work as well as whole blood before it’s been separated. We can replicate a lot of things, but there’s something that is missing.

Plus, the idea used to be that if someone had severe trauma and was suffering from shock, you’d give them liquids and hope that would tide them over. But that’s actually just diluting the remaining blood in the body and making it harder for them to get oxygen. So now, pretty eminent trauma surgeons and hospitals are trialing the idea that, for a trauma patient who is severely hemorrhaging, perhaps what’s going to help them best is warm, fresh, whole blood instead of saline or fluid components.

I was fascinated by the part of your book about Janet Vaughan, who helped set up mass blood donation. Can you tell me about her?

Yes. I love talking about Janet Vaughan. Going back to the beginning of the 20th century, although blood would be transferred between humans, it was not at all done routinely or particularly safely. It wasn’t done en masse at all. It was very much ad hoc, and nothing enabled the mass transfer of blood.

Just before War World II in England, the entire storage of blood in London was eight pints. And that was in the maternity blood. Janet Vaughan was a hematologist and one of the few people who realized that in a war with mass casualties, you would need a lot of blood.

So she single-handedly arranged for her peers to come together and put together this system of blood donation. They would find blood donors, go to factories and get blood, and store it and transfer it to hospitals for the many expected victims of the Blitz. She pretty much did this on the fly and had no official sanction for a few months. Then a report was done at the end of the Second World War that says that the provision of blood was due to the foresight of many medical men, and she wasn’t honored in that way.

Speaking of blood transfusion, to what extent are we still suffering from blood shortages?

It depends where you’re looking. In places like the US and UK, there don’t tend to be many shortages, and they’re pretty good at planning. For example, after 9/11, there was a big rush to donate, and it was a really noble thing to do, but it wasn’t needed, and some of that blood was thrown away. But that’s not the case around the world. Just look at the number of women who die from postpartum hemorrhages from lack of blood, which is about 125,000 per year. Women should not be dying because of a lack of blood.

One of the questions you wanted to answer is why blood is considered so transformative, except when it comes to menstrual blood. You talk about traditions such as chhaupadi, when women are sent away when they’re on their period. What’s the history of these taboos?

If you look at how menstruation been written about in history, it’s been written about by men who have a pretty biased view. If we go back to the Romans, we look at Pliny the Elder who is cited in anything to do with menstruation because his views are so... remarkable. He thought menstrual blood was monstrously powerful, and a woman could walk through a field of corn and the ears of corn would drop off, sort of like a natural pesticide.

At other times in history, though, menstrual blood was seen as wonderful and miraculous. If you think about what I saw earlier, when people saw blood spills it meant death, but here were people spilling blood and living and giving rise to life. So sometimes, it was seen as a powerful substance, but that seems to have changed over time. The poisonous view of menstrual blood has prevailed, and it has so many knock-off effects. In places like Nepal and India, there’s real damage to girls and women who are isolated and deprived of free movement simply because they have a period. There are national holidays to have time off work to ritually cleanse in case they have looked at men while on their period. I wish that would stop.

Are these cultural attitudes toward blood changing, if at all? I know there are campaigns to end the tampon tax.

Things are changing. There’s the tampon tax, although if you look at it, why did it take until 2018 to notice there was one and to fight against it? And in the UK, apparently Gordon Brown couldn’t bear to say the word “tampon” in Parliament. Even though we in the US and UK might think we’re really advanced and have all this positive period walk, we have taboos; they’re just different. They look like the lack of honest advertising of lack of menstrual blood in any sanitary pad ad.

Still, in India, there was a demonstration the other day where a load of women linked arms to protest that they weren’t allowed into a temple because they were menstruating. I love that.