Joseph Lister came of age as surgery was being transformed. With the invention of anesthesia, operations could move beyond two-minute leg amputations that occasionally lopped off a testicle in haste. (True story.) But as surgeons poked and prodded deeper into the body, surgery only became more deadly.

It was the infections that killed people.

And it was Lister who first realized that germ theory has profound implications for medicine. In a new biography of Lister, Lindsey Fitzharris argues that the invention of antisepsis marks the true beginning of modern surgery. The Butchering Art: Joseph Lister’s Quest to Transform the Grisly World of Victorian Medicine takes its title from Lister’s own notes, where he writes of his love for “this bloody and butcherly department of the healing art.”

I spoke to Fitzharris about pus, Listerine, and the many things in between. An edited transcript of our conversation follows.

Sarah Zhang: A while ago, I was anxious about a medical thing, and my boyfriend tried to calm me down by telling me, “There is no better time in history to get surgery than now,” which was weirdly reassuring!

Lindsey Fitzharris: I think that will always be true.

Zhang: Yeah, though reading your book was a brutal, bloody reminder of how much worse it used to be.

Fitzharris: Before Lister, the operating rooms were filled to the rafters with hundreds of spectators who carry all this grime and dirt of everyday life in. This was not a sterile environment. Sometimes it was so crowded on the operating floor that they would have to clear it before the surgeons could actually begin the procedure. These weren’t necessarily medical students or surgeons or doctors themselves. Sometimes they were ticketed spectators who just came in to see the life-and-death struggle play out on the stage.

When you consider how controlled the operating room is today, it was just so wildly different before there was an understanding of germs. The surgeons, they wore their street clothes. They wore aprons that they never washed that they encrusted with blood.

Zhang: The bloody aprons were almost badges of honor.

Fitzharris: They were. There was one hospital that had a frock, an overcoat they hung in the operating theater and each surgeon would wear the same frock as a sort of a badge of honor, and it’s just encrusted with blood. Again, just no concept of germs or how unhygienic that would be. It was really just about the more that was encrusted on your apron, your frock, or your overcoat, the more seasoned you were as a surgeon.

And they never washed their instruments or their hands. The operating tables themselves were rarely washed down. These places became a sort of slow-moving execution for the patient because they would develop these postoperative infections that would kill them, sometimes within days, sometimes within months.

Zhang: A memorable phrase in your book comes from doctors praising the “laudable pus.” Why did 19th-century doctors believe that pus—which we now know is a sign of infection—was actually good?

Fitzharris: It really was because postoperative infections were so common. The rationale was it was somehow needed in order for the wound to heal. It was a good sign that wounds were suppurating.

Joseph Lister (Wellcome Library, London)

Zhang: How does Lister start putting the pieces together on what is causing infections?

Fitzharris: There are doctors and surgeons who are starting to question the existing disease explanation, which is miasma theory—that is, disease is caused by bad smells. There’s discontent in this period. It’s a growing problem in hospitals. People are dying en masse. The solution that is thrown out there is that they should burn these hospitals down and start anew because the crisis is growing.

Ignaz Semmelweis in Austria noted that when doctors were going from the dead house to the dissection room and then birthing women in labor and delivery, they had higher frequencies of mortality rates, because, he reckoned, they were transferring something from the dead house to these women. But he still didn’t understand it was germs. That came later—that’s what Lister’s contribution is. He takes Louis Pasteur’s germ theory and he marries it to medical practice with antisepsis. And he is also the one who ultimately ends up convincing the medical community to adopt antisepsis.

Zhang: The antiseptic Lister ends up using is carbolic acid, which is extracted from coal tar, of all places. How did he think to use something like that on open wounds?

Fitzharris: He comes across an article in the newspaper that carbolic acid was being used in Carlisle [England] to kill the smell of the sewage in that area. He thought if it was good enough to kill the rotting smell of the sewage, then it might just do the trick on wounds.

He begins to experiment. He decides that the air around the patient also needs to be sterilized. He creates this amazing contraption which was known as the donkey engine. It was like two big bellows, and it was on a tripod, and you would press on it, and the carbolic acid would spray into the air. He didn’t realize that the air actually didn’t need to be sterilized, and he gives up the donkey engine in later years.

It was funny because he had to carry this contraption around with him, and it was said that people in Glasgow would find him very amusing because he would have to sit at the bottom of the carriage because this thing was so big and took up so much room. You’d see Lister going around this city in this contraption to perform operations in people’s homes.

Joseph Lister’s carbolic acid–spraying machine (Science Museum, London, Wellcome Images)

Zhang: What happened to carbolic acid? Why did it eventually fall out of favor?

Fitzharris: I don’t know exactly when it goes out of use, but a lot of surgeons who are working off Lister’s work in the late 19th century begin experimenting with different kinds of antiseptics, because carbolic acid was so corrosive. In fact, at the end of his life, it’s said that it was Lister’s habit to stick his hands into his pockets and to cover them because they were so corroded from using the carbolic acid for so long.

But Lister lives into his own fame, and there was this carbolic-acid popularity explosion and kinds of funny things happen. One of my favorites is these kits you could buy. You could go around with these kits to your neighbors and remove their hemorrhoids with carbolic acid, which seems incredibly dangerous.

And you have Listerine, which is a spin off of Lister's name. A man [named Joseph Lawrence] came to his lectures in Philadelphia when Lister came to America to convince surgeons of germs and was inspired to create Listerine.* It originally was a cure-all. It was actually used more commonly to cure gonorrhea until it was finally turned into mouthwash. One of the Johnson brothers of Johnson & Johnson was also in the audience when Lister came to America, and he began his company and first produced surgical antiseptic dressings.

Zhang: I wonder what Lister would think of bottles of Listerine today.

Fitzharris: He actually wasn’t very happy about it in his own time. He was a very humble man, and I think he felt very embarrassed, almost, by the outgrowth of all these products that came as a result of his triumphs.

Advertisement for a Joseph Lister lecture on the principles and practice of surgery (Wellcome Library, London)

Zhang: Lister ends up operating on his sister for breast cancer, which is a pivotal moment in your book. Her doctors originally do not want to operate because, at the time, it was so dangerous. But when you’re able to sterilize surgical wounds, surgery is not the last resort of the desperate. That's a really profound shift in how we think about surgery.

Fitzharris: This is the moment that surgery is ushered into the modern area. When a lot of people think of the history of surgery, they think of the dawn of anesthesia and the dawn of painless surgery. But actually, surgery became much more dangerous following the discovery of ether, because the surgeon was much more likely to pick up the knife and cut deeper into the body, but he was still unaware of germs.

Lister’s sister approached several other surgeons. This is right at the beginning of his development of antisepsis, and a lot of surgeons aren’t accepting germ theory at this point. They advise her not to go through with the mastectomy because it would be a gaping wound and she would likely die of some kind of infection. Lister is the only person who will do it. He performed this mastectomy on his dining-room table in his house in Glasgow.

Zhang: Obviously sterilization is still incredibly important in medicine, but we’re amid another revolution in how we think of bacteria with the microbiome. Did you have this in the back of your mind while writing about Lister, the way science can work in cycles?

Fitzharris: One of the biggest things I hope that people take from my book is that science is always evolving. What we know today is not necessarily what we know tomorrow, and we can be our biggest enemies. The biggest pushback from Lister came from his own colleagues. It’s difficult for us to understand, because germs seem obvious today, but here comes this young man saying that there are invisible creatures, and they’re killing your patients. It was a big leap.

*This article originally misidentified the creator of Listerine as one of the Johnson brothers. We regret the error.