I have a whole chapter devoted to cholera in my last book about the history of sanitation. It’s a horrible disease and still, unfortunately, very much with us. It strikes in crowded places where drinking water gets contaminated. Nowadays the disease is treatable with oral rehydration and antibiotics, but in many places stricken by war or natural disaster, health workers lack the most basic supplies to help victims.

Cholera strikes your gut. No matter how much fluid you take in, somehow, it makes your intestines expel the fluid, rather than absorb it—like a power drill set on reverse, everything moves in the wrong direction. Victims acquire a powerful thirst and crave water, but their bodies expel the fluids rapidly (through vomiting and diarrhea) and their organs begin to shut down one by one, if left untreated. People usually die of dehydration.

Not to glorify an awful disease, but in a weird way, we have cholera to thank for our sanitation systems. It’s an ancient disease, long known and feared on the Asian subcontinent, but it wasn’t until 1832 that it travelled west, to Europe, the Middle East, and North America. As soon as people realized it was a water-borne disease, and that rich people as well as poor were dying from it, public officials began frantically implementing ways to clean up municipal water systems. And in my eyes, the true hero behind this movement was a doctor named John Snow.

 I grew up hearing about John Snow and the Broad Street pump from my father, who was in some ways a rather eccentric man

but who was a firm believer in the power of preventive approaches to many public health issues. While other kids were sitting on their parent’s knee being read Good Night Moon, I was hearing about how John Snow solved the cholera riddle, and how he convinced public officials to have the handle of the Broad Street Pump removed.

When a baby in Snow’s neighborhood in London fell ill with what turned out to be cholera, and the disease roared through the neighborhood killing people, he noted that workers across the street weren’t falling ill. If cholera were an air-borne disease, as so many believed back then, then why didn’t the inhabitants of the workhouse get cholera? (They didn’t because they had their own water supply.) Snow was an anesthesiologist to the Stars (he delivered Queen Victoria’s eighth baby using brand-new chloroform, which made her so happy, she knighted him). As an anesthesiologist, he understood the Law of Diffusion of Gases, which, in a nutshell, states that gas flows from an area of higher concentration to an area of lower concentration at a measurable rate  (sorry, chemists out there). Unfortunately Snow died before people had a chance to prove his theory. It wasn’t until ten years after his death that Robert Koch, that great epidemiologist, was able to isolate vibrio cholera under a microscope.