How do you follow a trail more than 200 years old, when even the maps they used uncertain? You look for specific historical deposits. And famed explorers of the Louisiana Purchase, Lewis and Clark, made some very unusual ones.

A year after President Thomas Jefferson purchased a lot of land from the French in 1803, he sent out Meriwether Lewis and William Clark to get a look at what exactly he’d bought. The two commanded an expedition that started out in St. Louis and made its way to the Pacific coast. Some parts of their trail are well-known, while others remained lost to historians for years. People knew roughly where Lewis and Clark made camp, but they couldn’t find the actual sites. And even if they happened to come across an old camp site, it was difficult to tell which actual campers had made this fire, or cut down that tree, or dug that latrine.

Eventually, researchers came across some information that helped clarify things... and that information came from their latrines. Lewis and Clark were fairly well-equipped and well-trained, even if only by the standards of the day. Given what those standards were, it’s surprising that they only lost one person during their trek. According to their own records, they bled people who were feverish, they gave purgatives to people who felt weak, and they administered potassium nitrate (a preservative substitute for salt) to people suffering from heat stroke and dehydration. They also brought along the wonder drug of the day, mercury chloride (otherwise known as calomel), as a pill, a tincture, and an ointment.

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Calomel was often used to treat those with syphilis (mercury does work against the bacterium that causes syphilis, but it takes out the host as well, so don’t try it at home) along with nearly everything else, including constipation. And an expedition that ate mainly the game they could catch along the way would have suffered from constipation regularly. In their journals, Lewis and Clark regularly make note of someone having to take one of Dr. Rush’s Bilious Pills (because constipation was thought to be caused by an excess of bile) and spending the day purging.

If you know that you and your men are going to spend a day expelling everything they’ve eaten for a week, you make sure to dig a latrine. Most of the mercury that the men ingested went out of the system again, which means that over a century later, historians and archaeologists were able to pin down where Lewis and Clark had stayed by testing old latrine contents for mercury.

Several sites have been discovered exactly this way. The most famous is Traveler’s Rest, in Montana. So if any Montanans are reading this, and have a weekend free, go out to your state park and, as you look around, savor the fact that you’ve been blessed with clever researchers and famous latrines. But maybe don’t drink the water near a Lewis and Clark campsite.

Top Image: Tony Hisgett