Lewis and Clark marked their trail with laxatives

By Finn J.D. John
January 26, 2025

AS LEWIS AND CLARK’S Corps of Discovery made its way across the continent to Oregon, the men (and woman) of the party probably weren’t thinking much about their place in history. So they weren’t taking any particular pains to document their every movement.

There were, however, some particular pains they were experiencing, as a result of a relentlessly low-fiber diet: Everyone was constipated, all the time.

Luckily, they had something that helped with that — a lot. The Corps of Discovery left on its journey with a trove of 600 giant pills that the men called “thunder-clappers,” which the soldiers and travelers used to jump-start things when they got bound up. And everyone used them pretty regularly.

And, strange as it seems, that fact is why we know several of their campsites along the way. The main active ingredient in “thunder-clappers” was a mercury salt, which is a pretty stable compound. Archaeologists simply have to search for dimples in the ground — which is what old latrine pits often end up looking like, hundreds of years later, after Nature has partly filled them in — and take samples of the dirt in them.

If it comes up with an off-the-charts reading for mercury, well, that’s a Corps of Discovery pit toilet — and the layout of the rest of the campsite can be extrapolated with considerable precision by consulting the military manuals they used to lay out their camps.

THESE PILLS WERE the pride and joy of Dr. Benjamin Rush, one of the Founding Fathers and a signer of the Declaration of Independence. Rush was also the man President Thomas Jefferson considered the finest physician in the republic.

In that opinion, Jefferson was probably alone, or at least in a small minority. Dr. Rush’s style of “heroic medicine” had caused his star to fall quite a bit by this time — especially after the Philadelphia yellow fever epidemic of 1793, when his patients died at a noticeably higher rate than untreated sufferers.

At the time, of course, very little was known about how the human body worked. Physicians were basically theorists, who made educated guesses and did their best.

The problem was, the education on which those educated guesses were based varied pretty wildly depending on what school you came from. Homeopathic physicians theorized that giving patients a tiny amount of something that mimicked their symptoms would stimulate the body to cure itself. Eclectic physicians sought cures from herbs and folk remedies. Hydropathic physicians believed hot and cold water, applied externally or internally, was all that was needed.

Dr. Rush wasn’t from one of these schools. He was from the school of mainstream medicine — also known as allopathic medicine (although that term is a perjorative today).

Allopathic medical theory, in the early 1800s, dated from the second century A.D., courtesy of a Roman doctor named Galen.

Galen theorized that the human body ran on four different fluids, which he called “humours”: Blood, phlegm, yellow bile, and black bile. All disease, he claimed, stemmed from an imbalance in these humours.

Thus, too much blood caused inflammation and fever; the solution was to let a pint or two out. Too much bile caused problems like constipation; the solution was to administer a purgative and let the patient blow out some black bile into a handy chamber-pot, or vomit up some yellow bile — or both.

These interventions sometimes helped, but most of the time they had little or no good effect. So by Rush’s time, a number of physicians were going on the theory that what was needed was a doubling-down on their theory — in a style of practice that they called “heroic medicine.”

If a sensible dose of a purgative didn’t get a patient’s bile back in balance, a “heroic” dose might. If a cup or two of blood didn’t get the fever down, four or five surely would.

You can imagine what the result of this philosophy was, when applied to an actual sick person.

“Some people have stated that the Lewis and Clark Expedition would have been better off if they had taken a trained physician along to care for the numerous problems that they encountered. I totally disagree,” says physician and historian David Peck. “I think a trained physician would have been overly confident and possibly would have been much more aggressive in their treatment of illnesses, often times to the detriment of the patient.”

In lieu of a trained physician, the Corps of Discovery’s leaders got some basic medical training, along with a bag full of the tools of allopathic intervention: lancets for bleeding patients, blister powder for inducing “heat,” opium products for relieving pain and inducing sleep — and purgatives.

Those purgatives are the heroes of our story today. They came in the form of beefy pills, about four times the size of a standard aspirin tablet, which Rush called “Dr. Rush’s Bilious Pills.” They contained about 10 grains of calomel and 10 to 15 grains of jalap.

Jalap, the powdered root of a Mexican variety of morning glory, is a natural laxative of considerable power.

And calomel ... ah, calomel. Calomel was the wonder drug of the age. Its chemical name is mercury chloride. In large doses (and they don’t get much larger than 10 grains, or 20 if a fellow takes two of them, as Dr. Rush recommended!) it functions as a savage purgative, causing lengthy and productive sessions in the outhouse and leaving a patient thoroughly depleted and hopefully in full restoration of his bile balance.

Calomel also was the only thing known to be effective against syphilis, which was always an issue with military outfits. Whether picked up from a friendly lady in a waterfront St. Louis “sporting house” before the journey, or from an equally friendly Native lady met along the way, syphilis went with soldiers like ice cold milk with an Oreo cookie.

When symptoms broke out, the patient would be dosed with “thunder clappers” and slathered with topical mercury ointments until he started salivating ferociously, which was a symptom of mild mercury poisoning but at the time was considered a sure sign that the body was purging the sickness out of itself.

And yes, a few of the men did end up needing treatment for syphilis. But everyone in the party needed a good laxative “on the regular” (sorry about that). Week after week, hunting parties went out and brought back animals to eat. The explorers lived on almost nothing but meat.

And this low-fiber diet had predictable results.

It had another result, too, which was less predictable — although highly convenient for later historians. The fact is, mercury chloride is only slightly soluble in human digestion. Plus, the reason it works is, it irritates the tissues of the digestive tract severely, causing the body to expel it just as fast as it possibly can before more damage can be done. So, most of the calomel in any given “bilious pill” gets blown out post-haste in the ensuing “purge.”

Then, once out of the body and in the earth, it lasts literally for centuries without breaking down or dissolving away.

So as Lewis and Clark and their crew made their way across the continent, and across Oregon, they were unknowingly depositing a trail of heavy-metal laxatives along the way — a trail that historians and scientists have been able to detect and use to document almost their every, uh, movement.

(Sources: Class lecture in History of American Medicine, October 2009, Univ. of Oregon; Or Perish in the Attempt: Wilderness Medicine in the Lewis and Clark Expedition, a book by David J. Peck published in 2002 by Farcountry Press; “Following Lewis and Clark’s Trail of Mercurial Laxatives,” an article by Marisa Sloan published in the Jan. 29, 2022, issue of Discover Magazine.)

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