Two stone rooms stand beside Broadway inside Mammoth Cave. Their walls are thick, roughly fitted and open at the top where canvas roofs once separated sick patients from the darkness above them.
They are the remains of one of Kentucky’s strangest medical experiments.
During 1842 and 1843, Louisville physician and cave owner John Croghan brought people suffering from tuberculosis underground. He believed Mammoth Cave’s steady temperature and unusual atmosphere might slow the disease. Patients lived beyond the rhythms of daylight while fires and oil lamps burned in the passage.
The experiment failed. That much is clear.
Nearly every number attached to it is not.
National Park Service sources variously describe 10, 13, 15 or 16 patients. One says five died inside the cave. Another says seven. A third says only that “some” died there. The structures are counted differently too.
The familiar story usually solves this problem by choosing one version and telling it with confidence. The historical record requires something better: explain why the experiment made sense to Croghan, recover what patients and workers said, and leave the disputed totals visibly disputed.
The count problem
The newest National Park Service feature says Croghan invited 16 patients underground in the winter of 1842. It also quotes an enslaved server named Alfred recalling 15 people at mealtime. That page reports five deaths inside Mammoth Cave.
The park’s master timeline tells a different story. It identifies Dr. William J. Mitchell as the first of 10 patients and places his entry in May 1842, months before the autumn opening described elsewhere. It says some patients died in the cave and all ultimately died of the disease.
An NPS cultural-landscape history gives 13 patients and seven deaths.
These are not small differences produced by rounding. They suggest that later summaries drew from different stages of the experiment, different definitions of who counted as a patient, or historical sources that were already incomplete. A person who entered for observation in May may not appear in a list of winter residents. Alfred’s memory of 15 diners may describe the group on one occasion, not a complete admissions ledger.
No authoritative roster located for this article reconciles the versions. The honest answer is therefore a range: public institutional accounts place the number of patients between 10 and 16, and reported deaths inside the cave between five and seven.
The uncertainty does not make the hospital a legend. It reveals how quickly people can disappear behind a famous number.
Why Croghan thought cave air might help
John Croghan purchased Mammoth Cave and about 1,600 surrounding acres from Franklin Gorin in 1839 for $10,000. The transaction included enslaved people who worked at the cave.
Croghan was a physician. He also suffered from tuberculosis, then commonly called consumption. The disease attacked the lungs, produced wasting and killed enormous numbers of people. In 1842, physicians did not know that a bacterium caused it. Robert Koch would not identify the tubercle bacillus until 1882, and effective antibiotic treatment lay much farther in the future.
Medicine offered regimens rather than cures: rest, diet, travel and changes of climate. In that setting, Croghan’s reasoning was hopeful but not incomprehensible.
Visitors reported that Mammoth Cave’s air felt invigorating and that long underground walks produced surprisingly little fatigue. The cave held a nearly constant temperature. Timber and animal remains appeared to decay slowly. If ordinary corruption seemed suspended underground, perhaps disease might be slowed there too.
Croghan imagined more than a small trial. As patients appeared to improve at first, he drew plans for a larger underground hotel or sanitarium capable of receiving people who came for the cave’s climate.
Initial improvement, however, was an impression—not evidence of a cure.
Building a hospital underground
The patients’ residence stood along the broad passage now called Broadway. Here too, the surviving summaries disagree. The current NPS feature describes two stone cabins and eight wooden buildings. The National Register documentation says 12 huts were built in all. Both agree that only the two stone structures survive.
Enslaved people constructed the buildings. Their work made Croghan’s experiment possible, though older versions often reduce them to anonymous labor or omit them entirely. NPS research also states that enslaved workers prepared some food and carried meals from outside the cave.
Alfred is the one worker whose voice appears prominently in the surviving interpretation. He remembered standing on a rock and blowing a horn to call the patients to dinner. There were 15 of them, he said, and advanced illness had left them looking like “a company of skeletons.”
The sentence is often repeated for its macabre force. It also records labor. Alfred moved between hotel, kitchen and underground settlement, keeping time and serving people whose treatment depended on his work.
The wooden patient rooms measured about 12 by 18 feet and used plank floors and canvas roofs. The stone rooms had heavy limestone walls. Watches had to be synchronized with the outside world because daylight could not mark the hour.
Patients walked, ate and attempted to live by a schedule inside a place that never became morning.
A patient’s view
H.P. Anderson’s December 21, 1842 letter is one of the most valuable surviving records because it comes from a patient rather than a later guide or promoter.
Anderson did not describe an obvious nightmare or miracle. He wrote like someone participating in an unfinished experiment. Much remained to be done, he acknowledged, before the cave could be comfortable or its virtues fairly tested. He called the residents pioneers and imagined that later generations might benefit from what they endured.
The optimism matters. Patients were not simply props carried into a physician’s folly. At least some understood themselves as participants in a serious search for relief.
But the conditions worked against diseased lungs. Lard-oil lamps and a large fire produced smoke and ash in an underground passage. Vegetation brought down to brighten the settlement withered. The darkness isolated patients from ordinary life. The cave’s dampness and the products of constant burning made breathing no easier.
According to the NPS account, Anderson asked to leave and became the only patient Croghan permitted to return to the surface before the experiment ended. That detail comes through later institutional reconstruction and should not be expanded into invented conflict.
By March 1843, the last patient had left.
Death underground and “Corpse Rock”
How many died inside Mammoth Cave remains unsettled. The strongest responsible phrasing is not “exactly five” or “exactly seven,” but that multiple patients died during the experiment and current NPS histories disagree on the total.
The current park feature says five bodies were laid on what is now known as Corpse Rock. The words “now known” are essential. They do not establish that patients, Alfred or Croghan used the name in 1842.
Later tourist and paranormal retellings often turn the rock into a gothic morgue and the huts into a haunted hospital. That imagery compresses sick people, enslaved workers and medical uncertainty into scenery.
The documented history is dark enough. People entered Mammoth Cave because tuberculosis had left them few options. Some died there. Others emerged without a cure and later died from the same disease. Croghan himself died of tuberculosis in 1849.
No ghost story is needed to make the stone rooms consequential.
What survives
The wooden rooms were dismantled. Two stone structures remain within the Mammoth Cave Historic District, their canvas roofs gone. They are preserved inside a living cave system rather than abandoned on an accessible ruin site.
Visitors can see the tuberculosis huts only through authorized National Park Service access, including tours whose routes pass Broadway. The protected cave should never be entered outside official tours.
The huts are sometimes described as an underground hospital. That phrase is useful, but it can suggest an institution more complete than the evidence shows. This was a small experimental settlement: a physician, a shifting group of seriously ill residents, buildings constructed and serviced through enslaved labor, and an environment expected to heal because medicine had not yet learned what caused the disease.
What the experiment establishes
Croghan’s patients were not cured. Mammoth Cave’s climate did not stop tuberculosis. The smoke, darkness and damp conditions likely made life harder for already damaged lungs.
Yet the experiment deserves more than a verdict of foolishness. It shows what desperation can make reasonable before the mechanism of a disease is known. It also shows how historical memory favors dramatic totals even when the sources do not agree.
Ten patients or 16. Five deaths or seven. Those contradictions should send us back toward the people, not away from them.
Anderson left a patient’s cautious hope. Alfred left the sound of a horn calling people to dinner. Enslaved workers built rooms beneath a property they did not own. Two stone walls remain where the theory met the cave.
Tell the story. Keep the count open.
Further viewing
The National Park Service’s short program with Ranger Autumn provides direct interpretation of the surviving tuberculosis huts: Tuberculosis in Mammoth Cave. The following independent Historic Tour video supplies broader visual context for the authorized visitor route through Mammoth Cave; it is not evidence for the disputed patient and death counts.
Sources and further reading
- National Park Service: Tuberculosis in Mammoth Cave
- National Park Service: Mammoth Cave timeline
- National Park Service: Mammoth Cave cultural landscape
- National Register of Historic Places: Mammoth Cave Historic District
- The Filson Historical Society: William Croghan family papers
- “Groping for Health in Mammoth Cave,” Filson Club History Quarterly, October 1946.
- W. Stump Forwood, An Historical and Descriptive Narrative of the Mammoth Cave of Kentucky (1870).
- Horace Carter Hovey, Guide Book to the Mammoth Cave of Kentucky (1895).
Editorial note
No outreach interview was conducted. Current National Park Service materials conflict on patient, death and structure totals; those discrepancies are preserved rather than silently resolved.