Mammoth Cave

Nathaniel Kleitman was a faculty member of the Department of Physiology and made significant contributions to modern sleep research. In 1938, Kleitman conducted a sleep research study with graduate student Bruce H. Richardson in Mammoth Cave, Kentucky over the course of 32 days. During the experiment, Richardson and Kleitman adapted to a 28-hour day under “uniform conditions of temperature, illumination, and quiet of the cave.” Their experiment demonstrated that the human bodies roughly maintains a 24 hour temperature cycle even with the absence of external cues. Kleitman wrote Sleep and Wakefulness in 1939, an account of the Mammoth Cave study findings.

Here is some news footage from that time about the experiment.

Several pieces of furniture, including a bed, inside a dark cave.
Image from the Mammoth Cave Sleep Experiment

From: Box 33 Folder 3, Nathaniel Kleitman Papers.  University of Chicago Archives.

A man fiddles with medical equipment next to a bedridden man asleep.
Image from the Mammoth Cave Sleep Experiment

From the Photographic Archive, Special Collections Research Center, University of Chicago Library. Available at: Identifer: apf8-03489

Title page of Sleep and Wakefulness

Sleep and Wakefulness. Chicago, IL: The University of Chicago Press. 1939. Crerar: QP 425. K63