One of the
most unusual cave stays ever recorded began on February
13, 1972, when 33-year-old French geologist Michel Siffre
climbed into Midnight Cave near Del Rio, Texas. He
didn’t, come out again until September 5th. 
For six
months, Siffre was isolated in a large cave chamber
440-feet from the entrance. His furnishings were sparse: a
tent erected on a wooden platform was equipped with a bed,
table and chair, and various machines for science
experiments. The chamber was also stocked with frozen food
and almost 800 gallons of water.
Perhaps more
important is what the chamber did not contain: there were
no calendars or clocks or anything that would help him
establish the day or time.
By placing a person in an isolated environment,
without normal day and night cycles and without clocks or
timing devices of any kind, scientists hoped to determine
what natural body rhythms Siffre might develop.
This would help them predict the effects of long-term
missions on crews of nuclear submarines and spaceships.
Siffre was no
stranger to such experiments.
In 1962 he had stayed 63 days in a French alpine
cave, the longest time anyone had lived isolated
underground. That
experiment and others seemed to show that some people
begin to develop a 48-hour day, when all sense of time is
removed.
In Midnight
Cave, each one of Siffre’s “days” involved a set
morning routine. As
soon as he awakened, he reached for the nearby telephone
to let above-ground researchers know that he was awake.
Immediately, lights controlled by the researchers
were turned on, and Siffre began a four-hour regimen of
experiments. First he took his blood pressure, then a
series of mental, memory, and physical tests. 
He rode a
stationary bicycle for three miles and used a pellet gun
for five rounds of target practice.
When he shaved, he collected his whiskers for
experiments at the University of Minnesota.
During his
free time, he swept the guano-filled cave, trying not to
breath the dust which could cause him to develop a lung
disease. He
had planned to listen to music and read to fill the lonely
hours. Unfortunately, the damp cave environment caused his
stereo to malfunction and ever-present mildew to attack
his books.
By the end of
the first month, he was living a 26-hour cycle, though he
didn't know it at the time.
He simply stayed awake as long as he wanted and
called it a "night" when he felt tired.
He let the researchers know when he was ready to
sleep, and the lights were turned off.
He kept a diary that tracked his own days and
nights, but his calculations were not accurate.
For example, his Day 63 was really Day 77,
aboveground.
His diary also
recorded his thoughts and feelings. At first excited,
Siffre eventually became depressed by the total isolation.
He began to dislike the telephone, his one method of
communication with the outside world, because it
represented a freedom that he could not have.
His reaction
to cave mice demonstrated 
quite clearly how he changed in
the course of the experiment. During the first few weeks
underground, he could hear mice at "night" as he
prepared to sleep Their noises annoyed him, and he set
many traps for them. He caught eight, wiping out the
entire mouse colony.
Five months
into the experiment, however, he was starved for
companionship. On
Day 162, when he heard a noise and realized that another
mouse had come to visit, he was ecstatic.
"Another living creature exists in Midnight
Cave!" he wrote in his journal.
"If I trap this rodent, I will have a
companion."
For eight
days, Siffre tried to catch and tame the mouse.
He used a pea, then some jam, placed beneath a
propped-up casserole dish.
The mouse, named Mus by Siffre, was timid and
avoided capture. Finally,
Mus was caught, but with an unexpected result.
Siffre wrote:
My
patience prevails. After
much hesitation, Mus edges up to the jam.
I admire his little shining eyes, his sleek coat.
I slam down the dish.
He is captured! At last I will have a companion
in my solitude. My
heart pounds with excitement.
For the first time since ' entering the cave, I
feel a surge of joy.
Carefully I inch up the casserole.
I hear small squeaks of distress.
Mus lies on his side.
The edge of the descending dish apparently caught
him on the head. I
stare at him with swelling grief. The whispers die away.
He is still. Desolation overwhelms me.
Nine real days
later, on August 10th, the isolation part of the
experiment ended. Although
Siffre had to remain underground for almost four more
weeks for further tests, scientists could now visit him.
Obviously, he was overjoyed.
When he
finally emerged from the cave on September 5th, on Day
205, he found himself a changed man.
His eyesight had worsened, he had developed a
chronic squint, and some psychological troubles bothered
him. He
concluded that, even though he was able to develop a
28-hour day without the constraints of time, future space
travelers would have serious trouble adapting to
long-distance travel in confined areas.
Of course, they would not have the mildew or bat
guano that plagued Siffre.
And, he hoped, they might have the benefit of some
companionship.
SOURCE:
Siffre,
Michel. “Six Months Alone in a Cave,” National
Geographic (March 1975), 426-435.
