In 1945, Brigadier Sir Cedric Stanton Hicks (1982-1976) led a party of physiologists into the Central Australian bush to study the famed capability of the native Aborigines to sleep the night away without clothes or blankets but nonetheless in comfort. The brigadier human physiologist found it difficult to get the desired measurements because the Aboriginals refused to submit to the rectal thermometers. So, another decade would pass before the mystery of camping out in the buff on those cool 39 F nights in the Australian outback.
Enter the plant and animal physiologist Per Scholander. With three colleagues from the University of Adelaide, themselves unafraid of the rectal thermometer, Scholander negotiated with 6 Aborigines, likewise fearless, and setout for the Outback. Global warming had yet to warm the Australian nights. The ten instrumented subjects on canvas cots tried to sleep. Note that this is not a double-blind study as the investigators were themselves subject to the same indignity suffered by the native Australians.
In little time, the core body temperatures of the physiologists began to drop and quickly shivering set in and metabolic rates increased by 30%! Both skin and body core temperatures declined.
The Aboriginal subjects in the study fared differently. They did not shiver. Their metabolic rate remained unchanged. Core body temperatures and skin temperatures both fell below that of the scientists. They slept through it all. The outward flux of energy from the core of the body was impeded by an insulation of a more robust layer of subcutaneous adipose. The skin cooled. The rectal temperatures (body core) fell but the subcutaneous layer dampened the overall loss of heat from the body. In the subcutaneous layer one finds where the hot and cold nerve ending receptors. The rapidity of impulses to the brain reflects the rate of temperature change. The extra adipose insulation retards heat loss and calms those nerve endings. Naked slumber ensues.
In contrast, the naked scientists produce 30% more heat by their shivers, which is then the lost to the cold night air. Their nerve endings sensing heat loss, scream -- I can’t sleep like this!
A note on Sir Stanton Hicks -- He earned his Brigadier rank in the Australian Army’s catering division in WWII. It is my pleasure to report to you that he wrote a book in 1972 titled “Who Called the Cook a Bastard?
Per Scholander, invented a “pressure bomb” used to measure the pressure needed to overcome the free energy of the water in the xylem of twigs. He traveled the world in search of interesting water tension problems to study.
Ona, Yahgan and Alacaluf native South Americans of the Tierra del Fuego. The typical weather forecast: Rain mixed with snow winter and summer. Cloudy with little sun. Winds sweep the barren rocky landscape all the time. After all, Tierra del Fuego is in the roaring forties and just north of the frantic fifties. Who needs clothes in a paradise like this?
Darwin was much taken by native people and their naked ways. Darwin collected three of these natives from the Alacaluf tribe (I think) and gave them bunks on the Beagle. They were gussied up with proper English clothes and put on the cocktail circuit such as it was in those days. Some three years later these fellows were returned to their homeland. Anyway, just how were they able to thermoregulate? Following Scholander’s techniques, nine Alacaluf’s Indians were found and instrumented rectally. They bedded down with a metabolic rate 160% of that of the scientists. A nice roaring level of heat production that continued through the night. They maintained a high level of metabolism during the night with bouts of shivering that they slept through the night in naked comfort. Rectal temperatures were maintained at 97 F. Their skin temperatures fell to cool 82.4 F -- about 2 F cooler than the scientists. Their little feet remained warmer than the scientists. Unlike the Australians, the Indians of Tierra del Fuego have a metabolic solution to keeping warm. An ample source of calories is needed to fuel this solution.
Four centuries BC, Xenophon, soldier of fortune and historian led a retreating Spartan army across the Carduchian Mountains. The winds were piercing. The air WAS bitterly cold. “Toes dropped off from frostbite.” Xenophon successfully returned his troops home, sans some toes and noses. Frostbite is not lethal but rather a “strategy” to sacrifice peripheral tissues in favor of core body heat.
In 1683, Robert Boyle penned his famous advice on the avoidance of frostbite: “Rub them well with snow and escape unharmed.” Well, the Boyle era has ended. The mantra today is -- warm it and don’t rub it.