Lawrence Henderson, head of the Fatigue Lab, initially saw the role of his new laboratory as carrying forward the work of his previous lab at the Medical School: a study of acid-base balance in the body, gas exchange in the respiratory cycle, and the physiology of exercise.

Under the day-to-day supervision of School of Public Health Professor Bruce Dill, the Fatigue Lab’s small staff set out to establish the constants of human blood chemistry, and how those constants might relate to industrial settings.

Ultimately, this turned out to be a low-potential field for industrial research. Henderson, undaunted, expanded his lab’s focus. Between in 1929 and 1940, researchers on multiple field studies investigated the human body’s ability to adapt and acclimatize to extreme environmental conditions—dry and wet heat, dry and wet cold, and high altitudes.

The most successful of these field studies was conducted in the summers of 1932 and 1934. At the site of the half-finished Boulder Dam, the Fatigue Lab’s researchers concluded in 1932 that the problems of construction workers at the site—including cramps, heat prostration, and even death—were the result of salt loss through sweat. This finding was confirmed in the steel mills of Youngstown, Ohio, which in 1934 suffered through one of the hottest summers on record. The Fatigue Lab’s practical recommendation that workers increase their salt intake prompted an effusive letter of thanks from the Health Officer of the Youngstown Sheet and Tube Company.

“The prospect of death during hot weather, due to heat exhaustion and cramps, has been an ever-present nightmare for many years,” he wrote. “You have shown us how to handle them in such a way that the fears which have beset us in the past can be banished and put away forever.”

It was an unexpected and welcome triumph. Dean Donham relayed the new to the Rockefeller Foundation, the principal financial backer of the research, shortly afterwards. “There is certainly a thrill,” Donham wrote, “in scientific work which comes through as this appears to have done.”

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Fatigue Lab test subjects
Boulder Dam, site of Fatigue Lab research