In 1917, American health officials in El Paso, Texas, launched a campaign to use toxic chemicals, including gasoline baths, to disinfect immigrants seeking to enter the United States through the US-Mexico border.

Only a few days after the alarming practice was launched at the border, one Mexican woman refused to go through it, sparking a protest of thousands of Mexicans at the El Paso border. Her name was Carmelita Torres; she was a 17-year-old maid from Juarez who crossed the border daily for work.

Although Torres and the riots briefly shut down the border, the campaign would continue for decades and even go on to inspire Nazi scientists. In this video, we trace the dangerous policies that lasted well into the 1960s, from the forced kerosene baths to the use of the poisonous gas Zyklon B to the fumigations of migrant workers in the “Bracero program” using the pesticide DDT. Watch the video above to learn more about this long history of toxic chemicals at the border.

Join our Reddit AMA! Today at 3 pm ET/12 pm PT, you can join me and historian David Dorado Romo on Reddit r/IAmA to discuss the latest episode. We’ll talk about the dark history of disinfection and discrimination at the border, how we researched this topic, and how the video came together. Ask us anything!

If you want to learn more about the “Bath Riots,” check out David Dorado Romo’s book Ringside Seat to a Revolution. And for more on the Bracero program, check out the Bracero History Archive.

This is the second installment in Missing Chapter, where we revisit underreported and often overlooked moments of the past to give context to the present. Our first season covers stories of racial injustice, political conflicts, even the hidden history of US medical experimentation. If you have an idea for a topic we should investigate in the series, send it to me via this form!

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