Controlling dust from activities like this was on the minds of those in the Department of Labor in the 1930s, as silicosis, a lung disease, was taking a toll on American workers. Above, a worker jackhammers into rock in Lassen National Forest in California in 1934, preparing to shoot explosives. U.S. Forest Service/Oregon State University Libraries hide caption

itoggle caption U.S. Forest Service/Oregon State University Libraries

Chris Stephens, 28, who has been battling depression all of his life, plays with his dogs at home in Concord, Calif., on Friday. After a dose of ketamine, Stephens says, "I actually wanted to do things. I wanted to live life." Lianne Milton for NPR hide caption

itoggle caption Lianne Milton for NPR

Nonnative pythons, like this one, are invading the Florida Everglades. As a top predator, the snakes have crippled the populations of rabbits, raccoons and other animals. Joe Raedle/Getty Images hide caption

itoggle caption Joe Raedle/Getty Images

Ketamine has been used as an anesthetic for decades. It's also a widely popular but illegal club drug known as "Special K." When administered in low doses, patients report a rapid reduction in depression symptoms. Huw Golledge/flickr hide caption

itoggle caption Huw Golledge/flickr

The Delboeuf illusion makes one dot appear larger than the other. But they're the same size. Your brain is misled by comparing the dots to the surrounding circles. Washiucho/Wikimedia Commons hide caption

itoggle caption Washiucho/Wikimedia Commons